mv compiler to compiler/

39 files changed, 9614 insertions, 0 deletions

diff --git a/compiler/rustc_builtin_macros/src/asm.rs b/compiler/rustc_builtin_macros/src/asm.rs
new file mode 100644
index 00000000000..5dafd6b77ab
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/asm.rs
@@ -0,0 +1,632 @@
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::{Applicability, DiagnosticBuilder};
+use rustc_expand::base::{self, *};
+use rustc_parse::parser::Parser;
+use rustc_parse_format as parse;
+use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::{InnerSpan, Span};
+
+struct AsmArgs {
+    templates: Vec<P<ast::Expr>>,
+    operands: Vec<(ast::InlineAsmOperand, Span)>,
+    named_args: FxHashMap<Symbol, usize>,
+    reg_args: FxHashSet<usize>,
+    options: ast::InlineAsmOptions,
+    options_spans: Vec<Span>,
+}
+
+fn parse_args<'a>(
+    ecx: &mut ExtCtxt<'a>,
+    sp: Span,
+    tts: TokenStream,
+) -> Result<AsmArgs, DiagnosticBuilder<'a>> {
+    let mut p = ecx.new_parser_from_tts(tts);
+
+    if p.token == token::Eof {
+        return Err(ecx.struct_span_err(sp, "requires at least a template string argument"));
+    }
+
+    // Detect use of the legacy llvm_asm! syntax (which used to be called asm!)
+    if p.look_ahead(1, |t| *t == token::Colon || *t == token::ModSep) {
+        let mut err =
+            ecx.struct_span_err(sp, "the legacy LLVM-style asm! syntax is no longer supported");
+        err.note("consider migrating to the new asm! syntax specified in RFC 2873");
+        err.note("alternatively, switch to llvm_asm! to keep your code working as it is");
+
+        // Find the span of the "asm!" so that we can offer an automatic suggestion
+        let asm_span = sp.from_inner(InnerSpan::new(0, 4));
+        if let Ok(s) = ecx.source_map().span_to_snippet(asm_span) {
+            if s == "asm!" {
+                err.span_suggestion(
+                    asm_span,
+                    "replace with",
+                    "llvm_asm!".into(),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        return Err(err);
+    }
+
+    let first_template = p.parse_expr()?;
+    let mut args = AsmArgs {
+        templates: vec![first_template],
+        operands: vec![],
+        named_args: FxHashMap::default(),
+        reg_args: FxHashSet::default(),
+        options: ast::InlineAsmOptions::empty(),
+        options_spans: vec![],
+    };
+
+    let mut allow_templates = true;
+    while p.token != token::Eof {
+        if !p.eat(&token::Comma) {
+            if allow_templates {
+                // After a template string, we always expect *only* a comma...
+                let mut err = ecx.struct_span_err(p.token.span, "expected token: `,`");
+                err.span_label(p.token.span, "expected `,`");
+                p.maybe_annotate_with_ascription(&mut err, false);
+                return Err(err);
+            } else {
+                // ...after that delegate to `expect` to also include the other expected tokens.
+                return Err(p.expect(&token::Comma).err().unwrap());
+            }
+        }
+        if p.token == token::Eof {
+            break;
+        } // accept trailing commas
+
+        // Parse options
+        if p.eat(&token::Ident(sym::options, false)) {
+            parse_options(&mut p, &mut args)?;
+            allow_templates = false;
+            continue;
+        }
+
+        let span_start = p.token.span;
+
+        // Parse operand names
+        let name = if p.token.is_ident() && p.look_ahead(1, |t| *t == token::Eq) {
+            let (ident, _) = p.token.ident().unwrap();
+            p.bump();
+            p.expect(&token::Eq)?;
+            allow_templates = false;
+            Some(ident.name)
+        } else {
+            None
+        };
+
+        let mut explicit_reg = false;
+        let op = if p.eat(&token::Ident(kw::In, false)) {
+            let reg = parse_reg(&mut p, &mut explicit_reg)?;
+            let expr = p.parse_expr()?;
+            ast::InlineAsmOperand::In { reg, expr }
+        } else if p.eat(&token::Ident(sym::out, false)) {
+            let reg = parse_reg(&mut p, &mut explicit_reg)?;
+            let expr = if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
+            ast::InlineAsmOperand::Out { reg, expr, late: false }
+        } else if p.eat(&token::Ident(sym::lateout, false)) {
+            let reg = parse_reg(&mut p, &mut explicit_reg)?;
+            let expr = if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
+            ast::InlineAsmOperand::Out { reg, expr, late: true }
+        } else if p.eat(&token::Ident(sym::inout, false)) {
+            let reg = parse_reg(&mut p, &mut explicit_reg)?;
+            let expr = p.parse_expr()?;
+            if p.eat(&token::FatArrow) {
+                let out_expr =
+                    if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
+                ast::InlineAsmOperand::SplitInOut { reg, in_expr: expr, out_expr, late: false }
+            } else {
+                ast::InlineAsmOperand::InOut { reg, expr, late: false }
+            }
+        } else if p.eat(&token::Ident(sym::inlateout, false)) {
+            let reg = parse_reg(&mut p, &mut explicit_reg)?;
+            let expr = p.parse_expr()?;
+            if p.eat(&token::FatArrow) {
+                let out_expr =
+                    if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
+                ast::InlineAsmOperand::SplitInOut { reg, in_expr: expr, out_expr, late: true }
+            } else {
+                ast::InlineAsmOperand::InOut { reg, expr, late: true }
+            }
+        } else if p.eat(&token::Ident(kw::Const, false)) {
+            let expr = p.parse_expr()?;
+            ast::InlineAsmOperand::Const { expr }
+        } else if p.eat(&token::Ident(sym::sym, false)) {
+            let expr = p.parse_expr()?;
+            match expr.kind {
+                ast::ExprKind::Path(..) => {}
+                _ => {
+                    let err = ecx
+                        .struct_span_err(expr.span, "argument to `sym` must be a path expression");
+                    return Err(err);
+                }
+            }
+            ast::InlineAsmOperand::Sym { expr }
+        } else if allow_templates {
+            let template = p.parse_expr()?;
+            // If it can't possibly expand to a string, provide diagnostics here to include other
+            // things it could have been.
+            match template.kind {
+                ast::ExprKind::Lit(ast::Lit { kind: ast::LitKind::Str(..), .. }) => {}
+                ast::ExprKind::MacCall(..) => {}
+                _ => {
+                    let errstr = "expected operand, options, or additional template string";
+                    let mut err = ecx.struct_span_err(template.span, errstr);
+                    err.span_label(template.span, errstr);
+                    return Err(err);
+                }
+            }
+            args.templates.push(template);
+            continue;
+        } else {
+            return Err(p.expect_one_of(&[], &[]).unwrap_err());
+        };
+
+        allow_templates = false;
+        let span = span_start.to(p.prev_token.span);
+        let slot = args.operands.len();
+        args.operands.push((op, span));
+
+        // Validate the order of named, positional & explicit register operands and options. We do
+        // this at the end once we have the full span of the argument available.
+        if !args.options_spans.is_empty() {
+            ecx.struct_span_err(span, "arguments are not allowed after options")
+                .span_labels(args.options_spans.clone(), "previous options")
+                .span_label(span, "argument")
+                .emit();
+        }
+        if explicit_reg {
+            if name.is_some() {
+                ecx.struct_span_err(span, "explicit register arguments cannot have names").emit();
+            }
+            args.reg_args.insert(slot);
+        } else if let Some(name) = name {
+            if let Some(&prev) = args.named_args.get(&name) {
+                ecx.struct_span_err(span, &format!("duplicate argument named `{}`", name))
+                    .span_label(args.operands[prev].1, "previously here")
+                    .span_label(span, "duplicate argument")
+                    .emit();
+                continue;
+            }
+            if !args.reg_args.is_empty() {
+                let mut err = ecx.struct_span_err(
+                    span,
+                    "named arguments cannot follow explicit register arguments",
+                );
+                err.span_label(span, "named argument");
+                for pos in &args.reg_args {
+                    err.span_label(args.operands[*pos].1, "explicit register argument");
+                }
+                err.emit();
+            }
+            args.named_args.insert(name, slot);
+        } else {
+            if !args.named_args.is_empty() || !args.reg_args.is_empty() {
+                let mut err = ecx.struct_span_err(
+                    span,
+                    "positional arguments cannot follow named arguments \
+                     or explicit register arguments",
+                );
+                err.span_label(span, "positional argument");
+                for pos in args.named_args.values() {
+                    err.span_label(args.operands[*pos].1, "named argument");
+                }
+                for pos in &args.reg_args {
+                    err.span_label(args.operands[*pos].1, "explicit register argument");
+                }
+                err.emit();
+            }
+        }
+    }
+
+    if args.options.contains(ast::InlineAsmOptions::NOMEM)
+        && args.options.contains(ast::InlineAsmOptions::READONLY)
+    {
+        let spans = args.options_spans.clone();
+        ecx.struct_span_err(spans, "the `nomem` and `readonly` options are mutually exclusive")
+            .emit();
+    }
+    if args.options.contains(ast::InlineAsmOptions::PURE)
+        && args.options.contains(ast::InlineAsmOptions::NORETURN)
+    {
+        let spans = args.options_spans.clone();
+        ecx.struct_span_err(spans, "the `pure` and `noreturn` options are mutually exclusive")
+            .emit();
+    }
+    if args.options.contains(ast::InlineAsmOptions::PURE)
+        && !args.options.intersects(ast::InlineAsmOptions::NOMEM | ast::InlineAsmOptions::READONLY)
+    {
+        let spans = args.options_spans.clone();
+        ecx.struct_span_err(
+            spans,
+            "the `pure` option must be combined with either `nomem` or `readonly`",
+        )
+        .emit();
+    }
+
+    let mut have_real_output = false;
+    let mut outputs_sp = vec![];
+    for (op, op_sp) in &args.operands {
+        match op {
+            ast::InlineAsmOperand::Out { expr, .. }
+            | ast::InlineAsmOperand::SplitInOut { out_expr: expr, .. } => {
+                outputs_sp.push(*op_sp);
+                have_real_output |= expr.is_some();
+            }
+            ast::InlineAsmOperand::InOut { .. } => {
+                outputs_sp.push(*op_sp);
+                have_real_output = true;
+            }
+            _ => {}
+        }
+    }
+    if args.options.contains(ast::InlineAsmOptions::PURE) && !have_real_output {
+        ecx.struct_span_err(
+            args.options_spans.clone(),
+            "asm with `pure` option must have at least one output",
+        )
+        .emit();
+    }
+    if args.options.contains(ast::InlineAsmOptions::NORETURN) && !outputs_sp.is_empty() {
+        let err = ecx
+            .struct_span_err(outputs_sp, "asm outputs are not allowed with the `noreturn` option");
+
+        // Bail out now since this is likely to confuse MIR
+        return Err(err);
+    }
+
+    Ok(args)
+}
+
+/// Report a duplicate option error.
+///
+/// This function must be called immediately after the option token is parsed.
+/// Otherwise, the suggestion will be incorrect.
+fn err_duplicate_option<'a>(p: &mut Parser<'a>, symbol: Symbol, span: Span) {
+    let mut err = p
+        .sess
+        .span_diagnostic
+        .struct_span_err(span, &format!("the `{}` option was already provided", symbol));
+    err.span_label(span, "this option was already provided");
+
+    // Tool-only output
+    let mut full_span = span;
+    if p.token.kind == token::Comma {
+        full_span = full_span.to(p.token.span);
+    }
+    err.tool_only_span_suggestion(
+        full_span,
+        "remove this option",
+        String::new(),
+        Applicability::MachineApplicable,
+    );
+
+    err.emit();
+}
+
+/// Try to set the provided option in the provided `AsmArgs`.
+/// If it is already set, report a duplicate option error.
+///
+/// This function must be called immediately after the option token is parsed.
+/// Otherwise, the error will not point to the correct spot.
+fn try_set_option<'a>(
+    p: &mut Parser<'a>,
+    args: &mut AsmArgs,
+    symbol: Symbol,
+    option: ast::InlineAsmOptions,
+) {
+    if !args.options.contains(option) {
+        args.options |= option;
+    } else {
+        err_duplicate_option(p, symbol, p.prev_token.span);
+    }
+}
+
+fn parse_options<'a>(p: &mut Parser<'a>, args: &mut AsmArgs) -> Result<(), DiagnosticBuilder<'a>> {
+    let span_start = p.prev_token.span;
+
+    p.expect(&token::OpenDelim(token::DelimToken::Paren))?;
+
+    while !p.eat(&token::CloseDelim(token::DelimToken::Paren)) {
+        if p.eat(&token::Ident(sym::pure, false)) {
+            try_set_option(p, args, sym::pure, ast::InlineAsmOptions::PURE);
+        } else if p.eat(&token::Ident(sym::nomem, false)) {
+            try_set_option(p, args, sym::nomem, ast::InlineAsmOptions::NOMEM);
+        } else if p.eat(&token::Ident(sym::readonly, false)) {
+            try_set_option(p, args, sym::readonly, ast::InlineAsmOptions::READONLY);
+        } else if p.eat(&token::Ident(sym::preserves_flags, false)) {
+            try_set_option(p, args, sym::preserves_flags, ast::InlineAsmOptions::PRESERVES_FLAGS);
+        } else if p.eat(&token::Ident(sym::noreturn, false)) {
+            try_set_option(p, args, sym::noreturn, ast::InlineAsmOptions::NORETURN);
+        } else if p.eat(&token::Ident(sym::nostack, false)) {
+            try_set_option(p, args, sym::nostack, ast::InlineAsmOptions::NOSTACK);
+        } else {
+            p.expect(&token::Ident(sym::att_syntax, false))?;
+            try_set_option(p, args, sym::att_syntax, ast::InlineAsmOptions::ATT_SYNTAX);
+        }
+
+        // Allow trailing commas
+        if p.eat(&token::CloseDelim(token::DelimToken::Paren)) {
+            break;
+        }
+        p.expect(&token::Comma)?;
+    }
+
+    let new_span = span_start.to(p.prev_token.span);
+    args.options_spans.push(new_span);
+
+    Ok(())
+}
+
+fn parse_reg<'a>(
+    p: &mut Parser<'a>,
+    explicit_reg: &mut bool,
+) -> Result<ast::InlineAsmRegOrRegClass, DiagnosticBuilder<'a>> {
+    p.expect(&token::OpenDelim(token::DelimToken::Paren))?;
+    let result = match p.token.kind {
+        token::Ident(name, false) => ast::InlineAsmRegOrRegClass::RegClass(name),
+        token::Literal(token::Lit { kind: token::LitKind::Str, symbol, suffix: _ }) => {
+            *explicit_reg = true;
+            ast::InlineAsmRegOrRegClass::Reg(symbol)
+        }
+        _ => {
+            return Err(
+                p.struct_span_err(p.token.span, "expected register class or explicit register")
+            );
+        }
+    };
+    p.bump();
+    p.expect(&token::CloseDelim(token::DelimToken::Paren))?;
+    Ok(result)
+}
+
+fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, sp: Span, args: AsmArgs) -> P<ast::Expr> {
+    let mut template = vec![];
+    // Register operands are implicitly used since they are not allowed to be
+    // referenced in the template string.
+    let mut used = vec![false; args.operands.len()];
+    for pos in &args.reg_args {
+        used[*pos] = true;
+    }
+    let named_pos: FxHashMap<usize, Symbol> =
+        args.named_args.iter().map(|(&sym, &idx)| (idx, sym)).collect();
+    let mut line_spans = Vec::with_capacity(args.templates.len());
+    let mut curarg = 0;
+
+    for template_expr in args.templates.into_iter() {
+        if !template.is_empty() {
+            template.push(ast::InlineAsmTemplatePiece::String("\n".to_string()));
+        }
+
+        let msg = "asm template must be a string literal";
+        let template_sp = template_expr.span;
+        let (template_str, template_style, template_span) =
+            match expr_to_spanned_string(ecx, template_expr, msg) {
+                Ok(template_part) => template_part,
+                Err(err) => {
+                    if let Some(mut err) = err {
+                        err.emit();
+                    }
+                    return DummyResult::raw_expr(sp, true);
+                }
+            };
+
+        let str_style = match template_style {
+            ast::StrStyle::Cooked => None,
+            ast::StrStyle::Raw(raw) => Some(raw as usize),
+        };
+
+        let template_str = &template_str.as_str();
+        let template_snippet = ecx.source_map().span_to_snippet(template_sp).ok();
+        let mut parser = parse::Parser::new(
+            template_str,
+            str_style,
+            template_snippet,
+            false,
+            parse::ParseMode::InlineAsm,
+        );
+        parser.curarg = curarg;
+
+        let mut unverified_pieces = Vec::new();
+        while let Some(piece) = parser.next() {
+            if !parser.errors.is_empty() {
+                break;
+            } else {
+                unverified_pieces.push(piece);
+            }
+        }
+
+        if !parser.errors.is_empty() {
+            let err = parser.errors.remove(0);
+            let err_sp = template_span.from_inner(err.span);
+            let msg = &format!("invalid asm template string: {}", err.description);
+            let mut e = ecx.struct_span_err(err_sp, msg);
+            e.span_label(err_sp, err.label + " in asm template string");
+            if let Some(note) = err.note {
+                e.note(&note);
+            }
+            if let Some((label, span)) = err.secondary_label {
+                let err_sp = template_span.from_inner(span);
+                e.span_label(err_sp, label);
+            }
+            e.emit();
+            return DummyResult::raw_expr(sp, true);
+        }
+
+        curarg = parser.curarg;
+
+        let mut arg_spans = parser.arg_places.iter().map(|span| template_span.from_inner(*span));
+        for piece in unverified_pieces {
+            match piece {
+                parse::Piece::String(s) => {
+                    template.push(ast::InlineAsmTemplatePiece::String(s.to_string()))
+                }
+                parse::Piece::NextArgument(arg) => {
+                    let span = arg_spans.next().unwrap_or(template_sp);
+
+                    let operand_idx = match arg.position {
+                        parse::ArgumentIs(idx) | parse::ArgumentImplicitlyIs(idx) => {
+                            if idx >= args.operands.len()
+                                || named_pos.contains_key(&idx)
+                                || args.reg_args.contains(&idx)
+                            {
+                                let msg = format!("invalid reference to argument at index {}", idx);
+                                let mut err = ecx.struct_span_err(span, &msg);
+                                err.span_label(span, "from here");
+
+                                let positional_args = args.operands.len()
+                                    - args.named_args.len()
+                                    - args.reg_args.len();
+                                let positional = if positional_args != args.operands.len() {
+                                    "positional "
+                                } else {
+                                    ""
+                                };
+                                let msg = match positional_args {
+                                    0 => format!("no {}arguments were given", positional),
+                                    1 => format!("there is 1 {}argument", positional),
+                                    x => format!("there are {} {}arguments", x, positional),
+                                };
+                                err.note(&msg);
+
+                                if named_pos.contains_key(&idx) {
+                                    err.span_label(args.operands[idx].1, "named argument");
+                                    err.span_note(
+                                        args.operands[idx].1,
+                                        "named arguments cannot be referenced by position",
+                                    );
+                                } else if args.reg_args.contains(&idx) {
+                                    err.span_label(
+                                        args.operands[idx].1,
+                                        "explicit register argument",
+                                    );
+                                    err.span_note(
+                                        args.operands[idx].1,
+                                        "explicit register arguments cannot be used in the asm template",
+                                    );
+                                }
+                                err.emit();
+                                None
+                            } else {
+                                Some(idx)
+                            }
+                        }
+                        parse::ArgumentNamed(name) => match args.named_args.get(&name) {
+                            Some(&idx) => Some(idx),
+                            None => {
+                                let msg = format!("there is no argument named `{}`", name);
+                                ecx.struct_span_err(span, &msg[..]).emit();
+                                None
+                            }
+                        },
+                    };
+
+                    let mut chars = arg.format.ty.chars();
+                    let mut modifier = chars.next();
+                    if chars.next().is_some() {
+                        let span = arg
+                            .format
+                            .ty_span
+                            .map(|sp| template_sp.from_inner(sp))
+                            .unwrap_or(template_sp);
+                        ecx.struct_span_err(
+                            span,
+                            "asm template modifier must be a single character",
+                        )
+                        .emit();
+                        modifier = None;
+                    }
+
+                    if let Some(operand_idx) = operand_idx {
+                        used[operand_idx] = true;
+                        template.push(ast::InlineAsmTemplatePiece::Placeholder {
+                            operand_idx,
+                            modifier,
+                            span,
+                        });
+                    }
+                }
+            }
+        }
+
+        if parser.line_spans.is_empty() {
+            let template_num_lines = 1 + template_str.matches('\n').count();
+            line_spans.extend(std::iter::repeat(template_sp).take(template_num_lines));
+        } else {
+            line_spans.extend(parser.line_spans.iter().map(|span| template_span.from_inner(*span)));
+        };
+    }
+
+    let mut unused_operands = vec![];
+    let mut help_str = String::new();
+    for (idx, used) in used.into_iter().enumerate() {
+        if !used {
+            let msg = if let Some(sym) = named_pos.get(&idx) {
+                help_str.push_str(&format!(" {{{}}}", sym));
+                "named argument never used"
+            } else {
+                help_str.push_str(&format!(" {{{}}}", idx));
+                "argument never used"
+            };
+            unused_operands.push((args.operands[idx].1, msg));
+        }
+    }
+    match unused_operands.len() {
+        0 => {}
+        1 => {
+            let (sp, msg) = unused_operands.into_iter().next().unwrap();
+            let mut err = ecx.struct_span_err(sp, msg);
+            err.span_label(sp, msg);
+            err.help(&format!(
+                "if this argument is intentionally unused, \
+                 consider using it in an asm comment: `\"/*{} */\"`",
+                help_str
+            ));
+            err.emit();
+        }
+        _ => {
+            let mut err = ecx.struct_span_err(
+                unused_operands.iter().map(|&(sp, _)| sp).collect::<Vec<Span>>(),
+                "multiple unused asm arguments",
+            );
+            for (sp, msg) in unused_operands {
+                err.span_label(sp, msg);
+            }
+            err.help(&format!(
+                "if these arguments are intentionally unused, \
+                 consider using them in an asm comment: `\"/*{} */\"`",
+                help_str
+            ));
+            err.emit();
+        }
+    }
+
+    let inline_asm =
+        ast::InlineAsm { template, operands: args.operands, options: args.options, line_spans };
+    P(ast::Expr {
+        id: ast::DUMMY_NODE_ID,
+        kind: ast::ExprKind::InlineAsm(P(inline_asm)),
+        span: sp,
+        attrs: ast::AttrVec::new(),
+        tokens: None,
+    })
+}
+
+pub fn expand_asm<'cx>(
+    ecx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    match parse_args(ecx, sp, tts) {
+        Ok(args) => MacEager::expr(expand_preparsed_asm(ecx, sp, args)),
+        Err(mut err) => {
+            err.emit();
+            DummyResult::any(sp)
+        }
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/assert.rs b/compiler/rustc_builtin_macros/src/assert.rs
new file mode 100644
index 00000000000..25181715540
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/assert.rs
@@ -0,0 +1,133 @@
+use rustc_errors::{Applicability, DiagnosticBuilder};
+
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, TokenKind};
+use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
+use rustc_ast::{self as ast, *};
+use rustc_ast_pretty::pprust;
+use rustc_expand::base::*;
+use rustc_parse::parser::Parser;
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+
+pub fn expand_assert<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn MacResult + 'cx> {
+    let Assert { cond_expr, custom_message } = match parse_assert(cx, sp, tts) {
+        Ok(assert) => assert,
+        Err(mut err) => {
+            err.emit();
+            return DummyResult::any(sp);
+        }
+    };
+
+    // `core::panic` and `std::panic` are different macros, so we use call-site
+    // context to pick up whichever is currently in scope.
+    let sp = cx.with_call_site_ctxt(sp);
+    let tokens = custom_message.unwrap_or_else(|| {
+        TokenStream::from(TokenTree::token(
+            TokenKind::lit(
+                token::Str,
+                Symbol::intern(&format!(
+                    "assertion failed: {}",
+                    pprust::expr_to_string(&cond_expr).escape_debug()
+                )),
+                None,
+            ),
+            DUMMY_SP,
+        ))
+    });
+    let args = P(MacArgs::Delimited(DelimSpan::from_single(sp), MacDelimiter::Parenthesis, tokens));
+    let panic_call = MacCall {
+        path: Path::from_ident(Ident::new(sym::panic, sp)),
+        args,
+        prior_type_ascription: None,
+    };
+    let if_expr = cx.expr_if(
+        sp,
+        cx.expr(sp, ExprKind::Unary(UnOp::Not, cond_expr)),
+        cx.expr(sp, ExprKind::MacCall(panic_call)),
+        None,
+    );
+    MacEager::expr(if_expr)
+}
+
+struct Assert {
+    cond_expr: P<ast::Expr>,
+    custom_message: Option<TokenStream>,
+}
+
+fn parse_assert<'a>(
+    cx: &mut ExtCtxt<'a>,
+    sp: Span,
+    stream: TokenStream,
+) -> Result<Assert, DiagnosticBuilder<'a>> {
+    let mut parser = cx.new_parser_from_tts(stream);
+
+    if parser.token == token::Eof {
+        let mut err = cx.struct_span_err(sp, "macro requires a boolean expression as an argument");
+        err.span_label(sp, "boolean expression required");
+        return Err(err);
+    }
+
+    let cond_expr = parser.parse_expr()?;
+
+    // Some crates use the `assert!` macro in the following form (note extra semicolon):
+    //
+    // assert!(
+    //     my_function();
+    // );
+    //
+    // Emit an error about semicolon and suggest removing it.
+    if parser.token == token::Semi {
+        let mut err = cx.struct_span_err(sp, "macro requires an expression as an argument");
+        err.span_suggestion(
+            parser.token.span,
+            "try removing semicolon",
+            String::new(),
+            Applicability::MaybeIncorrect,
+        );
+        err.emit();
+
+        parser.bump();
+    }
+
+    // Some crates use the `assert!` macro in the following form (note missing comma before
+    // message):
+    //
+    // assert!(true "error message");
+    //
+    // Emit an error and suggest inserting a comma.
+    let custom_message =
+        if let token::Literal(token::Lit { kind: token::Str, .. }) = parser.token.kind {
+            let mut err = cx.struct_span_err(parser.token.span, "unexpected string literal");
+            let comma_span = parser.prev_token.span.shrink_to_hi();
+            err.span_suggestion_short(
+                comma_span,
+                "try adding a comma",
+                ", ".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+            err.emit();
+
+            parse_custom_message(&mut parser)
+        } else if parser.eat(&token::Comma) {
+            parse_custom_message(&mut parser)
+        } else {
+            None
+        };
+
+    if parser.token != token::Eof {
+        parser.expect_one_of(&[], &[])?;
+        unreachable!();
+    }
+
+    Ok(Assert { cond_expr, custom_message })
+}
+
+fn parse_custom_message(parser: &mut Parser<'_>) -> Option<TokenStream> {
+    let ts = parser.parse_tokens();
+    if !ts.is_empty() { Some(ts) } else { None }
+}
diff --git a/compiler/rustc_builtin_macros/src/cfg.rs b/compiler/rustc_builtin_macros/src/cfg.rs
new file mode 100644
index 00000000000..4c00162b556
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/cfg.rs
@@ -0,0 +1,54 @@
+//! The compiler code necessary to support the cfg! extension, which expands to
+//! a literal `true` or `false` based on whether the given cfg matches the
+//! current compilation environment.
+
+use rustc_ast as ast;
+use rustc_ast::token;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_attr as attr;
+use rustc_errors::DiagnosticBuilder;
+use rustc_expand::base::{self, *};
+use rustc_span::Span;
+
+pub fn expand_cfg(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+
+    match parse_cfg(cx, sp, tts) {
+        Ok(cfg) => {
+            let matches_cfg = attr::cfg_matches(&cfg, &cx.sess.parse_sess, cx.ecfg.features);
+            MacEager::expr(cx.expr_bool(sp, matches_cfg))
+        }
+        Err(mut err) => {
+            err.emit();
+            DummyResult::any(sp)
+        }
+    }
+}
+
+fn parse_cfg<'a>(
+    cx: &mut ExtCtxt<'a>,
+    sp: Span,
+    tts: TokenStream,
+) -> Result<ast::MetaItem, DiagnosticBuilder<'a>> {
+    let mut p = cx.new_parser_from_tts(tts);
+
+    if p.token == token::Eof {
+        let mut err = cx.struct_span_err(sp, "macro requires a cfg-pattern as an argument");
+        err.span_label(sp, "cfg-pattern required");
+        return Err(err);
+    }
+
+    let cfg = p.parse_meta_item()?;
+
+    let _ = p.eat(&token::Comma);
+
+    if !p.eat(&token::Eof) {
+        return Err(cx.struct_span_err(sp, "expected 1 cfg-pattern"));
+    }
+
+    Ok(cfg)
+}
diff --git a/compiler/rustc_builtin_macros/src/cfg_accessible.rs b/compiler/rustc_builtin_macros/src/cfg_accessible.rs
new file mode 100644
index 00000000000..75f4b077640
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/cfg_accessible.rs
@@ -0,0 +1,59 @@
+//! Implementation of the `#[cfg_accessible(path)]` attribute macro.
+
+use rustc_ast as ast;
+use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
+use rustc_feature::AttributeTemplate;
+use rustc_parse::validate_attr;
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+
+crate struct Expander;
+
+fn validate_input<'a>(ecx: &mut ExtCtxt<'_>, mi: &'a ast::MetaItem) -> Option<&'a ast::Path> {
+    match mi.meta_item_list() {
+        None => {}
+        Some([]) => ecx.span_err(mi.span, "`cfg_accessible` path is not specified"),
+        Some([_, .., l]) => ecx.span_err(l.span(), "multiple `cfg_accessible` paths are specified"),
+        Some([nmi]) => match nmi.meta_item() {
+            None => ecx.span_err(nmi.span(), "`cfg_accessible` path cannot be a literal"),
+            Some(mi) => {
+                if !mi.is_word() {
+                    ecx.span_err(mi.span, "`cfg_accessible` path cannot accept arguments");
+                }
+                return Some(&mi.path);
+            }
+        },
+    }
+    None
+}
+
+impl MultiItemModifier for Expander {
+    fn expand(
+        &self,
+        ecx: &mut ExtCtxt<'_>,
+        _span: Span,
+        meta_item: &ast::MetaItem,
+        item: Annotatable,
+    ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
+        let template = AttributeTemplate { list: Some("path"), ..Default::default() };
+        let attr = &ecx.attribute(meta_item.clone());
+        validate_attr::check_builtin_attribute(
+            &ecx.sess.parse_sess,
+            attr,
+            sym::cfg_accessible,
+            template,
+        );
+
+        let path = match validate_input(ecx, meta_item) {
+            Some(path) => path,
+            None => return ExpandResult::Ready(Vec::new()),
+        };
+
+        let failure_msg = "cannot determine whether the path is accessible or not";
+        match ecx.resolver.cfg_accessible(ecx.current_expansion.id, path) {
+            Ok(true) => ExpandResult::Ready(vec![item]),
+            Ok(false) => ExpandResult::Ready(Vec::new()),
+            Err(_) => ExpandResult::Retry(item, failure_msg.into()),
+        }
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/cmdline_attrs.rs b/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
new file mode 100644
index 00000000000..34e2accc615
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
@@ -0,0 +1,35 @@
+//! Attributes injected into the crate root from command line using `-Z crate-attr`.
+
+use rustc_ast::attr::mk_attr;
+use rustc_ast::token;
+use rustc_ast::{self as ast, AttrItem, AttrStyle};
+use rustc_session::parse::ParseSess;
+use rustc_span::FileName;
+
+pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -> ast::Crate {
+    for raw_attr in attrs {
+        let mut parser = rustc_parse::new_parser_from_source_str(
+            parse_sess,
+            FileName::cli_crate_attr_source_code(&raw_attr),
+            raw_attr.clone(),
+        );
+
+        let start_span = parser.token.span;
+        let AttrItem { path, args } = match parser.parse_attr_item() {
+            Ok(ai) => ai,
+            Err(mut err) => {
+                err.emit();
+                continue;
+            }
+        };
+        let end_span = parser.token.span;
+        if parser.token != token::Eof {
+            parse_sess.span_diagnostic.span_err(start_span.to(end_span), "invalid crate attribute");
+            continue;
+        }
+
+        krate.attrs.push(mk_attr(AttrStyle::Inner, path, args, start_span.to(end_span)));
+    }
+
+    krate
+}
diff --git a/compiler/rustc_builtin_macros/src/compile_error.rs b/compiler/rustc_builtin_macros/src/compile_error.rs
new file mode 100644
index 00000000000..f5955604e5f
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/compile_error.rs
@@ -0,0 +1,20 @@
+// The compiler code necessary to support the compile_error! extension.
+
+use rustc_ast::tokenstream::TokenStream;
+use rustc_expand::base::{self, *};
+use rustc_span::Span;
+
+pub fn expand_compile_error<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    let var = match get_single_str_from_tts(cx, sp, tts, "compile_error!") {
+        None => return DummyResult::any(sp),
+        Some(v) => v,
+    };
+
+    cx.span_err(sp, &var);
+
+    DummyResult::any(sp)
+}
diff --git a/compiler/rustc_builtin_macros/src/concat.rs b/compiler/rustc_builtin_macros/src/concat.rs
new file mode 100644
index 00000000000..e5077d93674
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/concat.rs
@@ -0,0 +1,65 @@
+use rustc_ast as ast;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_expand::base::{self, DummyResult};
+use rustc_span::symbol::Symbol;
+
+use std::string::String;
+
+pub fn expand_concat(
+    cx: &mut base::ExtCtxt<'_>,
+    sp: rustc_span::Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let es = match base::get_exprs_from_tts(cx, sp, tts) {
+        Some(e) => e,
+        None => return DummyResult::any(sp),
+    };
+    let mut accumulator = String::new();
+    let mut missing_literal = vec![];
+    let mut has_errors = false;
+    for e in es {
+        match e.kind {
+            ast::ExprKind::Lit(ref lit) => match lit.kind {
+                ast::LitKind::Str(ref s, _) | ast::LitKind::Float(ref s, _) => {
+                    accumulator.push_str(&s.as_str());
+                }
+                ast::LitKind::Char(c) => {
+                    accumulator.push(c);
+                }
+                ast::LitKind::Int(
+                    i,
+                    ast::LitIntType::Unsigned(_)
+                    | ast::LitIntType::Signed(_)
+                    | ast::LitIntType::Unsuffixed,
+                ) => {
+                    accumulator.push_str(&i.to_string());
+                }
+                ast::LitKind::Bool(b) => {
+                    accumulator.push_str(&b.to_string());
+                }
+                ast::LitKind::Byte(..) | ast::LitKind::ByteStr(..) => {
+                    cx.span_err(e.span, "cannot concatenate a byte string literal");
+                }
+                ast::LitKind::Err(_) => {
+                    has_errors = true;
+                }
+            },
+            ast::ExprKind::Err => {
+                has_errors = true;
+            }
+            _ => {
+                missing_literal.push(e.span);
+            }
+        }
+    }
+    if !missing_literal.is_empty() {
+        let mut err = cx.struct_span_err(missing_literal, "expected a literal");
+        err.note("only literals (like `\"foo\"`, `42` and `3.14`) can be passed to `concat!()`");
+        err.emit();
+        return DummyResult::any(sp);
+    } else if has_errors {
+        return DummyResult::any(sp);
+    }
+    let sp = cx.with_def_site_ctxt(sp);
+    base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&accumulator)))
+}
diff --git a/compiler/rustc_builtin_macros/src/concat_idents.rs b/compiler/rustc_builtin_macros/src/concat_idents.rs
new file mode 100644
index 00000000000..8223cdda072
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/concat_idents.rs
@@ -0,0 +1,69 @@
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Token};
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_expand::base::{self, *};
+use rustc_span::symbol::{Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand_concat_idents<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    if tts.is_empty() {
+        cx.span_err(sp, "concat_idents! takes 1 or more arguments.");
+        return DummyResult::any(sp);
+    }
+
+    let mut res_str = String::new();
+    for (i, e) in tts.into_trees().enumerate() {
+        if i & 1 == 1 {
+            match e {
+                TokenTree::Token(Token { kind: token::Comma, .. }) => {}
+                _ => {
+                    cx.span_err(sp, "concat_idents! expecting comma.");
+                    return DummyResult::any(sp);
+                }
+            }
+        } else {
+            match e {
+                TokenTree::Token(Token { kind: token::Ident(name, _), .. }) => {
+                    res_str.push_str(&name.as_str())
+                }
+                _ => {
+                    cx.span_err(sp, "concat_idents! requires ident args.");
+                    return DummyResult::any(sp);
+                }
+            }
+        }
+    }
+
+    let ident = Ident::new(Symbol::intern(&res_str), cx.with_call_site_ctxt(sp));
+
+    struct ConcatIdentsResult {
+        ident: Ident,
+    }
+
+    impl base::MacResult for ConcatIdentsResult {
+        fn make_expr(self: Box<Self>) -> Option<P<ast::Expr>> {
+            Some(P(ast::Expr {
+                id: ast::DUMMY_NODE_ID,
+                kind: ast::ExprKind::Path(None, ast::Path::from_ident(self.ident)),
+                span: self.ident.span,
+                attrs: ast::AttrVec::new(),
+                tokens: None,
+            }))
+        }
+
+        fn make_ty(self: Box<Self>) -> Option<P<ast::Ty>> {
+            Some(P(ast::Ty {
+                id: ast::DUMMY_NODE_ID,
+                kind: ast::TyKind::Path(None, ast::Path::from_ident(self.ident)),
+                span: self.ident.span,
+            }))
+        }
+    }
+
+    Box::new(ConcatIdentsResult { ident })
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/bounds.rs b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
new file mode 100644
index 00000000000..12ef166b8b0
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
@@ -0,0 +1,29 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::path_std;
+
+use rustc_ast::MetaItem;
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::Span;
+
+pub fn expand_deriving_copy(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: path_std!(marker::Copy),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: true,
+        methods: Vec::new(),
+        associated_types: Vec::new(),
+    };
+
+    trait_def.expand(cx, mitem, item, push);
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
new file mode 100644
index 00000000000..957c8035399
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -0,0 +1,224 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::path_std;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, GenericArg, Generics, ItemKind, MetaItem, VariantData};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand_deriving_clone(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    // check if we can use a short form
+    //
+    // the short form is `fn clone(&self) -> Self { *self }`
+    //
+    // we can use the short form if:
+    // - the item is Copy (unfortunately, all we can check is whether it's also deriving Copy)
+    // - there are no generic parameters (after specialization this limitation can be removed)
+    //      if we used the short form with generics, we'd have to bound the generics with
+    //      Clone + Copy, and then there'd be no Clone impl at all if the user fills in something
+    //      that is Clone but not Copy. and until specialization we can't write both impls.
+    // - the item is a union with Copy fields
+    //      Unions with generic parameters still can derive Clone because they require Copy
+    //      for deriving, Clone alone is not enough.
+    //      Whever Clone is implemented for fields is irrelevant so we don't assert it.
+    let bounds;
+    let substructure;
+    let is_shallow;
+    match *item {
+        Annotatable::Item(ref annitem) => match annitem.kind {
+            ItemKind::Struct(_, Generics { ref params, .. })
+            | ItemKind::Enum(_, Generics { ref params, .. }) => {
+                let container_id = cx.current_expansion.id.expn_data().parent;
+                if cx.resolver.has_derive_copy(container_id)
+                    && !params.iter().any(|param| match param.kind {
+                        ast::GenericParamKind::Type { .. } => true,
+                        _ => false,
+                    })
+                {
+                    bounds = vec![];
+                    is_shallow = true;
+                    substructure = combine_substructure(Box::new(|c, s, sub| {
+                        cs_clone_shallow("Clone", c, s, sub, false)
+                    }));
+                } else {
+                    bounds = vec![];
+                    is_shallow = false;
+                    substructure =
+                        combine_substructure(Box::new(|c, s, sub| cs_clone("Clone", c, s, sub)));
+                }
+            }
+            ItemKind::Union(..) => {
+                bounds = vec![Literal(path_std!(marker::Copy))];
+                is_shallow = true;
+                substructure = combine_substructure(Box::new(|c, s, sub| {
+                    cs_clone_shallow("Clone", c, s, sub, true)
+                }));
+            }
+            _ => {
+                bounds = vec![];
+                is_shallow = false;
+                substructure =
+                    combine_substructure(Box::new(|c, s, sub| cs_clone("Clone", c, s, sub)));
+            }
+        },
+
+        _ => cx.span_bug(span, "`#[derive(Clone)]` on trait item or impl item"),
+    }
+
+    let inline = cx.meta_word(span, sym::inline);
+    let attrs = vec![cx.attribute(inline)];
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: path_std!(clone::Clone),
+        additional_bounds: bounds,
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: true,
+        methods: vec![MethodDef {
+            name: sym::clone,
+            generics: Bounds::empty(),
+            explicit_self: borrowed_explicit_self(),
+            args: Vec::new(),
+            ret_ty: Self_,
+            attributes: attrs,
+            is_unsafe: false,
+            unify_fieldless_variants: false,
+            combine_substructure: substructure,
+        }],
+        associated_types: Vec::new(),
+    };
+
+    trait_def.expand_ext(cx, mitem, item, push, is_shallow)
+}
+
+fn cs_clone_shallow(
+    name: &str,
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+    is_union: bool,
+) -> P<Expr> {
+    fn assert_ty_bounds(
+        cx: &mut ExtCtxt<'_>,
+        stmts: &mut Vec<ast::Stmt>,
+        ty: P<ast::Ty>,
+        span: Span,
+        helper_name: &str,
+    ) {
+        // Generate statement `let _: helper_name<ty>;`,
+        // set the expn ID so we can use the unstable struct.
+        let span = cx.with_def_site_ctxt(span);
+        let assert_path = cx.path_all(
+            span,
+            true,
+            cx.std_path(&[sym::clone, Symbol::intern(helper_name)]),
+            vec![GenericArg::Type(ty)],
+        );
+        stmts.push(cx.stmt_let_type_only(span, cx.ty_path(assert_path)));
+    }
+    fn process_variant(cx: &mut ExtCtxt<'_>, stmts: &mut Vec<ast::Stmt>, variant: &VariantData) {
+        for field in variant.fields() {
+            // let _: AssertParamIsClone<FieldTy>;
+            assert_ty_bounds(cx, stmts, field.ty.clone(), field.span, "AssertParamIsClone");
+        }
+    }
+
+    let mut stmts = Vec::new();
+    if is_union {
+        // let _: AssertParamIsCopy<Self>;
+        let self_ty = cx.ty_path(cx.path_ident(trait_span, Ident::with_dummy_span(kw::SelfUpper)));
+        assert_ty_bounds(cx, &mut stmts, self_ty, trait_span, "AssertParamIsCopy");
+    } else {
+        match *substr.fields {
+            StaticStruct(vdata, ..) => {
+                process_variant(cx, &mut stmts, vdata);
+            }
+            StaticEnum(enum_def, ..) => {
+                for variant in &enum_def.variants {
+                    process_variant(cx, &mut stmts, &variant.data);
+                }
+            }
+            _ => cx.span_bug(
+                trait_span,
+                &format!(
+                    "unexpected substructure in \
+                                                    shallow `derive({})`",
+                    name
+                ),
+            ),
+        }
+    }
+    stmts.push(cx.stmt_expr(cx.expr_deref(trait_span, cx.expr_self(trait_span))));
+    cx.expr_block(cx.block(trait_span, stmts))
+}
+
+fn cs_clone(
+    name: &str,
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+) -> P<Expr> {
+    let ctor_path;
+    let all_fields;
+    let fn_path = cx.std_path(&[sym::clone, sym::Clone, sym::clone]);
+    let subcall = |cx: &mut ExtCtxt<'_>, field: &FieldInfo<'_>| {
+        let args = vec![cx.expr_addr_of(field.span, field.self_.clone())];
+        cx.expr_call_global(field.span, fn_path.clone(), args)
+    };
+
+    let vdata;
+    match *substr.fields {
+        Struct(vdata_, ref af) => {
+            ctor_path = cx.path(trait_span, vec![substr.type_ident]);
+            all_fields = af;
+            vdata = vdata_;
+        }
+        EnumMatching(.., variant, ref af) => {
+            ctor_path = cx.path(trait_span, vec![substr.type_ident, variant.ident]);
+            all_fields = af;
+            vdata = &variant.data;
+        }
+        EnumNonMatchingCollapsed(..) => {
+            cx.span_bug(trait_span, &format!("non-matching enum variants in `derive({})`", name,))
+        }
+        StaticEnum(..) | StaticStruct(..) => {
+            cx.span_bug(trait_span, &format!("associated function in `derive({})`", name))
+        }
+    }
+
+    match *vdata {
+        VariantData::Struct(..) => {
+            let fields = all_fields
+                .iter()
+                .map(|field| {
+                    let ident = match field.name {
+                        Some(i) => i,
+                        None => cx.span_bug(
+                            trait_span,
+                            &format!("unnamed field in normal struct in `derive({})`", name,),
+                        ),
+                    };
+                    let call = subcall(cx, field);
+                    cx.field_imm(field.span, ident, call)
+                })
+                .collect::<Vec<_>>();
+
+            cx.expr_struct(trait_span, ctor_path, fields)
+        }
+        VariantData::Tuple(..) => {
+            let subcalls = all_fields.iter().map(|f| subcall(cx, f)).collect();
+            let path = cx.expr_path(ctor_path);
+            cx.expr_call(trait_span, path, subcalls)
+        }
+        VariantData::Unit(..) => cx.expr_path(ctor_path),
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
new file mode 100644
index 00000000000..79f35ad5819
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
@@ -0,0 +1,98 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::path_std;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, GenericArg, MetaItem};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand_deriving_eq(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let inline = cx.meta_word(span, sym::inline);
+    let hidden = rustc_ast::attr::mk_nested_word_item(Ident::new(sym::hidden, span));
+    let doc = rustc_ast::attr::mk_list_item(Ident::new(sym::doc, span), vec![hidden]);
+    let attrs = vec![cx.attribute(inline), cx.attribute(doc)];
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: path_std!(cmp::Eq),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: true,
+        methods: vec![MethodDef {
+            name: sym::assert_receiver_is_total_eq,
+            generics: Bounds::empty(),
+            explicit_self: borrowed_explicit_self(),
+            args: vec![],
+            ret_ty: nil_ty(),
+            attributes: attrs,
+            is_unsafe: false,
+            unify_fieldless_variants: true,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                cs_total_eq_assert(a, b, c)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+
+    super::inject_impl_of_structural_trait(cx, span, item, path_std!(marker::StructuralEq), push);
+
+    trait_def.expand_ext(cx, mitem, item, push, true)
+}
+
+fn cs_total_eq_assert(
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+) -> P<Expr> {
+    fn assert_ty_bounds(
+        cx: &mut ExtCtxt<'_>,
+        stmts: &mut Vec<ast::Stmt>,
+        ty: P<ast::Ty>,
+        span: Span,
+        helper_name: &str,
+    ) {
+        // Generate statement `let _: helper_name<ty>;`,
+        // set the expn ID so we can use the unstable struct.
+        let span = cx.with_def_site_ctxt(span);
+        let assert_path = cx.path_all(
+            span,
+            true,
+            cx.std_path(&[sym::cmp, Symbol::intern(helper_name)]),
+            vec![GenericArg::Type(ty)],
+        );
+        stmts.push(cx.stmt_let_type_only(span, cx.ty_path(assert_path)));
+    }
+    fn process_variant(
+        cx: &mut ExtCtxt<'_>,
+        stmts: &mut Vec<ast::Stmt>,
+        variant: &ast::VariantData,
+    ) {
+        for field in variant.fields() {
+            // let _: AssertParamIsEq<FieldTy>;
+            assert_ty_bounds(cx, stmts, field.ty.clone(), field.span, "AssertParamIsEq");
+        }
+    }
+
+    let mut stmts = Vec::new();
+    match *substr.fields {
+        StaticStruct(vdata, ..) => {
+            process_variant(cx, &mut stmts, vdata);
+        }
+        StaticEnum(enum_def, ..) => {
+            for variant in &enum_def.variants {
+                process_variant(cx, &mut stmts, &variant.data);
+            }
+        }
+        _ => cx.span_bug(trait_span, "unexpected substructure in `derive(Eq)`"),
+    }
+    cx.expr_block(cx.block(trait_span, stmts))
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
new file mode 100644
index 00000000000..c1473e24093
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -0,0 +1,113 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::path_std;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, MetaItem};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{sym, Ident};
+use rustc_span::Span;
+
+pub fn expand_deriving_ord(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let inline = cx.meta_word(span, sym::inline);
+    let attrs = vec![cx.attribute(inline)];
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: path_std!(cmp::Ord),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::cmp,
+            generics: Bounds::empty(),
+            explicit_self: borrowed_explicit_self(),
+            args: vec![(borrowed_self(), sym::other)],
+            ret_ty: Literal(path_std!(cmp::Ordering)),
+            attributes: attrs,
+            is_unsafe: false,
+            unify_fieldless_variants: true,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| cs_cmp(a, b, c))),
+        }],
+        associated_types: Vec::new(),
+    };
+
+    trait_def.expand(cx, mitem, item, push)
+}
+
+pub fn ordering_collapsed(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    self_arg_tags: &[Ident],
+) -> P<ast::Expr> {
+    let lft = cx.expr_ident(span, self_arg_tags[0]);
+    let rgt = cx.expr_addr_of(span, cx.expr_ident(span, self_arg_tags[1]));
+    cx.expr_method_call(span, lft, Ident::new(sym::cmp, span), vec![rgt])
+}
+
+pub fn cs_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
+    let test_id = Ident::new(sym::cmp, span);
+    let equals_path = cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::Equal]));
+
+    let cmp_path = cx.std_path(&[sym::cmp, sym::Ord, sym::cmp]);
+
+    // Builds:
+    //
+    // match ::std::cmp::Ord::cmp(&self_field1, &other_field1) {
+    // ::std::cmp::Ordering::Equal =>
+    // match ::std::cmp::Ord::cmp(&self_field2, &other_field2) {
+    // ::std::cmp::Ordering::Equal => {
+    // ...
+    // }
+    // cmp => cmp
+    // },
+    // cmp => cmp
+    // }
+    //
+    cs_fold(
+        // foldr nests the if-elses correctly, leaving the first field
+        // as the outermost one, and the last as the innermost.
+        false,
+        |cx, span, old, self_f, other_fs| {
+            // match new {
+            //     ::std::cmp::Ordering::Equal => old,
+            //     cmp => cmp
+            // }
+
+            let new = {
+                let other_f = match other_fs {
+                    [o_f] => o_f,
+                    _ => cx.span_bug(span, "not exactly 2 arguments in `derive(Ord)`"),
+                };
+
+                let args =
+                    vec![cx.expr_addr_of(span, self_f), cx.expr_addr_of(span, other_f.clone())];
+
+                cx.expr_call_global(span, cmp_path.clone(), args)
+            };
+
+            let eq_arm = cx.arm(span, cx.pat_path(span, equals_path.clone()), old);
+            let neq_arm = cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
+
+            cx.expr_match(span, new, vec![eq_arm, neq_arm])
+        },
+        cx.expr_path(equals_path.clone()),
+        Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
+            if self_args.len() != 2 {
+                cx.span_bug(span, "not exactly 2 arguments in `derive(Ord)`")
+            } else {
+                ordering_collapsed(cx, span, tag_tuple)
+            }
+        }),
+        cx,
+        span,
+        substr,
+    )
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
new file mode 100644
index 00000000000..8e9f15743cc
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -0,0 +1,112 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::{path_local, path_std};
+
+use rustc_ast::ptr::P;
+use rustc_ast::{BinOpKind, Expr, MetaItem};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+
+pub fn expand_deriving_partial_eq(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    // structures are equal if all fields are equal, and non equal, if
+    // any fields are not equal or if the enum variants are different
+    fn cs_op(
+        cx: &mut ExtCtxt<'_>,
+        span: Span,
+        substr: &Substructure<'_>,
+        op: BinOpKind,
+        combiner: BinOpKind,
+        base: bool,
+    ) -> P<Expr> {
+        let op = |cx: &mut ExtCtxt<'_>, span: Span, self_f: P<Expr>, other_fs: &[P<Expr>]| {
+            let other_f = match other_fs {
+                [o_f] => o_f,
+                _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialEq)`"),
+            };
+
+            cx.expr_binary(span, op, self_f, other_f.clone())
+        };
+
+        cs_fold1(
+            true, // use foldl
+            |cx, span, subexpr, self_f, other_fs| {
+                let eq = op(cx, span, self_f, other_fs);
+                cx.expr_binary(span, combiner, subexpr, eq)
+            },
+            |cx, args| {
+                match args {
+                    Some((span, self_f, other_fs)) => {
+                        // Special-case the base case to generate cleaner code.
+                        op(cx, span, self_f, other_fs)
+                    }
+                    None => cx.expr_bool(span, base),
+                }
+            },
+            Box::new(|cx, span, _, _| cx.expr_bool(span, !base)),
+            cx,
+            span,
+            substr,
+        )
+    }
+
+    fn cs_eq(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
+        cs_op(cx, span, substr, BinOpKind::Eq, BinOpKind::And, true)
+    }
+    fn cs_ne(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
+        cs_op(cx, span, substr, BinOpKind::Ne, BinOpKind::Or, false)
+    }
+
+    macro_rules! md {
+        ($name:expr, $f:ident) => {{
+            let inline = cx.meta_word(span, sym::inline);
+            let attrs = vec![cx.attribute(inline)];
+            MethodDef {
+                name: $name,
+                generics: Bounds::empty(),
+                explicit_self: borrowed_explicit_self(),
+                args: vec![(borrowed_self(), sym::other)],
+                ret_ty: Literal(path_local!(bool)),
+                attributes: attrs,
+                is_unsafe: false,
+                unify_fieldless_variants: true,
+                combine_substructure: combine_substructure(Box::new(|a, b, c| $f(a, b, c))),
+            }
+        }};
+    }
+
+    super::inject_impl_of_structural_trait(
+        cx,
+        span,
+        item,
+        path_std!(marker::StructuralPartialEq),
+        push,
+    );
+
+    // avoid defining `ne` if we can
+    // c-like enums, enums without any fields and structs without fields
+    // can safely define only `eq`.
+    let mut methods = vec![md!(sym::eq, cs_eq)];
+    if !is_type_without_fields(item) {
+        methods.push(md!(sym::ne, cs_ne));
+    }
+
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: path_std!(cmp::PartialEq),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods,
+        associated_types: Vec::new(),
+    };
+    trait_def.expand(cx, mitem, item, push)
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
new file mode 100644
index 00000000000..21174ca4c8b
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -0,0 +1,302 @@
+pub use OrderingOp::*;
+
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::{path_local, path_std, pathvec_std};
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, BinOpKind, Expr, MetaItem};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand_deriving_partial_ord(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    macro_rules! md {
+        ($name:expr, $op:expr, $equal:expr) => {{
+            let inline = cx.meta_word(span, sym::inline);
+            let attrs = vec![cx.attribute(inline)];
+            MethodDef {
+                name: $name,
+                generics: Bounds::empty(),
+                explicit_self: borrowed_explicit_self(),
+                args: vec![(borrowed_self(), sym::other)],
+                ret_ty: Literal(path_local!(bool)),
+                attributes: attrs,
+                is_unsafe: false,
+                unify_fieldless_variants: true,
+                combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
+                    cs_op($op, $equal, cx, span, substr)
+                })),
+            }
+        }};
+    }
+
+    let ordering_ty = Literal(path_std!(cmp::Ordering));
+    let ret_ty = Literal(Path::new_(
+        pathvec_std!(option::Option),
+        None,
+        vec![Box::new(ordering_ty)],
+        PathKind::Std,
+    ));
+
+    let inline = cx.meta_word(span, sym::inline);
+    let attrs = vec![cx.attribute(inline)];
+
+    let partial_cmp_def = MethodDef {
+        name: sym::partial_cmp,
+        generics: Bounds::empty(),
+        explicit_self: borrowed_explicit_self(),
+        args: vec![(borrowed_self(), sym::other)],
+        ret_ty,
+        attributes: attrs,
+        is_unsafe: false,
+        unify_fieldless_variants: true,
+        combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
+            cs_partial_cmp(cx, span, substr)
+        })),
+    };
+
+    // avoid defining extra methods if we can
+    // c-like enums, enums without any fields and structs without fields
+    // can safely define only `partial_cmp`.
+    let methods = if is_type_without_fields(item) {
+        vec![partial_cmp_def]
+    } else {
+        vec![
+            partial_cmp_def,
+            md!(sym::lt, true, false),
+            md!(sym::le, true, true),
+            md!(sym::gt, false, false),
+            md!(sym::ge, false, true),
+        ]
+    };
+
+    let trait_def = TraitDef {
+        span,
+        attributes: vec![],
+        path: path_std!(cmp::PartialOrd),
+        additional_bounds: vec![],
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods,
+        associated_types: Vec::new(),
+    };
+    trait_def.expand(cx, mitem, item, push)
+}
+
+#[derive(Copy, Clone)]
+pub enum OrderingOp {
+    PartialCmpOp,
+    LtOp,
+    LeOp,
+    GtOp,
+    GeOp,
+}
+
+pub fn some_ordering_collapsed(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    op: OrderingOp,
+    self_arg_tags: &[Ident],
+) -> P<ast::Expr> {
+    let lft = cx.expr_ident(span, self_arg_tags[0]);
+    let rgt = cx.expr_addr_of(span, cx.expr_ident(span, self_arg_tags[1]));
+    let op_sym = match op {
+        PartialCmpOp => sym::partial_cmp,
+        LtOp => sym::lt,
+        LeOp => sym::le,
+        GtOp => sym::gt,
+        GeOp => sym::ge,
+    };
+    cx.expr_method_call(span, lft, Ident::new(op_sym, span), vec![rgt])
+}
+
+pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
+    let test_id = Ident::new(sym::cmp, span);
+    let ordering = cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::Equal]));
+    let ordering_expr = cx.expr_path(ordering.clone());
+    let equals_expr = cx.expr_some(span, ordering_expr);
+
+    let partial_cmp_path = cx.std_path(&[sym::cmp, sym::PartialOrd, sym::partial_cmp]);
+
+    // Builds:
+    //
+    // match ::std::cmp::PartialOrd::partial_cmp(&self_field1, &other_field1) {
+    // ::std::option::Option::Some(::std::cmp::Ordering::Equal) =>
+    // match ::std::cmp::PartialOrd::partial_cmp(&self_field2, &other_field2) {
+    // ::std::option::Option::Some(::std::cmp::Ordering::Equal) => {
+    // ...
+    // }
+    // cmp => cmp
+    // },
+    // cmp => cmp
+    // }
+    //
+    cs_fold(
+        // foldr nests the if-elses correctly, leaving the first field
+        // as the outermost one, and the last as the innermost.
+        false,
+        |cx, span, old, self_f, other_fs| {
+            // match new {
+            //     Some(::std::cmp::Ordering::Equal) => old,
+            //     cmp => cmp
+            // }
+
+            let new = {
+                let other_f = match other_fs {
+                    [o_f] => o_f,
+                    _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
+                };
+
+                let args =
+                    vec![cx.expr_addr_of(span, self_f), cx.expr_addr_of(span, other_f.clone())];
+
+                cx.expr_call_global(span, partial_cmp_path.clone(), args)
+            };
+
+            let eq_arm = cx.arm(span, cx.pat_some(span, cx.pat_path(span, ordering.clone())), old);
+            let neq_arm = cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
+
+            cx.expr_match(span, new, vec![eq_arm, neq_arm])
+        },
+        equals_expr,
+        Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
+            if self_args.len() != 2 {
+                cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
+            } else {
+                some_ordering_collapsed(cx, span, PartialCmpOp, tag_tuple)
+            }
+        }),
+        cx,
+        span,
+        substr,
+    )
+}
+
+/// Strict inequality.
+fn cs_op(
+    less: bool,
+    inclusive: bool,
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    substr: &Substructure<'_>,
+) -> P<Expr> {
+    let ordering_path = |cx: &mut ExtCtxt<'_>, name: &str| {
+        cx.expr_path(
+            cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, Symbol::intern(name)])),
+        )
+    };
+
+    let par_cmp = |cx: &mut ExtCtxt<'_>, span, self_f: P<Expr>, other_fs: &[P<Expr>], default| {
+        let other_f = match other_fs {
+            [o_f] => o_f,
+            _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
+        };
+
+        // `PartialOrd::partial_cmp(self.fi, other.fi)`
+        let cmp_path = cx.expr_path(
+            cx.path_global(span, cx.std_path(&[sym::cmp, sym::PartialOrd, sym::partial_cmp])),
+        );
+        let cmp = cx.expr_call(
+            span,
+            cmp_path,
+            vec![cx.expr_addr_of(span, self_f), cx.expr_addr_of(span, other_f.clone())],
+        );
+
+        let default = ordering_path(cx, default);
+        // `Option::unwrap_or(_, Ordering::Equal)`
+        let unwrap_path = cx.expr_path(
+            cx.path_global(span, cx.std_path(&[sym::option, sym::Option, sym::unwrap_or])),
+        );
+        cx.expr_call(span, unwrap_path, vec![cmp, default])
+    };
+
+    let fold = cs_fold1(
+        false, // need foldr
+        |cx, span, subexpr, self_f, other_fs| {
+            // build up a series of `partial_cmp`s from the inside
+            // out (hence foldr) to get lexical ordering, i.e., for op ==
+            // `ast::lt`
+            //
+            // ```
+            // Ordering::then_with(
+            //    Option::unwrap_or(
+            //        PartialOrd::partial_cmp(self.f1, other.f1), Ordering::Equal)
+            //    ),
+            //    Option::unwrap_or(
+            //        PartialOrd::partial_cmp(self.f2, other.f2), Ordering::Greater)
+            //    )
+            // )
+            // == Ordering::Less
+            // ```
+            //
+            // and for op ==
+            // `ast::le`
+            //
+            // ```
+            // Ordering::then_with(
+            //    Option::unwrap_or(
+            //        PartialOrd::partial_cmp(self.f1, other.f1), Ordering::Equal)
+            //    ),
+            //    Option::unwrap_or(
+            //        PartialOrd::partial_cmp(self.f2, other.f2), Ordering::Greater)
+            //    )
+            // )
+            // != Ordering::Greater
+            // ```
+            //
+            // The optimiser should remove the redundancy. We explicitly
+            // get use the binops to avoid auto-deref dereferencing too many
+            // layers of pointers, if the type includes pointers.
+
+            // `Option::unwrap_or(PartialOrd::partial_cmp(self.fi, other.fi), Ordering::Equal)`
+            let par_cmp = par_cmp(cx, span, self_f, other_fs, "Equal");
+
+            // `Ordering::then_with(Option::unwrap_or(..), ..)`
+            let then_with_path = cx.expr_path(
+                cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::then_with])),
+            );
+            cx.expr_call(span, then_with_path, vec![par_cmp, cx.lambda0(span, subexpr)])
+        },
+        |cx, args| match args {
+            Some((span, self_f, other_fs)) => {
+                let opposite = if less { "Greater" } else { "Less" };
+                par_cmp(cx, span, self_f, other_fs, opposite)
+            }
+            None => cx.expr_bool(span, inclusive),
+        },
+        Box::new(|cx, span, (self_args, tag_tuple), _non_self_args| {
+            if self_args.len() != 2 {
+                cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`")
+            } else {
+                let op = match (less, inclusive) {
+                    (false, false) => GtOp,
+                    (false, true) => GeOp,
+                    (true, false) => LtOp,
+                    (true, true) => LeOp,
+                };
+                some_ordering_collapsed(cx, span, op, tag_tuple)
+            }
+        }),
+        cx,
+        span,
+        substr,
+    );
+
+    match *substr.fields {
+        EnumMatching(.., ref all_fields) | Struct(.., ref all_fields) if !all_fields.is_empty() => {
+            let ordering = ordering_path(cx, if less ^ inclusive { "Less" } else { "Greater" });
+            let comp_op = if inclusive { BinOpKind::Ne } else { BinOpKind::Eq };
+
+            cx.expr_binary(span, comp_op, fold, ordering)
+        }
+        _ => fold,
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
new file mode 100644
index 00000000000..120e859f2b1
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -0,0 +1,137 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::path_std;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, MetaItem};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{sym, Ident};
+use rustc_span::{Span, DUMMY_SP};
+
+pub fn expand_deriving_debug(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    // &mut ::std::fmt::Formatter
+    let fmtr =
+        Ptr(Box::new(Literal(path_std!(fmt::Formatter))), Borrowed(None, ast::Mutability::Mut));
+
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: path_std!(fmt::Debug),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::fmt,
+            generics: Bounds::empty(),
+            explicit_self: borrowed_explicit_self(),
+            args: vec![(fmtr, sym::f)],
+            ret_ty: Literal(path_std!(fmt::Result)),
+            attributes: Vec::new(),
+            is_unsafe: false,
+            unify_fieldless_variants: false,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                show_substructure(a, b, c)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+    trait_def.expand(cx, mitem, item, push)
+}
+
+/// We use the debug builders to do the heavy lifting here
+fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
+    // build fmt.debug_struct(<name>).field(<fieldname>, &<fieldval>)....build()
+    // or fmt.debug_tuple(<name>).field(&<fieldval>)....build()
+    // based on the "shape".
+    let (ident, vdata, fields) = match substr.fields {
+        Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
+        EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
+        EnumNonMatchingCollapsed(..) | StaticStruct(..) | StaticEnum(..) => {
+            cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
+        }
+    };
+
+    // We want to make sure we have the ctxt set so that we can use unstable methods
+    let span = cx.with_def_site_ctxt(span);
+    let name = cx.expr_lit(span, ast::LitKind::Str(ident.name, ast::StrStyle::Cooked));
+    let builder = Ident::new(sym::debug_trait_builder, span);
+    let builder_expr = cx.expr_ident(span, builder);
+
+    let fmt = substr.nonself_args[0].clone();
+
+    let mut stmts = vec![];
+    match vdata {
+        ast::VariantData::Tuple(..) | ast::VariantData::Unit(..) => {
+            // tuple struct/"normal" variant
+            let expr =
+                cx.expr_method_call(span, fmt, Ident::new(sym::debug_tuple, span), vec![name]);
+            stmts.push(cx.stmt_let(span, true, builder, expr));
+
+            for field in fields {
+                // Use double indirection to make sure this works for unsized types
+                let field = cx.expr_addr_of(field.span, field.self_.clone());
+                let field = cx.expr_addr_of(field.span, field);
+
+                let expr = cx.expr_method_call(
+                    span,
+                    builder_expr.clone(),
+                    Ident::new(sym::field, span),
+                    vec![field],
+                );
+
+                // Use `let _ = expr;` to avoid triggering the
+                // unused_results lint.
+                stmts.push(stmt_let_underscore(cx, span, expr));
+            }
+        }
+        ast::VariantData::Struct(..) => {
+            // normal struct/struct variant
+            let expr =
+                cx.expr_method_call(span, fmt, Ident::new(sym::debug_struct, span), vec![name]);
+            stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
+
+            for field in fields {
+                let name = cx.expr_lit(
+                    field.span,
+                    ast::LitKind::Str(field.name.unwrap().name, ast::StrStyle::Cooked),
+                );
+
+                // Use double indirection to make sure this works for unsized types
+                let field = cx.expr_addr_of(field.span, field.self_.clone());
+                let field = cx.expr_addr_of(field.span, field);
+                let expr = cx.expr_method_call(
+                    span,
+                    builder_expr.clone(),
+                    Ident::new(sym::field, span),
+                    vec![name, field],
+                );
+                stmts.push(stmt_let_underscore(cx, span, expr));
+            }
+        }
+    }
+
+    let expr = cx.expr_method_call(span, builder_expr, Ident::new(sym::finish, span), vec![]);
+
+    stmts.push(cx.stmt_expr(expr));
+    let block = cx.block(span, stmts);
+    cx.expr_block(block)
+}
+
+fn stmt_let_underscore(cx: &mut ExtCtxt<'_>, sp: Span, expr: P<ast::Expr>) -> ast::Stmt {
+    let local = P(ast::Local {
+        pat: cx.pat_wild(sp),
+        ty: None,
+        init: Some(expr),
+        id: ast::DUMMY_NODE_ID,
+        span: sp,
+        attrs: ast::AttrVec::new(),
+    });
+    ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Local(local), span: sp }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/decodable.rs b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
new file mode 100644
index 00000000000..df69f6c90d8
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
@@ -0,0 +1,223 @@
+//! The compiler code necessary for `#[derive(RustcDecodable)]`. See encodable.rs for more.
+
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::pathvec_std;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, MetaItem, Mutability};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand_deriving_rustc_decodable(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let krate = sym::rustc_serialize;
+    let typaram = sym::__D;
+
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: Path::new_(vec![krate, sym::Decodable], None, vec![], PathKind::Global),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::decode,
+            generics: Bounds {
+                bounds: vec![(
+                    typaram,
+                    vec![Path::new_(vec![krate, sym::Decoder], None, vec![], PathKind::Global)],
+                )],
+            },
+            explicit_self: None,
+            args: vec![(
+                Ptr(Box::new(Literal(Path::new_local(typaram))), Borrowed(None, Mutability::Mut)),
+                sym::d,
+            )],
+            ret_ty: Literal(Path::new_(
+                pathvec_std!(result::Result),
+                None,
+                vec![
+                    Box::new(Self_),
+                    Box::new(Literal(Path::new_(
+                        vec![typaram, sym::Error],
+                        None,
+                        vec![],
+                        PathKind::Local,
+                    ))),
+                ],
+                PathKind::Std,
+            )),
+            attributes: Vec::new(),
+            is_unsafe: false,
+            unify_fieldless_variants: false,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                decodable_substructure(a, b, c, krate)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+
+    trait_def.expand(cx, mitem, item, push)
+}
+
+fn decodable_substructure(
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+    krate: Symbol,
+) -> P<Expr> {
+    let decoder = substr.nonself_args[0].clone();
+    let recurse = vec![
+        Ident::new(krate, trait_span),
+        Ident::new(sym::Decodable, trait_span),
+        Ident::new(sym::decode, trait_span),
+    ];
+    let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
+    // throw an underscore in front to suppress unused variable warnings
+    let blkarg = Ident::new(sym::_d, trait_span);
+    let blkdecoder = cx.expr_ident(trait_span, blkarg);
+
+    match *substr.fields {
+        StaticStruct(_, ref summary) => {
+            let nfields = match *summary {
+                Unnamed(ref fields, _) => fields.len(),
+                Named(ref fields) => fields.len(),
+            };
+            let read_struct_field = Ident::new(sym::read_struct_field, trait_span);
+
+            let path = cx.path_ident(trait_span, substr.type_ident);
+            let result =
+                decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
+                    cx.expr_try(
+                        span,
+                        cx.expr_method_call(
+                            span,
+                            blkdecoder.clone(),
+                            read_struct_field,
+                            vec![
+                                cx.expr_str(span, name),
+                                cx.expr_usize(span, field),
+                                exprdecode.clone(),
+                            ],
+                        ),
+                    )
+                });
+            let result = cx.expr_ok(trait_span, result);
+            cx.expr_method_call(
+                trait_span,
+                decoder,
+                Ident::new(sym::read_struct, trait_span),
+                vec![
+                    cx.expr_str(trait_span, substr.type_ident.name),
+                    cx.expr_usize(trait_span, nfields),
+                    cx.lambda1(trait_span, result, blkarg),
+                ],
+            )
+        }
+        StaticEnum(_, ref fields) => {
+            let variant = Ident::new(sym::i, trait_span);
+
+            let mut arms = Vec::with_capacity(fields.len() + 1);
+            let mut variants = Vec::with_capacity(fields.len());
+            let rvariant_arg = Ident::new(sym::read_enum_variant_arg, trait_span);
+
+            for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
+                variants.push(cx.expr_str(v_span, ident.name));
+
+                let path = cx.path(trait_span, vec![substr.type_ident, ident]);
+                let decoded =
+                    decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
+                        let idx = cx.expr_usize(span, field);
+                        cx.expr_try(
+                            span,
+                            cx.expr_method_call(
+                                span,
+                                blkdecoder.clone(),
+                                rvariant_arg,
+                                vec![idx, exprdecode.clone()],
+                            ),
+                        )
+                    });
+
+                arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
+            }
+
+            arms.push(cx.arm_unreachable(trait_span));
+
+            let result = cx.expr_ok(
+                trait_span,
+                cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
+            );
+            let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
+            let variant_vec = cx.expr_vec(trait_span, variants);
+            let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
+            let result = cx.expr_method_call(
+                trait_span,
+                blkdecoder,
+                Ident::new(sym::read_enum_variant, trait_span),
+                vec![variant_vec, lambda],
+            );
+            cx.expr_method_call(
+                trait_span,
+                decoder,
+                Ident::new(sym::read_enum, trait_span),
+                vec![
+                    cx.expr_str(trait_span, substr.type_ident.name),
+                    cx.lambda1(trait_span, result, blkarg),
+                ],
+            )
+        }
+        _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
+    }
+}
+
+/// Creates a decoder for a single enum variant/struct:
+/// - `outer_pat_path` is the path to this enum variant/struct
+/// - `getarg` should retrieve the `usize`-th field with name `@str`.
+fn decode_static_fields<F>(
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    outer_pat_path: ast::Path,
+    fields: &StaticFields,
+    mut getarg: F,
+) -> P<Expr>
+where
+    F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
+{
+    match *fields {
+        Unnamed(ref fields, is_tuple) => {
+            let path_expr = cx.expr_path(outer_pat_path);
+            if !is_tuple {
+                path_expr
+            } else {
+                let fields = fields
+                    .iter()
+                    .enumerate()
+                    .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
+                    .collect();
+
+                cx.expr_call(trait_span, path_expr, fields)
+            }
+        }
+        Named(ref fields) => {
+            // use the field's span to get nicer error messages.
+            let fields = fields
+                .iter()
+                .enumerate()
+                .map(|(i, &(ident, span))| {
+                    let arg = getarg(cx, span, ident.name, i);
+                    cx.field_imm(span, ident, arg)
+                })
+                .collect();
+            cx.expr_struct(trait_span, outer_pat_path, fields)
+        }
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
new file mode 100644
index 00000000000..980be3a0050
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -0,0 +1,86 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{Expr, MetaItem};
+use rustc_errors::struct_span_err;
+use rustc_expand::base::{Annotatable, DummyResult, ExtCtxt};
+use rustc_span::symbol::{kw, sym};
+use rustc_span::Span;
+
+pub fn expand_deriving_default(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let inline = cx.meta_word(span, sym::inline);
+    let attrs = vec![cx.attribute(inline)];
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: Path::new(vec![kw::Default, sym::Default]),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: kw::Default,
+            generics: Bounds::empty(),
+            explicit_self: None,
+            args: Vec::new(),
+            ret_ty: Self_,
+            attributes: attrs,
+            is_unsafe: false,
+            unify_fieldless_variants: false,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                default_substructure(a, b, c)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+    trait_def.expand(cx, mitem, item, push)
+}
+
+fn default_substructure(
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+) -> P<Expr> {
+    // Note that `kw::Default` is "default" and `sym::Default` is "Default"!
+    let default_ident = cx.std_path(&[kw::Default, sym::Default, kw::Default]);
+    let default_call = |span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
+
+    match *substr.fields {
+        StaticStruct(_, ref summary) => match *summary {
+            Unnamed(ref fields, is_tuple) => {
+                if !is_tuple {
+                    cx.expr_ident(trait_span, substr.type_ident)
+                } else {
+                    let exprs = fields.iter().map(|sp| default_call(*sp)).collect();
+                    cx.expr_call_ident(trait_span, substr.type_ident, exprs)
+                }
+            }
+            Named(ref fields) => {
+                let default_fields = fields
+                    .iter()
+                    .map(|&(ident, span)| cx.field_imm(span, ident, default_call(span)))
+                    .collect();
+                cx.expr_struct_ident(trait_span, substr.type_ident, default_fields)
+            }
+        },
+        StaticEnum(..) => {
+            struct_span_err!(
+                &cx.sess.parse_sess.span_diagnostic,
+                trait_span,
+                E0665,
+                "`Default` cannot be derived for enums, only structs"
+            )
+            .emit();
+            // let compilation continue
+            DummyResult::raw_expr(trait_span, true)
+        }
+        _ => cx.span_bug(trait_span, "method in `derive(Default)`"),
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/encodable.rs b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
new file mode 100644
index 00000000000..62aa1cbfbf2
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
@@ -0,0 +1,291 @@
+//! The compiler code necessary to implement the `#[derive(RustcEncodable)]`
+//! (and `RustcDecodable`, in `decodable.rs`) extension. The idea here is that
+//! type-defining items may be tagged with
+//! `#[derive(RustcEncodable, RustcDecodable)]`.
+//!
+//! For example, a type like:
+//!
+//! ```
+//! #[derive(RustcEncodable, RustcDecodable)]
+//! struct Node { id: usize }
+//! ```
+//!
+//! would generate two implementations like:
+//!
+//! ```
+//! # struct Node { id: usize }
+//! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
+//!     fn encode(&self, s: &mut S) -> Result<(), E> {
+//!         s.emit_struct("Node", 1, |this| {
+//!             this.emit_struct_field("id", 0, |this| {
+//!                 Encodable::encode(&self.id, this)
+//!                 /* this.emit_usize(self.id) can also be used */
+//!             })
+//!         })
+//!     }
+//! }
+//!
+//! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
+//!     fn decode(d: &mut D) -> Result<Node, E> {
+//!         d.read_struct("Node", 1, |this| {
+//!             match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
+//!                 Ok(id) => Ok(Node { id: id }),
+//!                 Err(e) => Err(e),
+//!             }
+//!         })
+//!     }
+//! }
+//! ```
+//!
+//! Other interesting scenarios are when the item has type parameters or
+//! references other non-built-in types. A type definition like:
+//!
+//! ```
+//! # #[derive(RustcEncodable, RustcDecodable)]
+//! # struct Span;
+//! #[derive(RustcEncodable, RustcDecodable)]
+//! struct Spanned<T> { node: T, span: Span }
+//! ```
+//!
+//! would yield functions like:
+//!
+//! ```
+//! # #[derive(RustcEncodable, RustcDecodable)]
+//! # struct Span;
+//! # struct Spanned<T> { node: T, span: Span }
+//! impl<
+//!     S: Encoder<E>,
+//!     E,
+//!     T: Encodable<S, E>
+//! > Encodable<S, E> for Spanned<T> {
+//!     fn encode(&self, s: &mut S) -> Result<(), E> {
+//!         s.emit_struct("Spanned", 2, |this| {
+//!             this.emit_struct_field("node", 0, |this| self.node.encode(this))
+//!                 .unwrap();
+//!             this.emit_struct_field("span", 1, |this| self.span.encode(this))
+//!         })
+//!     }
+//! }
+//!
+//! impl<
+//!     D: Decoder<E>,
+//!     E,
+//!     T: Decodable<D, E>
+//! > Decodable<D, E> for Spanned<T> {
+//!     fn decode(d: &mut D) -> Result<Spanned<T>, E> {
+//!         d.read_struct("Spanned", 2, |this| {
+//!             Ok(Spanned {
+//!                 node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
+//!                     .unwrap(),
+//!                 span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
+//!                     .unwrap(),
+//!             })
+//!         })
+//!     }
+//! }
+//! ```
+
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::pathvec_std;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{Expr, ExprKind, MetaItem, Mutability};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand_deriving_rustc_encodable(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let krate = sym::rustc_serialize;
+    let typaram = sym::__S;
+
+    let trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path: Path::new_(vec![krate, sym::Encodable], None, vec![], PathKind::Global),
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::encode,
+            generics: Bounds {
+                bounds: vec![(
+                    typaram,
+                    vec![Path::new_(vec![krate, sym::Encoder], None, vec![], PathKind::Global)],
+                )],
+            },
+            explicit_self: borrowed_explicit_self(),
+            args: vec![(
+                Ptr(Box::new(Literal(Path::new_local(typaram))), Borrowed(None, Mutability::Mut)),
+                // FIXME: we could use `sym::s` here, but making `s` a static
+                // symbol changes the symbol index ordering in a way that makes
+                // ui/lint/rfc-2457-non-ascii-idents/lint-confusable-idents.rs
+                // fail. The linting code should be fixed so that its output
+                // does not depend on the symbol index ordering.
+                Symbol::intern("s"),
+            )],
+            ret_ty: Literal(Path::new_(
+                pathvec_std!(result::Result),
+                None,
+                vec![
+                    Box::new(Tuple(Vec::new())),
+                    Box::new(Literal(Path::new_(
+                        vec![typaram, sym::Error],
+                        None,
+                        vec![],
+                        PathKind::Local,
+                    ))),
+                ],
+                PathKind::Std,
+            )),
+            attributes: Vec::new(),
+            is_unsafe: false,
+            unify_fieldless_variants: false,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                encodable_substructure(a, b, c, krate)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+
+    trait_def.expand(cx, mitem, item, push)
+}
+
+fn encodable_substructure(
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substr: &Substructure<'_>,
+    krate: Symbol,
+) -> P<Expr> {
+    let encoder = substr.nonself_args[0].clone();
+    // throw an underscore in front to suppress unused variable warnings
+    let blkarg = Ident::new(sym::_e, trait_span);
+    let blkencoder = cx.expr_ident(trait_span, blkarg);
+    let fn_path = cx.expr_path(cx.path_global(
+        trait_span,
+        vec![
+            Ident::new(krate, trait_span),
+            Ident::new(sym::Encodable, trait_span),
+            Ident::new(sym::encode, trait_span),
+        ],
+    ));
+
+    match *substr.fields {
+        Struct(_, ref fields) => {
+            let emit_struct_field = Ident::new(sym::emit_struct_field, trait_span);
+            let mut stmts = Vec::new();
+            for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
+                let name = match name {
+                    Some(id) => id.name,
+                    None => Symbol::intern(&format!("_field{}", i)),
+                };
+                let self_ref = cx.expr_addr_of(span, self_.clone());
+                let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
+                let lambda = cx.lambda1(span, enc, blkarg);
+                let call = cx.expr_method_call(
+                    span,
+                    blkencoder.clone(),
+                    emit_struct_field,
+                    vec![cx.expr_str(span, name), cx.expr_usize(span, i), lambda],
+                );
+
+                // last call doesn't need a try!
+                let last = fields.len() - 1;
+                let call = if i != last {
+                    cx.expr_try(span, call)
+                } else {
+                    cx.expr(span, ExprKind::Ret(Some(call)))
+                };
+
+                let stmt = cx.stmt_expr(call);
+                stmts.push(stmt);
+            }
+
+            // unit structs have no fields and need to return Ok()
+            let blk = if stmts.is_empty() {
+                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
+                cx.lambda1(trait_span, ok, blkarg)
+            } else {
+                cx.lambda_stmts_1(trait_span, stmts, blkarg)
+            };
+
+            cx.expr_method_call(
+                trait_span,
+                encoder,
+                Ident::new(sym::emit_struct, trait_span),
+                vec![
+                    cx.expr_str(trait_span, substr.type_ident.name),
+                    cx.expr_usize(trait_span, fields.len()),
+                    blk,
+                ],
+            )
+        }
+
+        EnumMatching(idx, _, variant, ref fields) => {
+            // We're not generating an AST that the borrow checker is expecting,
+            // so we need to generate a unique local variable to take the
+            // mutable loan out on, otherwise we get conflicts which don't
+            // actually exist.
+            let me = cx.stmt_let(trait_span, false, blkarg, encoder);
+            let encoder = cx.expr_ident(trait_span, blkarg);
+            let emit_variant_arg = Ident::new(sym::emit_enum_variant_arg, trait_span);
+            let mut stmts = Vec::new();
+            if !fields.is_empty() {
+                let last = fields.len() - 1;
+                for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
+                    let self_ref = cx.expr_addr_of(span, self_.clone());
+                    let enc =
+                        cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
+                    let lambda = cx.lambda1(span, enc, blkarg);
+                    let call = cx.expr_method_call(
+                        span,
+                        blkencoder.clone(),
+                        emit_variant_arg,
+                        vec![cx.expr_usize(span, i), lambda],
+                    );
+                    let call = if i != last {
+                        cx.expr_try(span, call)
+                    } else {
+                        cx.expr(span, ExprKind::Ret(Some(call)))
+                    };
+                    stmts.push(cx.stmt_expr(call));
+                }
+            } else {
+                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
+                let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
+                stmts.push(cx.stmt_expr(ret_ok));
+            }
+
+            let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
+            let name = cx.expr_str(trait_span, variant.ident.name);
+            let call = cx.expr_method_call(
+                trait_span,
+                blkencoder,
+                Ident::new(sym::emit_enum_variant, trait_span),
+                vec![
+                    name,
+                    cx.expr_usize(trait_span, idx),
+                    cx.expr_usize(trait_span, fields.len()),
+                    blk,
+                ],
+            );
+            let blk = cx.lambda1(trait_span, call, blkarg);
+            let ret = cx.expr_method_call(
+                trait_span,
+                encoder,
+                Ident::new(sym::emit_enum, trait_span),
+                vec![cx.expr_str(trait_span, substr.type_ident.name), blk],
+            );
+            cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
+        }
+
+        _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
new file mode 100644
index 00000000000..849e8b136e1
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -0,0 +1,1757 @@
+//! Some code that abstracts away much of the boilerplate of writing
+//! `derive` instances for traits. Among other things it manages getting
+//! access to the fields of the 4 different sorts of structs and enum
+//! variants, as well as creating the method and impl ast instances.
+//!
+//! Supported features (fairly exhaustive):
+//!
+//! - Methods taking any number of parameters of any type, and returning
+//!   any type, other than vectors, bottom and closures.
+//! - Generating `impl`s for types with type parameters and lifetimes
+//!   (e.g., `Option<T>`), the parameters are automatically given the
+//!   current trait as a bound. (This includes separate type parameters
+//!   and lifetimes for methods.)
+//! - Additional bounds on the type parameters (`TraitDef.additional_bounds`)
+//!
+//! The most important thing for implementors is the `Substructure` and
+//! `SubstructureFields` objects. The latter groups 5 possibilities of the
+//! arguments:
+//!
+//! - `Struct`, when `Self` is a struct (including tuple structs, e.g
+//!   `struct T(i32, char)`).
+//! - `EnumMatching`, when `Self` is an enum and all the arguments are the
+//!   same variant of the enum (e.g., `Some(1)`, `Some(3)` and `Some(4)`)
+//! - `EnumNonMatchingCollapsed` when `Self` is an enum and the arguments
+//!   are not the same variant (e.g., `None`, `Some(1)` and `None`).
+//! - `StaticEnum` and `StaticStruct` for static methods, where the type
+//!   being derived upon is either an enum or struct respectively. (Any
+//!   argument with type Self is just grouped among the non-self
+//!   arguments.)
+//!
+//! In the first two cases, the values from the corresponding fields in
+//! all the arguments are grouped together. For `EnumNonMatchingCollapsed`
+//! this isn't possible (different variants have different fields), so the
+//! fields are inaccessible. (Previous versions of the deriving infrastructure
+//! had a way to expand into code that could access them, at the cost of
+//! generating exponential amounts of code; see issue #15375). There are no
+//! fields with values in the static cases, so these are treated entirely
+//! differently.
+//!
+//! The non-static cases have `Option<ident>` in several places associated
+//! with field `expr`s. This represents the name of the field it is
+//! associated with. It is only not `None` when the associated field has
+//! an identifier in the source code. For example, the `x`s in the
+//! following snippet
+//!
+//! ```rust
+//! # #![allow(dead_code)]
+//! struct A { x : i32 }
+//!
+//! struct B(i32);
+//!
+//! enum C {
+//!     C0(i32),
+//!     C1 { x: i32 }
+//! }
+//! ```
+//!
+//! The `i32`s in `B` and `C0` don't have an identifier, so the
+//! `Option<ident>`s would be `None` for them.
+//!
+//! In the static cases, the structure is summarized, either into the just
+//! spans of the fields or a list of spans and the field idents (for tuple
+//! structs and record structs, respectively), or a list of these, for
+//! enums (one for each variant). For empty struct and empty enum
+//! variants, it is represented as a count of 0.
+//!
+//! # "`cs`" functions
+//!
+//! The `cs_...` functions ("combine substructure) are designed to
+//! make life easier by providing some pre-made recipes for common
+//! threads; mostly calling the function being derived on all the
+//! arguments and then combining them back together in some way (or
+//! letting the user chose that). They are not meant to be the only
+//! way to handle the structures that this code creates.
+//!
+//! # Examples
+//!
+//! The following simplified `PartialEq` is used for in-code examples:
+//!
+//! ```rust
+//! trait PartialEq {
+//!     fn eq(&self, other: &Self) -> bool;
+//! }
+//! impl PartialEq for i32 {
+//!     fn eq(&self, other: &i32) -> bool {
+//!         *self == *other
+//!     }
+//! }
+//! ```
+//!
+//! Some examples of the values of `SubstructureFields` follow, using the
+//! above `PartialEq`, `A`, `B` and `C`.
+//!
+//! ## Structs
+//!
+//! When generating the `expr` for the `A` impl, the `SubstructureFields` is
+//!
+//! ```{.text}
+//! Struct(vec![FieldInfo {
+//!            span: <span of x>
+//!            name: Some(<ident of x>),
+//!            self_: <expr for &self.x>,
+//!            other: vec![<expr for &other.x]
+//!          }])
+//! ```
+//!
+//! For the `B` impl, called with `B(a)` and `B(b)`,
+//!
+//! ```{.text}
+//! Struct(vec![FieldInfo {
+//!           span: <span of `i32`>,
+//!           name: None,
+//!           self_: <expr for &a>
+//!           other: vec![<expr for &b>]
+//!          }])
+//! ```
+//!
+//! ## Enums
+//!
+//! When generating the `expr` for a call with `self == C0(a)` and `other
+//! == C0(b)`, the SubstructureFields is
+//!
+//! ```{.text}
+//! EnumMatching(0, <ast::Variant for C0>,
+//!              vec![FieldInfo {
+//!                 span: <span of i32>
+//!                 name: None,
+//!                 self_: <expr for &a>,
+//!                 other: vec![<expr for &b>]
+//!               }])
+//! ```
+//!
+//! For `C1 {x}` and `C1 {x}`,
+//!
+//! ```{.text}
+//! EnumMatching(1, <ast::Variant for C1>,
+//!              vec![FieldInfo {
+//!                 span: <span of x>
+//!                 name: Some(<ident of x>),
+//!                 self_: <expr for &self.x>,
+//!                 other: vec![<expr for &other.x>]
+//!                }])
+//! ```
+//!
+//! For `C0(a)` and `C1 {x}` ,
+//!
+//! ```{.text}
+//! EnumNonMatchingCollapsed(
+//!     vec![<ident of self>, <ident of __arg_1>],
+//!     &[<ast::Variant for C0>, <ast::Variant for C1>],
+//!     &[<ident for self index value>, <ident of __arg_1 index value>])
+//! ```
+//!
+//! It is the same for when the arguments are flipped to `C1 {x}` and
+//! `C0(a)`; the only difference is what the values of the identifiers
+//! <ident for self index value> and <ident of __arg_1 index value> will
+//! be in the generated code.
+//!
+//! `EnumNonMatchingCollapsed` deliberately provides far less information
+//! than is generally available for a given pair of variants; see #15375
+//! for discussion.
+//!
+//! ## Static
+//!
+//! A static method on the types above would result in,
+//!
+//! ```{.text}
+//! StaticStruct(<ast::VariantData of A>, Named(vec![(<ident of x>, <span of x>)]))
+//!
+//! StaticStruct(<ast::VariantData of B>, Unnamed(vec![<span of x>]))
+//!
+//! StaticEnum(<ast::EnumDef of C>,
+//!            vec![(<ident of C0>, <span of C0>, Unnamed(vec![<span of i32>])),
+//!                 (<ident of C1>, <span of C1>, Named(vec![(<ident of x>, <span of x>)]))])
+//! ```
+
+pub use StaticFields::*;
+pub use SubstructureFields::*;
+
+use std::cell::RefCell;
+use std::iter;
+use std::vec;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, BinOpKind, EnumDef, Expr, Generics, PatKind};
+use rustc_ast::{GenericArg, GenericParamKind, VariantData};
+use rustc_attr as attr;
+use rustc_data_structures::map_in_place::MapInPlace;
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::source_map::respan;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::Span;
+
+use ty::{Bounds, Path, Ptr, PtrTy, Self_, Ty};
+
+use crate::deriving;
+
+pub mod ty;
+
+pub struct TraitDef<'a> {
+    /// The span for the current #[derive(Foo)] header.
+    pub span: Span,
+
+    pub attributes: Vec<ast::Attribute>,
+
+    /// Path of the trait, including any type parameters
+    pub path: Path,
+
+    /// Additional bounds required of any type parameters of the type,
+    /// other than the current trait
+    pub additional_bounds: Vec<Ty>,
+
+    /// Any extra lifetimes and/or bounds, e.g., `D: serialize::Decoder`
+    pub generics: Bounds,
+
+    /// Is it an `unsafe` trait?
+    pub is_unsafe: bool,
+
+    /// Can this trait be derived for unions?
+    pub supports_unions: bool,
+
+    pub methods: Vec<MethodDef<'a>>,
+
+    pub associated_types: Vec<(Ident, Ty)>,
+}
+
+pub struct MethodDef<'a> {
+    /// name of the method
+    pub name: Symbol,
+    /// List of generics, e.g., `R: rand::Rng`
+    pub generics: Bounds,
+
+    /// Whether there is a self argument (outer Option) i.e., whether
+    /// this is a static function, and whether it is a pointer (inner
+    /// Option)
+    pub explicit_self: Option<Option<PtrTy>>,
+
+    /// Arguments other than the self argument
+    pub args: Vec<(Ty, Symbol)>,
+
+    /// Returns type
+    pub ret_ty: Ty,
+
+    pub attributes: Vec<ast::Attribute>,
+
+    // Is it an `unsafe fn`?
+    pub is_unsafe: bool,
+
+    /// Can we combine fieldless variants for enums into a single match arm?
+    pub unify_fieldless_variants: bool,
+
+    pub combine_substructure: RefCell<CombineSubstructureFunc<'a>>,
+}
+
+/// All the data about the data structure/method being derived upon.
+pub struct Substructure<'a> {
+    /// ident of self
+    pub type_ident: Ident,
+    /// ident of the method
+    pub method_ident: Ident,
+    /// dereferenced access to any `Self_` or `Ptr(Self_, _)` arguments
+    pub self_args: &'a [P<Expr>],
+    /// verbatim access to any other arguments
+    pub nonself_args: &'a [P<Expr>],
+    pub fields: &'a SubstructureFields<'a>,
+}
+
+/// Summary of the relevant parts of a struct/enum field.
+pub struct FieldInfo<'a> {
+    pub span: Span,
+    /// None for tuple structs/normal enum variants, Some for normal
+    /// structs/struct enum variants.
+    pub name: Option<Ident>,
+    /// The expression corresponding to this field of `self`
+    /// (specifically, a reference to it).
+    pub self_: P<Expr>,
+    /// The expressions corresponding to references to this field in
+    /// the other `Self` arguments.
+    pub other: Vec<P<Expr>>,
+    /// The attributes on the field
+    pub attrs: &'a [ast::Attribute],
+}
+
+/// Fields for a static method
+pub enum StaticFields {
+    /// Tuple and unit structs/enum variants like this.
+    Unnamed(Vec<Span>, bool /*is tuple*/),
+    /// Normal structs/struct variants.
+    Named(Vec<(Ident, Span)>),
+}
+
+/// A summary of the possible sets of fields.
+pub enum SubstructureFields<'a> {
+    Struct(&'a ast::VariantData, Vec<FieldInfo<'a>>),
+    /// Matching variants of the enum: variant index, variant count, ast::Variant,
+    /// fields: the field name is only non-`None` in the case of a struct
+    /// variant.
+    EnumMatching(usize, usize, &'a ast::Variant, Vec<FieldInfo<'a>>),
+
+    /// Non-matching variants of the enum, but with all state hidden from
+    /// the consequent code. The first component holds `Ident`s for all of
+    /// the `Self` arguments; the second component is a slice of all of the
+    /// variants for the enum itself, and the third component is a list of
+    /// `Ident`s bound to the variant index values for each of the actual
+    /// input `Self` arguments.
+    EnumNonMatchingCollapsed(Vec<Ident>, &'a [ast::Variant], &'a [Ident]),
+
+    /// A static method where `Self` is a struct.
+    StaticStruct(&'a ast::VariantData, StaticFields),
+    /// A static method where `Self` is an enum.
+    StaticEnum(&'a ast::EnumDef, Vec<(Ident, Span, StaticFields)>),
+}
+
+/// Combine the values of all the fields together. The last argument is
+/// all the fields of all the structures.
+pub type CombineSubstructureFunc<'a> =
+    Box<dyn FnMut(&mut ExtCtxt<'_>, Span, &Substructure<'_>) -> P<Expr> + 'a>;
+
+/// Deal with non-matching enum variants. The tuple is a list of
+/// identifiers (one for each `Self` argument, which could be any of the
+/// variants since they have been collapsed together) and the identifiers
+/// holding the variant index value for each of the `Self` arguments. The
+/// last argument is all the non-`Self` args of the method being derived.
+pub type EnumNonMatchCollapsedFunc<'a> =
+    Box<dyn FnMut(&mut ExtCtxt<'_>, Span, (&[Ident], &[Ident]), &[P<Expr>]) -> P<Expr> + 'a>;
+
+pub fn combine_substructure(
+    f: CombineSubstructureFunc<'_>,
+) -> RefCell<CombineSubstructureFunc<'_>> {
+    RefCell::new(f)
+}
+
+/// This method helps to extract all the type parameters referenced from a
+/// type. For a type parameter `<T>`, it looks for either a `TyPath` that
+/// is not global and starts with `T`, or a `TyQPath`.
+fn find_type_parameters(
+    ty: &ast::Ty,
+    ty_param_names: &[Symbol],
+    cx: &ExtCtxt<'_>,
+) -> Vec<P<ast::Ty>> {
+    use rustc_ast::visit;
+
+    struct Visitor<'a, 'b> {
+        cx: &'a ExtCtxt<'b>,
+        ty_param_names: &'a [Symbol],
+        types: Vec<P<ast::Ty>>,
+    }
+
+    impl<'a, 'b> visit::Visitor<'a> for Visitor<'a, 'b> {
+        fn visit_ty(&mut self, ty: &'a ast::Ty) {
+            if let ast::TyKind::Path(_, ref path) = ty.kind {
+                if let Some(segment) = path.segments.first() {
+                    if self.ty_param_names.contains(&segment.ident.name) {
+                        self.types.push(P(ty.clone()));
+                    }
+                }
+            }
+
+            visit::walk_ty(self, ty)
+        }
+
+        fn visit_mac(&mut self, mac: &ast::MacCall) {
+            self.cx.span_err(mac.span(), "`derive` cannot be used on items with type macros");
+        }
+    }
+
+    let mut visitor = Visitor { cx, ty_param_names, types: Vec::new() };
+    visit::Visitor::visit_ty(&mut visitor, ty);
+
+    visitor.types
+}
+
+impl<'a> TraitDef<'a> {
+    pub fn expand(
+        self,
+        cx: &mut ExtCtxt<'_>,
+        mitem: &ast::MetaItem,
+        item: &'a Annotatable,
+        push: &mut dyn FnMut(Annotatable),
+    ) {
+        self.expand_ext(cx, mitem, item, push, false);
+    }
+
+    pub fn expand_ext(
+        self,
+        cx: &mut ExtCtxt<'_>,
+        mitem: &ast::MetaItem,
+        item: &'a Annotatable,
+        push: &mut dyn FnMut(Annotatable),
+        from_scratch: bool,
+    ) {
+        match *item {
+            Annotatable::Item(ref item) => {
+                let is_packed = item.attrs.iter().any(|attr| {
+                    for r in attr::find_repr_attrs(&cx.sess, attr) {
+                        if let attr::ReprPacked(_) = r {
+                            return true;
+                        }
+                    }
+                    false
+                });
+                let has_no_type_params = match item.kind {
+                    ast::ItemKind::Struct(_, ref generics)
+                    | ast::ItemKind::Enum(_, ref generics)
+                    | ast::ItemKind::Union(_, ref generics) => {
+                        !generics.params.iter().any(|param| match param.kind {
+                            ast::GenericParamKind::Type { .. } => true,
+                            _ => false,
+                        })
+                    }
+                    _ => {
+                        // Non-ADT derive is an error, but it should have been
+                        // set earlier; see
+                        // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
+                        // librustc_expand/base.rs:Annotatable::derive_allowed()
+                        return;
+                    }
+                };
+                let container_id = cx.current_expansion.id.expn_data().parent;
+                let always_copy = has_no_type_params && cx.resolver.has_derive_copy(container_id);
+                let use_temporaries = is_packed && always_copy;
+
+                let newitem = match item.kind {
+                    ast::ItemKind::Struct(ref struct_def, ref generics) => self.expand_struct_def(
+                        cx,
+                        &struct_def,
+                        item.ident,
+                        generics,
+                        from_scratch,
+                        use_temporaries,
+                    ),
+                    ast::ItemKind::Enum(ref enum_def, ref generics) => {
+                        // We ignore `use_temporaries` here, because
+                        // `repr(packed)` enums cause an error later on.
+                        //
+                        // This can only cause further compilation errors
+                        // downstream in blatantly illegal code, so it
+                        // is fine.
+                        self.expand_enum_def(cx, enum_def, item.ident, generics, from_scratch)
+                    }
+                    ast::ItemKind::Union(ref struct_def, ref generics) => {
+                        if self.supports_unions {
+                            self.expand_struct_def(
+                                cx,
+                                &struct_def,
+                                item.ident,
+                                generics,
+                                from_scratch,
+                                use_temporaries,
+                            )
+                        } else {
+                            cx.span_err(mitem.span, "this trait cannot be derived for unions");
+                            return;
+                        }
+                    }
+                    _ => unreachable!(),
+                };
+                // Keep the lint attributes of the previous item to control how the
+                // generated implementations are linted
+                let mut attrs = newitem.attrs.clone();
+                attrs.extend(
+                    item.attrs
+                        .iter()
+                        .filter(|a| {
+                            [
+                                sym::allow,
+                                sym::warn,
+                                sym::deny,
+                                sym::forbid,
+                                sym::stable,
+                                sym::unstable,
+                            ]
+                            .contains(&a.name_or_empty())
+                        })
+                        .cloned(),
+                );
+                push(Annotatable::Item(P(ast::Item { attrs, ..(*newitem).clone() })))
+            }
+            _ => {
+                // Non-Item derive is an error, but it should have been
+                // set earlier; see
+                // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
+                // librustc_expand/base.rs:Annotatable::derive_allowed()
+            }
+        }
+    }
+
+    /// Given that we are deriving a trait `DerivedTrait` for a type like:
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// struct Struct<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z> where C: WhereTrait {
+    ///     a: A,
+    ///     b: B::Item,
+    ///     b1: <B as DeclaredTrait>::Item,
+    ///     c1: <C as WhereTrait>::Item,
+    ///     c2: Option<<C as WhereTrait>::Item>,
+    ///     ...
+    /// }
+    /// ```
+    ///
+    /// create an impl like:
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// impl<'a, ..., 'z, A, B: DeclaredTrait, C, ... Z> where
+    ///     C:                       WhereTrait,
+    ///     A: DerivedTrait + B1 + ... + BN,
+    ///     B: DerivedTrait + B1 + ... + BN,
+    ///     C: DerivedTrait + B1 + ... + BN,
+    ///     B::Item:                 DerivedTrait + B1 + ... + BN,
+    ///     <C as WhereTrait>::Item: DerivedTrait + B1 + ... + BN,
+    ///     ...
+    /// {
+    ///     ...
+    /// }
+    /// ```
+    ///
+    /// where B1, ..., BN are the bounds given by `bounds_paths`.'. Z is a phantom type, and
+    /// therefore does not get bound by the derived trait.
+    fn create_derived_impl(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        type_ident: Ident,
+        generics: &Generics,
+        field_tys: Vec<P<ast::Ty>>,
+        methods: Vec<P<ast::AssocItem>>,
+    ) -> P<ast::Item> {
+        let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
+
+        // Transform associated types from `deriving::ty::Ty` into `ast::AssocItem`
+        let associated_types = self.associated_types.iter().map(|&(ident, ref type_def)| {
+            P(ast::AssocItem {
+                id: ast::DUMMY_NODE_ID,
+                span: self.span,
+                ident,
+                vis: respan(self.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
+                attrs: Vec::new(),
+                kind: ast::AssocItemKind::TyAlias(
+                    ast::Defaultness::Final,
+                    Generics::default(),
+                    Vec::new(),
+                    Some(type_def.to_ty(cx, self.span, type_ident, generics)),
+                ),
+                tokens: None,
+            })
+        });
+
+        let Generics { mut params, mut where_clause, span } =
+            self.generics.to_generics(cx, self.span, type_ident, generics);
+
+        // Create the generic parameters
+        params.extend(generics.params.iter().map(|param| match param.kind {
+            GenericParamKind::Lifetime { .. } => param.clone(),
+            GenericParamKind::Type { .. } => {
+                // I don't think this can be moved out of the loop, since
+                // a GenericBound requires an ast id
+                let bounds: Vec<_> =
+                    // extra restrictions on the generics parameters to the
+                    // type being derived upon
+                    self.additional_bounds.iter().map(|p| {
+                        cx.trait_bound(p.to_path(cx, self.span, type_ident, generics))
+                    }).chain(
+                        // require the current trait
+                        iter::once(cx.trait_bound(trait_path.clone()))
+                    ).chain(
+                        // also add in any bounds from the declaration
+                        param.bounds.iter().cloned()
+                    ).collect();
+
+                cx.typaram(self.span, param.ident, vec![], bounds, None)
+            }
+            GenericParamKind::Const { .. } => param.clone(),
+        }));
+
+        // and similarly for where clauses
+        where_clause.predicates.extend(generics.where_clause.predicates.iter().map(|clause| {
+            match *clause {
+                ast::WherePredicate::BoundPredicate(ref wb) => {
+                    ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
+                        span: self.span,
+                        bound_generic_params: wb.bound_generic_params.clone(),
+                        bounded_ty: wb.bounded_ty.clone(),
+                        bounds: wb.bounds.to_vec(),
+                    })
+                }
+                ast::WherePredicate::RegionPredicate(ref rb) => {
+                    ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
+                        span: self.span,
+                        lifetime: rb.lifetime,
+                        bounds: rb.bounds.to_vec(),
+                    })
+                }
+                ast::WherePredicate::EqPredicate(ref we) => {
+                    ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
+                        id: ast::DUMMY_NODE_ID,
+                        span: self.span,
+                        lhs_ty: we.lhs_ty.clone(),
+                        rhs_ty: we.rhs_ty.clone(),
+                    })
+                }
+            }
+        }));
+
+        {
+            // Extra scope required here so ty_params goes out of scope before params is moved
+
+            let mut ty_params = params
+                .iter()
+                .filter_map(|param| match param.kind {
+                    ast::GenericParamKind::Type { .. } => Some(param),
+                    _ => None,
+                })
+                .peekable();
+
+            if ty_params.peek().is_some() {
+                let ty_param_names: Vec<Symbol> =
+                    ty_params.map(|ty_param| ty_param.ident.name).collect();
+
+                for field_ty in field_tys {
+                    let tys = find_type_parameters(&field_ty, &ty_param_names, cx);
+
+                    for ty in tys {
+                        // if we have already handled this type, skip it
+                        if let ast::TyKind::Path(_, ref p) = ty.kind {
+                            if p.segments.len() == 1
+                                && ty_param_names.contains(&p.segments[0].ident.name)
+                            {
+                                continue;
+                            };
+                        }
+                        let mut bounds: Vec<_> = self
+                            .additional_bounds
+                            .iter()
+                            .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                            .collect();
+
+                        // require the current trait
+                        bounds.push(cx.trait_bound(trait_path.clone()));
+
+                        let predicate = ast::WhereBoundPredicate {
+                            span: self.span,
+                            bound_generic_params: Vec::new(),
+                            bounded_ty: ty,
+                            bounds,
+                        };
+
+                        let predicate = ast::WherePredicate::BoundPredicate(predicate);
+                        where_clause.predicates.push(predicate);
+                    }
+                }
+            }
+        }
+
+        let trait_generics = Generics { params, where_clause, span };
+
+        // Create the reference to the trait.
+        let trait_ref = cx.trait_ref(trait_path);
+
+        let self_params: Vec<_> = generics
+            .params
+            .iter()
+            .map(|param| match param.kind {
+                GenericParamKind::Lifetime { .. } => {
+                    GenericArg::Lifetime(cx.lifetime(self.span, param.ident))
+                }
+                GenericParamKind::Type { .. } => {
+                    GenericArg::Type(cx.ty_ident(self.span, param.ident))
+                }
+                GenericParamKind::Const { .. } => {
+                    GenericArg::Const(cx.const_ident(self.span, param.ident))
+                }
+            })
+            .collect();
+
+        // Create the type of `self`.
+        let path = cx.path_all(self.span, false, vec![type_ident], self_params);
+        let self_type = cx.ty_path(path);
+
+        let attr = cx.attribute(cx.meta_word(self.span, sym::automatically_derived));
+        // Just mark it now since we know that it'll end up used downstream
+        cx.sess.mark_attr_used(&attr);
+        let opt_trait_ref = Some(trait_ref);
+        let unused_qual = {
+            let word = rustc_ast::attr::mk_nested_word_item(Ident::new(
+                sym::unused_qualifications,
+                self.span,
+            ));
+            let list = rustc_ast::attr::mk_list_item(Ident::new(sym::allow, self.span), vec![word]);
+            cx.attribute(list)
+        };
+
+        let mut a = vec![attr, unused_qual];
+        a.extend(self.attributes.iter().cloned());
+
+        let unsafety = if self.is_unsafe { ast::Unsafe::Yes(self.span) } else { ast::Unsafe::No };
+
+        cx.item(
+            self.span,
+            Ident::invalid(),
+            a,
+            ast::ItemKind::Impl {
+                unsafety,
+                polarity: ast::ImplPolarity::Positive,
+                defaultness: ast::Defaultness::Final,
+                constness: ast::Const::No,
+                generics: trait_generics,
+                of_trait: opt_trait_ref,
+                self_ty: self_type,
+                items: methods.into_iter().chain(associated_types).collect(),
+            },
+        )
+    }
+
+    fn expand_struct_def(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        struct_def: &'a VariantData,
+        type_ident: Ident,
+        generics: &Generics,
+        from_scratch: bool,
+        use_temporaries: bool,
+    ) -> P<ast::Item> {
+        let field_tys: Vec<P<ast::Ty>> =
+            struct_def.fields().iter().map(|field| field.ty.clone()).collect();
+
+        let methods = self
+            .methods
+            .iter()
+            .map(|method_def| {
+                let (explicit_self, self_args, nonself_args, tys) =
+                    method_def.split_self_nonself_args(cx, self, type_ident, generics);
+
+                let body = if from_scratch || method_def.is_static() {
+                    method_def.expand_static_struct_method_body(
+                        cx,
+                        self,
+                        struct_def,
+                        type_ident,
+                        &self_args[..],
+                        &nonself_args[..],
+                    )
+                } else {
+                    method_def.expand_struct_method_body(
+                        cx,
+                        self,
+                        struct_def,
+                        type_ident,
+                        &self_args[..],
+                        &nonself_args[..],
+                        use_temporaries,
+                    )
+                };
+
+                method_def.create_method(cx, self, type_ident, generics, explicit_self, tys, body)
+            })
+            .collect();
+
+        self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
+    }
+
+    fn expand_enum_def(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        enum_def: &'a EnumDef,
+        type_ident: Ident,
+        generics: &Generics,
+        from_scratch: bool,
+    ) -> P<ast::Item> {
+        let mut field_tys = Vec::new();
+
+        for variant in &enum_def.variants {
+            field_tys.extend(variant.data.fields().iter().map(|field| field.ty.clone()));
+        }
+
+        let methods = self
+            .methods
+            .iter()
+            .map(|method_def| {
+                let (explicit_self, self_args, nonself_args, tys) =
+                    method_def.split_self_nonself_args(cx, self, type_ident, generics);
+
+                let body = if from_scratch || method_def.is_static() {
+                    method_def.expand_static_enum_method_body(
+                        cx,
+                        self,
+                        enum_def,
+                        type_ident,
+                        &self_args[..],
+                        &nonself_args[..],
+                    )
+                } else {
+                    method_def.expand_enum_method_body(
+                        cx,
+                        self,
+                        enum_def,
+                        type_ident,
+                        self_args,
+                        &nonself_args[..],
+                    )
+                };
+
+                method_def.create_method(cx, self, type_ident, generics, explicit_self, tys, body)
+            })
+            .collect();
+
+        self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
+    }
+}
+
+impl<'a> MethodDef<'a> {
+    fn call_substructure_method(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        type_ident: Ident,
+        self_args: &[P<Expr>],
+        nonself_args: &[P<Expr>],
+        fields: &SubstructureFields<'_>,
+    ) -> P<Expr> {
+        let substructure = Substructure {
+            type_ident,
+            method_ident: Ident::new(self.name, trait_.span),
+            self_args,
+            nonself_args,
+            fields,
+        };
+        let mut f = self.combine_substructure.borrow_mut();
+        let f: &mut CombineSubstructureFunc<'_> = &mut *f;
+        f(cx, trait_.span, &substructure)
+    }
+
+    fn get_ret_ty(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        generics: &Generics,
+        type_ident: Ident,
+    ) -> P<ast::Ty> {
+        self.ret_ty.to_ty(cx, trait_.span, type_ident, generics)
+    }
+
+    fn is_static(&self) -> bool {
+        self.explicit_self.is_none()
+    }
+
+    fn split_self_nonself_args(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        type_ident: Ident,
+        generics: &Generics,
+    ) -> (Option<ast::ExplicitSelf>, Vec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
+        let mut self_args = Vec::new();
+        let mut nonself_args = Vec::new();
+        let mut arg_tys = Vec::new();
+        let mut nonstatic = false;
+
+        let ast_explicit_self = self.explicit_self.as_ref().map(|self_ptr| {
+            let (self_expr, explicit_self) = ty::get_explicit_self(cx, trait_.span, self_ptr);
+
+            self_args.push(self_expr);
+            nonstatic = true;
+
+            explicit_self
+        });
+
+        for (ty, name) in self.args.iter() {
+            let ast_ty = ty.to_ty(cx, trait_.span, type_ident, generics);
+            let ident = Ident::new(*name, trait_.span);
+            arg_tys.push((ident, ast_ty));
+
+            let arg_expr = cx.expr_ident(trait_.span, ident);
+
+            match *ty {
+                // for static methods, just treat any Self
+                // arguments as a normal arg
+                Self_ if nonstatic => {
+                    self_args.push(arg_expr);
+                }
+                Ptr(ref ty, _) if (if let Self_ = **ty { true } else { false }) && nonstatic => {
+                    self_args.push(cx.expr_deref(trait_.span, arg_expr))
+                }
+                _ => {
+                    nonself_args.push(arg_expr);
+                }
+            }
+        }
+
+        (ast_explicit_self, self_args, nonself_args, arg_tys)
+    }
+
+    fn create_method(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        type_ident: Ident,
+        generics: &Generics,
+        explicit_self: Option<ast::ExplicitSelf>,
+        arg_types: Vec<(Ident, P<ast::Ty>)>,
+        body: P<Expr>,
+    ) -> P<ast::AssocItem> {
+        // Create the generics that aren't for `Self`.
+        let fn_generics = self.generics.to_generics(cx, trait_.span, type_ident, generics);
+
+        let args = {
+            let self_args = explicit_self.map(|explicit_self| {
+                let ident = Ident::with_dummy_span(kw::SelfLower).with_span_pos(trait_.span);
+                ast::Param::from_self(ast::AttrVec::default(), explicit_self, ident)
+            });
+            let nonself_args =
+                arg_types.into_iter().map(|(name, ty)| cx.param(trait_.span, name, ty));
+            self_args.into_iter().chain(nonself_args).collect()
+        };
+
+        let ret_type = self.get_ret_ty(cx, trait_, generics, type_ident);
+
+        let method_ident = Ident::new(self.name, trait_.span);
+        let fn_decl = cx.fn_decl(args, ast::FnRetTy::Ty(ret_type));
+        let body_block = cx.block_expr(body);
+
+        let unsafety = if self.is_unsafe { ast::Unsafe::Yes(trait_.span) } else { ast::Unsafe::No };
+
+        let trait_lo_sp = trait_.span.shrink_to_lo();
+
+        let sig = ast::FnSig {
+            header: ast::FnHeader { unsafety, ext: ast::Extern::None, ..ast::FnHeader::default() },
+            decl: fn_decl,
+            span: trait_.span,
+        };
+        let def = ast::Defaultness::Final;
+
+        // Create the method.
+        P(ast::AssocItem {
+            id: ast::DUMMY_NODE_ID,
+            attrs: self.attributes.clone(),
+            span: trait_.span,
+            vis: respan(trait_lo_sp, ast::VisibilityKind::Inherited),
+            ident: method_ident,
+            kind: ast::AssocItemKind::Fn(def, sig, fn_generics, Some(body_block)),
+            tokens: None,
+        })
+    }
+
+    /// ```
+    /// #[derive(PartialEq)]
+    /// # struct Dummy;
+    /// struct A { x: i32, y: i32 }
+    ///
+    /// // equivalent to:
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         match *self {
+    ///             A {x: ref __self_0_0, y: ref __self_0_1} => {
+    ///                 match *other {
+    ///                     A {x: ref __self_1_0, y: ref __self_1_1} => {
+    ///                         __self_0_0.eq(__self_1_0) && __self_0_1.eq(__self_1_1)
+    ///                     }
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// // or if A is repr(packed) - note fields are matched by-value
+    /// // instead of by-reference.
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         match *self {
+    ///             A {x: __self_0_0, y: __self_0_1} => {
+    ///                 match other {
+    ///                     A {x: __self_1_0, y: __self_1_1} => {
+    ///                         __self_0_0.eq(&__self_1_0) && __self_0_1.eq(&__self_1_1)
+    ///                     }
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    fn expand_struct_method_body<'b>(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'b>,
+        struct_def: &'b VariantData,
+        type_ident: Ident,
+        self_args: &[P<Expr>],
+        nonself_args: &[P<Expr>],
+        use_temporaries: bool,
+    ) -> P<Expr> {
+        let mut raw_fields = Vec::new(); // Vec<[fields of self],
+        // [fields of next Self arg], [etc]>
+        let mut patterns = Vec::new();
+        for i in 0..self_args.len() {
+            let struct_path = cx.path(trait_.span, vec![type_ident]);
+            let (pat, ident_expr) = trait_.create_struct_pattern(
+                cx,
+                struct_path,
+                struct_def,
+                &format!("__self_{}", i),
+                ast::Mutability::Not,
+                use_temporaries,
+            );
+            patterns.push(pat);
+            raw_fields.push(ident_expr);
+        }
+
+        // transpose raw_fields
+        let fields = if !raw_fields.is_empty() {
+            let mut raw_fields = raw_fields.into_iter().map(|v| v.into_iter());
+            let first_field = raw_fields.next().unwrap();
+            let mut other_fields: Vec<vec::IntoIter<_>> = raw_fields.collect();
+            first_field
+                .map(|(span, opt_id, field, attrs)| FieldInfo {
+                    span,
+                    name: opt_id,
+                    self_: field,
+                    other: other_fields
+                        .iter_mut()
+                        .map(|l| {
+                            let (.., ex, _) = l.next().unwrap();
+                            ex
+                        })
+                        .collect(),
+                    attrs,
+                })
+                .collect()
+        } else {
+            cx.span_bug(trait_.span, "no `self` parameter for method in generic `derive`")
+        };
+
+        // body of the inner most destructuring match
+        let mut body = self.call_substructure_method(
+            cx,
+            trait_,
+            type_ident,
+            self_args,
+            nonself_args,
+            &Struct(struct_def, fields),
+        );
+
+        // make a series of nested matches, to destructure the
+        // structs. This is actually right-to-left, but it shouldn't
+        // matter.
+        for (arg_expr, pat) in self_args.iter().zip(patterns) {
+            body = cx.expr_match(
+                trait_.span,
+                arg_expr.clone(),
+                vec![cx.arm(trait_.span, pat.clone(), body)],
+            )
+        }
+
+        body
+    }
+
+    fn expand_static_struct_method_body(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        struct_def: &VariantData,
+        type_ident: Ident,
+        self_args: &[P<Expr>],
+        nonself_args: &[P<Expr>],
+    ) -> P<Expr> {
+        let summary = trait_.summarise_struct(cx, struct_def);
+
+        self.call_substructure_method(
+            cx,
+            trait_,
+            type_ident,
+            self_args,
+            nonself_args,
+            &StaticStruct(struct_def, summary),
+        )
+    }
+
+    /// ```
+    /// #[derive(PartialEq)]
+    /// # struct Dummy;
+    /// enum A {
+    ///     A1,
+    ///     A2(i32)
+    /// }
+    ///
+    /// // is equivalent to
+    ///
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> ::bool {
+    ///         match (&*self, &*other) {
+    ///             (&A1, &A1) => true,
+    ///             (&A2(ref self_0),
+    ///              &A2(ref __arg_1_0)) => (*self_0).eq(&(*__arg_1_0)),
+    ///             _ => {
+    ///                 let __self_vi = match *self { A1(..) => 0, A2(..) => 1 };
+    ///                 let __arg_1_vi = match *other { A1(..) => 0, A2(..) => 1 };
+    ///                 false
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// (Of course `__self_vi` and `__arg_1_vi` are unused for
+    /// `PartialEq`, and those subcomputations will hopefully be removed
+    /// as their results are unused. The point of `__self_vi` and
+    /// `__arg_1_vi` is for `PartialOrd`; see #15503.)
+    fn expand_enum_method_body<'b>(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'b>,
+        enum_def: &'b EnumDef,
+        type_ident: Ident,
+        self_args: Vec<P<Expr>>,
+        nonself_args: &[P<Expr>],
+    ) -> P<Expr> {
+        self.build_enum_match_tuple(cx, trait_, enum_def, type_ident, self_args, nonself_args)
+    }
+
+    /// Creates a match for a tuple of all `self_args`, where either all
+    /// variants match, or it falls into a catch-all for when one variant
+    /// does not match.
+
+    /// There are N + 1 cases because is a case for each of the N
+    /// variants where all of the variants match, and one catch-all for
+    /// when one does not match.
+
+    /// As an optimization we generate code which checks whether all variants
+    /// match first which makes llvm see that C-like enums can be compiled into
+    /// a simple equality check (for PartialEq).
+
+    /// The catch-all handler is provided access the variant index values
+    /// for each of the self-args, carried in precomputed variables.
+
+    /// ```{.text}
+    /// let __self0_vi = unsafe {
+    ///     std::intrinsics::discriminant_value(&self) };
+    /// let __self1_vi = unsafe {
+    ///     std::intrinsics::discriminant_value(&arg1) };
+    /// let __self2_vi = unsafe {
+    ///     std::intrinsics::discriminant_value(&arg2) };
+    ///
+    /// if __self0_vi == __self1_vi && __self0_vi == __self2_vi && ... {
+    ///     match (...) {
+    ///         (Variant1, Variant1, ...) => Body1
+    ///         (Variant2, Variant2, ...) => Body2,
+    ///         ...
+    ///         _ => ::core::intrinsics::unreachable()
+    ///     }
+    /// }
+    /// else {
+    ///     ... // catch-all remainder can inspect above variant index values.
+    /// }
+    /// ```
+    fn build_enum_match_tuple<'b>(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'b>,
+        enum_def: &'b EnumDef,
+        type_ident: Ident,
+        mut self_args: Vec<P<Expr>>,
+        nonself_args: &[P<Expr>],
+    ) -> P<Expr> {
+        let sp = trait_.span;
+        let variants = &enum_def.variants;
+
+        let self_arg_names = iter::once("__self".to_string())
+            .chain(
+                self_args
+                    .iter()
+                    .enumerate()
+                    .skip(1)
+                    .map(|(arg_count, _self_arg)| format!("__arg_{}", arg_count)),
+            )
+            .collect::<Vec<String>>();
+
+        let self_arg_idents = self_arg_names
+            .iter()
+            .map(|name| Ident::from_str_and_span(name, sp))
+            .collect::<Vec<Ident>>();
+
+        // The `vi_idents` will be bound, solely in the catch-all, to
+        // a series of let statements mapping each self_arg to an int
+        // value corresponding to its discriminant.
+        let vi_idents = self_arg_names
+            .iter()
+            .map(|name| {
+                let vi_suffix = format!("{}_vi", &name[..]);
+                Ident::from_str_and_span(&vi_suffix, trait_.span)
+            })
+            .collect::<Vec<Ident>>();
+
+        // Builds, via callback to call_substructure_method, the
+        // delegated expression that handles the catch-all case,
+        // using `__variants_tuple` to drive logic if necessary.
+        let catch_all_substructure =
+            EnumNonMatchingCollapsed(self_arg_idents, &variants[..], &vi_idents[..]);
+
+        let first_fieldless = variants.iter().find(|v| v.data.fields().is_empty());
+
+        // These arms are of the form:
+        // (Variant1, Variant1, ...) => Body1
+        // (Variant2, Variant2, ...) => Body2
+        // ...
+        // where each tuple has length = self_args.len()
+        let mut match_arms: Vec<ast::Arm> = variants
+            .iter()
+            .enumerate()
+            .filter(|&(_, v)| !(self.unify_fieldless_variants && v.data.fields().is_empty()))
+            .map(|(index, variant)| {
+                let mk_self_pat = |cx: &mut ExtCtxt<'_>, self_arg_name: &str| {
+                    let (p, idents) = trait_.create_enum_variant_pattern(
+                        cx,
+                        type_ident,
+                        variant,
+                        self_arg_name,
+                        ast::Mutability::Not,
+                    );
+                    (cx.pat(sp, PatKind::Ref(p, ast::Mutability::Not)), idents)
+                };
+
+                // A single arm has form (&VariantK, &VariantK, ...) => BodyK
+                // (see "Final wrinkle" note below for why.)
+                let mut subpats = Vec::with_capacity(self_arg_names.len());
+                let mut self_pats_idents = Vec::with_capacity(self_arg_names.len() - 1);
+                let first_self_pat_idents = {
+                    let (p, idents) = mk_self_pat(cx, &self_arg_names[0]);
+                    subpats.push(p);
+                    idents
+                };
+                for self_arg_name in &self_arg_names[1..] {
+                    let (p, idents) = mk_self_pat(cx, &self_arg_name[..]);
+                    subpats.push(p);
+                    self_pats_idents.push(idents);
+                }
+
+                // Here is the pat = `(&VariantK, &VariantK, ...)`
+                let single_pat = cx.pat_tuple(sp, subpats);
+
+                // For the BodyK, we need to delegate to our caller,
+                // passing it an EnumMatching to indicate which case
+                // we are in.
+
+                // All of the Self args have the same variant in these
+                // cases.  So we transpose the info in self_pats_idents
+                // to gather the getter expressions together, in the
+                // form that EnumMatching expects.
+
+                // The transposition is driven by walking across the
+                // arg fields of the variant for the first self pat.
+                let field_tuples = first_self_pat_idents
+                    .into_iter()
+                    .enumerate()
+                    // For each arg field of self, pull out its getter expr ...
+                    .map(|(field_index, (sp, opt_ident, self_getter_expr, attrs))| {
+                        // ... but FieldInfo also wants getter expr
+                        // for matching other arguments of Self type;
+                        // so walk across the *other* self_pats_idents
+                        // and pull out getter for same field in each
+                        // of them (using `field_index` tracked above).
+                        // That is the heart of the transposition.
+                        let others = self_pats_idents
+                            .iter()
+                            .map(|fields| {
+                                let (_, _opt_ident, ref other_getter_expr, _) = fields[field_index];
+
+                                // All Self args have same variant, so
+                                // opt_idents are the same.  (Assert
+                                // here to make it self-evident that
+                                // it is okay to ignore `_opt_ident`.)
+                                assert!(opt_ident == _opt_ident);
+
+                                other_getter_expr.clone()
+                            })
+                            .collect::<Vec<P<Expr>>>();
+
+                        FieldInfo {
+                            span: sp,
+                            name: opt_ident,
+                            self_: self_getter_expr,
+                            other: others,
+                            attrs,
+                        }
+                    })
+                    .collect::<Vec<FieldInfo<'_>>>();
+
+                // Now, for some given VariantK, we have built up
+                // expressions for referencing every field of every
+                // Self arg, assuming all are instances of VariantK.
+                // Build up code associated with such a case.
+                let substructure = EnumMatching(index, variants.len(), variant, field_tuples);
+                let arm_expr = self.call_substructure_method(
+                    cx,
+                    trait_,
+                    type_ident,
+                    &self_args[..],
+                    nonself_args,
+                    &substructure,
+                );
+
+                cx.arm(sp, single_pat, arm_expr)
+            })
+            .collect();
+
+        let default = match first_fieldless {
+            Some(v) if self.unify_fieldless_variants => {
+                // We need a default case that handles the fieldless variants.
+                // The index and actual variant aren't meaningful in this case,
+                // so just use whatever
+                let substructure = EnumMatching(0, variants.len(), v, Vec::new());
+                Some(self.call_substructure_method(
+                    cx,
+                    trait_,
+                    type_ident,
+                    &self_args[..],
+                    nonself_args,
+                    &substructure,
+                ))
+            }
+            _ if variants.len() > 1 && self_args.len() > 1 => {
+                // Since we know that all the arguments will match if we reach
+                // the match expression we add the unreachable intrinsics as the
+                // result of the catch all which should help llvm in optimizing it
+                Some(deriving::call_intrinsic(cx, sp, sym::unreachable, vec![]))
+            }
+            _ => None,
+        };
+        if let Some(arm) = default {
+            match_arms.push(cx.arm(sp, cx.pat_wild(sp), arm));
+        }
+
+        // We will usually need the catch-all after matching the
+        // tuples `(VariantK, VariantK, ...)` for each VariantK of the
+        // enum.  But:
+        //
+        // * when there is only one Self arg, the arms above suffice
+        // (and the deriving we call back into may not be prepared to
+        // handle EnumNonMatchCollapsed), and,
+        //
+        // * when the enum has only one variant, the single arm that
+        // is already present always suffices.
+        //
+        // * In either of the two cases above, if we *did* add a
+        //   catch-all `_` match, it would trigger the
+        //   unreachable-pattern error.
+        //
+        if variants.len() > 1 && self_args.len() > 1 {
+            // Build a series of let statements mapping each self_arg
+            // to its discriminant value.
+            //
+            // i.e., for `enum E<T> { A, B(1), C(T, T) }`, and a deriving
+            // with three Self args, builds three statements:
+            //
+            // ```
+            // let __self0_vi = unsafe {
+            //     std::intrinsics::discriminant_value(&self) };
+            // let __self1_vi = unsafe {
+            //     std::intrinsics::discriminant_value(&arg1) };
+            // let __self2_vi = unsafe {
+            //     std::intrinsics::discriminant_value(&arg2) };
+            // ```
+            let mut index_let_stmts: Vec<ast::Stmt> = Vec::with_capacity(vi_idents.len() + 1);
+
+            // We also build an expression which checks whether all discriminants are equal
+            // discriminant_test = __self0_vi == __self1_vi && __self0_vi == __self2_vi && ...
+            let mut discriminant_test = cx.expr_bool(sp, true);
+
+            let mut first_ident = None;
+            for (&ident, self_arg) in vi_idents.iter().zip(&self_args) {
+                let self_addr = cx.expr_addr_of(sp, self_arg.clone());
+                let variant_value =
+                    deriving::call_intrinsic(cx, sp, sym::discriminant_value, vec![self_addr]);
+                let let_stmt = cx.stmt_let(sp, false, ident, variant_value);
+                index_let_stmts.push(let_stmt);
+
+                match first_ident {
+                    Some(first) => {
+                        let first_expr = cx.expr_ident(sp, first);
+                        let id = cx.expr_ident(sp, ident);
+                        let test = cx.expr_binary(sp, BinOpKind::Eq, first_expr, id);
+                        discriminant_test =
+                            cx.expr_binary(sp, BinOpKind::And, discriminant_test, test)
+                    }
+                    None => {
+                        first_ident = Some(ident);
+                    }
+                }
+            }
+
+            let arm_expr = self.call_substructure_method(
+                cx,
+                trait_,
+                type_ident,
+                &self_args[..],
+                nonself_args,
+                &catch_all_substructure,
+            );
+
+            // Final wrinkle: the self_args are expressions that deref
+            // down to desired places, but we cannot actually deref
+            // them when they are fed as r-values into a tuple
+            // expression; here add a layer of borrowing, turning
+            // `(*self, *__arg_0, ...)` into `(&*self, &*__arg_0, ...)`.
+            self_args.map_in_place(|self_arg| cx.expr_addr_of(sp, self_arg));
+            let match_arg = cx.expr(sp, ast::ExprKind::Tup(self_args));
+
+            // Lastly we create an expression which branches on all discriminants being equal
+            //  if discriminant_test {
+            //      match (...) {
+            //          (Variant1, Variant1, ...) => Body1
+            //          (Variant2, Variant2, ...) => Body2,
+            //          ...
+            //          _ => ::core::intrinsics::unreachable()
+            //      }
+            //  }
+            //  else {
+            //      <delegated expression referring to __self0_vi, et al.>
+            //  }
+            let all_match = cx.expr_match(sp, match_arg, match_arms);
+            let arm_expr = cx.expr_if(sp, discriminant_test, all_match, Some(arm_expr));
+            index_let_stmts.push(cx.stmt_expr(arm_expr));
+            cx.expr_block(cx.block(sp, index_let_stmts))
+        } else if variants.is_empty() {
+            // As an additional wrinkle, For a zero-variant enum A,
+            // currently the compiler
+            // will accept `fn (a: &Self) { match   *a   { } }`
+            // but rejects `fn (a: &Self) { match (&*a,) { } }`
+            // as well as  `fn (a: &Self) { match ( *a,) { } }`
+            //
+            // This means that the strategy of building up a tuple of
+            // all Self arguments fails when Self is a zero variant
+            // enum: rustc rejects the expanded program, even though
+            // the actual code tends to be impossible to execute (at
+            // least safely), according to the type system.
+            //
+            // The most expedient fix for this is to just let the
+            // code fall through to the catch-all.  But even this is
+            // error-prone, since the catch-all as defined above would
+            // generate code like this:
+            //
+            //     _ => { let __self0 = match *self { };
+            //            let __self1 = match *__arg_0 { };
+            //            <catch-all-expr> }
+            //
+            // Which is yields bindings for variables which type
+            // inference cannot resolve to unique types.
+            //
+            // One option to the above might be to add explicit type
+            // annotations.  But the *only* reason to go down that path
+            // would be to try to make the expanded output consistent
+            // with the case when the number of enum variants >= 1.
+            //
+            // That just isn't worth it.  In fact, trying to generate
+            // sensible code for *any* deriving on a zero-variant enum
+            // does not make sense.  But at the same time, for now, we
+            // do not want to cause a compile failure just because the
+            // user happened to attach a deriving to their
+            // zero-variant enum.
+            //
+            // Instead, just generate a failing expression for the
+            // zero variant case, skipping matches and also skipping
+            // delegating back to the end user code entirely.
+            //
+            // (See also #4499 and #12609; note that some of the
+            // discussions there influence what choice we make here;
+            // e.g., if we feature-gate `match x { ... }` when x refers
+            // to an uninhabited type (e.g., a zero-variant enum or a
+            // type holding such an enum), but do not feature-gate
+            // zero-variant enums themselves, then attempting to
+            // derive Debug on such a type could here generate code
+            // that needs the feature gate enabled.)
+
+            deriving::call_intrinsic(cx, sp, sym::unreachable, vec![])
+        } else {
+            // Final wrinkle: the self_args are expressions that deref
+            // down to desired places, but we cannot actually deref
+            // them when they are fed as r-values into a tuple
+            // expression; here add a layer of borrowing, turning
+            // `(*self, *__arg_0, ...)` into `(&*self, &*__arg_0, ...)`.
+            self_args.map_in_place(|self_arg| cx.expr_addr_of(sp, self_arg));
+            let match_arg = cx.expr(sp, ast::ExprKind::Tup(self_args));
+            cx.expr_match(sp, match_arg, match_arms)
+        }
+    }
+
+    fn expand_static_enum_method_body(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        trait_: &TraitDef<'_>,
+        enum_def: &EnumDef,
+        type_ident: Ident,
+        self_args: &[P<Expr>],
+        nonself_args: &[P<Expr>],
+    ) -> P<Expr> {
+        let summary = enum_def
+            .variants
+            .iter()
+            .map(|v| {
+                let sp = v.span.with_ctxt(trait_.span.ctxt());
+                let summary = trait_.summarise_struct(cx, &v.data);
+                (v.ident, sp, summary)
+            })
+            .collect();
+        self.call_substructure_method(
+            cx,
+            trait_,
+            type_ident,
+            self_args,
+            nonself_args,
+            &StaticEnum(enum_def, summary),
+        )
+    }
+}
+
+// general helper methods.
+impl<'a> TraitDef<'a> {
+    fn summarise_struct(&self, cx: &mut ExtCtxt<'_>, struct_def: &VariantData) -> StaticFields {
+        let mut named_idents = Vec::new();
+        let mut just_spans = Vec::new();
+        for field in struct_def.fields() {
+            let sp = field.span.with_ctxt(self.span.ctxt());
+            match field.ident {
+                Some(ident) => named_idents.push((ident, sp)),
+                _ => just_spans.push(sp),
+            }
+        }
+
+        let is_tuple = if let ast::VariantData::Tuple(..) = struct_def { true } else { false };
+        match (just_spans.is_empty(), named_idents.is_empty()) {
+            (false, false) => cx.span_bug(
+                self.span,
+                "a struct with named and unnamed \
+                                          fields in generic `derive`",
+            ),
+            // named fields
+            (_, false) => Named(named_idents),
+            // unnamed fields
+            (false, _) => Unnamed(just_spans, is_tuple),
+            // empty
+            _ => Named(Vec::new()),
+        }
+    }
+
+    fn create_subpatterns(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        field_paths: Vec<Ident>,
+        mutbl: ast::Mutability,
+        use_temporaries: bool,
+    ) -> Vec<P<ast::Pat>> {
+        field_paths
+            .iter()
+            .map(|path| {
+                let binding_mode = if use_temporaries {
+                    ast::BindingMode::ByValue(ast::Mutability::Not)
+                } else {
+                    ast::BindingMode::ByRef(mutbl)
+                };
+                cx.pat(path.span, PatKind::Ident(binding_mode, *path, None))
+            })
+            .collect()
+    }
+
+    fn create_struct_pattern(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        struct_path: ast::Path,
+        struct_def: &'a VariantData,
+        prefix: &str,
+        mutbl: ast::Mutability,
+        use_temporaries: bool,
+    ) -> (P<ast::Pat>, Vec<(Span, Option<Ident>, P<Expr>, &'a [ast::Attribute])>) {
+        let mut paths = Vec::new();
+        let mut ident_exprs = Vec::new();
+        for (i, struct_field) in struct_def.fields().iter().enumerate() {
+            let sp = struct_field.span.with_ctxt(self.span.ctxt());
+            let ident = Ident::from_str_and_span(&format!("{}_{}", prefix, i), self.span);
+            paths.push(ident.with_span_pos(sp));
+            let val = cx.expr_path(cx.path_ident(sp, ident));
+            let val = if use_temporaries { val } else { cx.expr_deref(sp, val) };
+            let val = cx.expr(sp, ast::ExprKind::Paren(val));
+
+            ident_exprs.push((sp, struct_field.ident, val, &struct_field.attrs[..]));
+        }
+
+        let subpats = self.create_subpatterns(cx, paths, mutbl, use_temporaries);
+        let pattern = match *struct_def {
+            VariantData::Struct(..) => {
+                let field_pats = subpats
+                    .into_iter()
+                    .zip(&ident_exprs)
+                    .map(|(pat, &(sp, ident, ..))| {
+                        if ident.is_none() {
+                            cx.span_bug(sp, "a braced struct with unnamed fields in `derive`");
+                        }
+                        ast::FieldPat {
+                            ident: ident.unwrap(),
+                            is_shorthand: false,
+                            attrs: ast::AttrVec::new(),
+                            id: ast::DUMMY_NODE_ID,
+                            span: pat.span.with_ctxt(self.span.ctxt()),
+                            pat,
+                            is_placeholder: false,
+                        }
+                    })
+                    .collect();
+                cx.pat_struct(self.span, struct_path, field_pats)
+            }
+            VariantData::Tuple(..) => cx.pat_tuple_struct(self.span, struct_path, subpats),
+            VariantData::Unit(..) => cx.pat_path(self.span, struct_path),
+        };
+
+        (pattern, ident_exprs)
+    }
+
+    fn create_enum_variant_pattern(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        enum_ident: Ident,
+        variant: &'a ast::Variant,
+        prefix: &str,
+        mutbl: ast::Mutability,
+    ) -> (P<ast::Pat>, Vec<(Span, Option<Ident>, P<Expr>, &'a [ast::Attribute])>) {
+        let sp = variant.span.with_ctxt(self.span.ctxt());
+        let variant_path = cx.path(sp, vec![enum_ident, variant.ident]);
+        let use_temporaries = false; // enums can't be repr(packed)
+        self.create_struct_pattern(cx, variant_path, &variant.data, prefix, mutbl, use_temporaries)
+    }
+}
+
+// helpful premade recipes
+
+pub fn cs_fold_fields<'a, F>(
+    use_foldl: bool,
+    mut f: F,
+    base: P<Expr>,
+    cx: &mut ExtCtxt<'_>,
+    all_fields: &[FieldInfo<'a>],
+) -> P<Expr>
+where
+    F: FnMut(&mut ExtCtxt<'_>, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>,
+{
+    if use_foldl {
+        all_fields
+            .iter()
+            .fold(base, |old, field| f(cx, field.span, old, field.self_.clone(), &field.other))
+    } else {
+        all_fields
+            .iter()
+            .rev()
+            .fold(base, |old, field| f(cx, field.span, old, field.self_.clone(), &field.other))
+    }
+}
+
+pub fn cs_fold_enumnonmatch(
+    mut enum_nonmatch_f: EnumNonMatchCollapsedFunc<'_>,
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substructure: &Substructure<'_>,
+) -> P<Expr> {
+    match *substructure.fields {
+        EnumNonMatchingCollapsed(ref all_args, _, tuple) => {
+            enum_nonmatch_f(cx, trait_span, (&all_args[..], tuple), substructure.nonself_args)
+        }
+        _ => cx.span_bug(trait_span, "cs_fold_enumnonmatch expected an EnumNonMatchingCollapsed"),
+    }
+}
+
+pub fn cs_fold_static(cx: &mut ExtCtxt<'_>, trait_span: Span) -> P<Expr> {
+    cx.span_bug(trait_span, "static function in `derive`")
+}
+
+/// Fold the fields. `use_foldl` controls whether this is done
+/// left-to-right (`true`) or right-to-left (`false`).
+pub fn cs_fold<F>(
+    use_foldl: bool,
+    f: F,
+    base: P<Expr>,
+    enum_nonmatch_f: EnumNonMatchCollapsedFunc<'_>,
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substructure: &Substructure<'_>,
+) -> P<Expr>
+where
+    F: FnMut(&mut ExtCtxt<'_>, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>,
+{
+    match *substructure.fields {
+        EnumMatching(.., ref all_fields) | Struct(_, ref all_fields) => {
+            cs_fold_fields(use_foldl, f, base, cx, all_fields)
+        }
+        EnumNonMatchingCollapsed(..) => {
+            cs_fold_enumnonmatch(enum_nonmatch_f, cx, trait_span, substructure)
+        }
+        StaticEnum(..) | StaticStruct(..) => cs_fold_static(cx, trait_span),
+    }
+}
+
+/// Function to fold over fields, with three cases, to generate more efficient and concise code.
+/// When the `substructure` has grouped fields, there are two cases:
+/// Zero fields: call the base case function with `None` (like the usual base case of `cs_fold`).
+/// One or more fields: call the base case function on the first value (which depends on
+/// `use_fold`), and use that as the base case. Then perform `cs_fold` on the remainder of the
+/// fields.
+/// When the `substructure` is a `EnumNonMatchingCollapsed`, the result of `enum_nonmatch_f`
+/// is returned. Statics may not be folded over.
+/// See `cs_op` in `partial_ord.rs` for a model example.
+pub fn cs_fold1<F, B>(
+    use_foldl: bool,
+    f: F,
+    mut b: B,
+    enum_nonmatch_f: EnumNonMatchCollapsedFunc<'_>,
+    cx: &mut ExtCtxt<'_>,
+    trait_span: Span,
+    substructure: &Substructure<'_>,
+) -> P<Expr>
+where
+    F: FnMut(&mut ExtCtxt<'_>, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>,
+    B: FnMut(&mut ExtCtxt<'_>, Option<(Span, P<Expr>, &[P<Expr>])>) -> P<Expr>,
+{
+    match *substructure.fields {
+        EnumMatching(.., ref all_fields) | Struct(_, ref all_fields) => {
+            let (base, all_fields) = match (all_fields.is_empty(), use_foldl) {
+                (false, true) => {
+                    let field = &all_fields[0];
+                    let args = (field.span, field.self_.clone(), &field.other[..]);
+                    (b(cx, Some(args)), &all_fields[1..])
+                }
+                (false, false) => {
+                    let idx = all_fields.len() - 1;
+                    let field = &all_fields[idx];
+                    let args = (field.span, field.self_.clone(), &field.other[..]);
+                    (b(cx, Some(args)), &all_fields[..idx])
+                }
+                (true, _) => (b(cx, None), &all_fields[..]),
+            };
+
+            cs_fold_fields(use_foldl, f, base, cx, all_fields)
+        }
+        EnumNonMatchingCollapsed(..) => {
+            cs_fold_enumnonmatch(enum_nonmatch_f, cx, trait_span, substructure)
+        }
+        StaticEnum(..) | StaticStruct(..) => cs_fold_static(cx, trait_span),
+    }
+}
+
+/// Returns `true` if the type has no value fields
+/// (for an enum, no variant has any fields)
+pub fn is_type_without_fields(item: &Annotatable) -> bool {
+    if let Annotatable::Item(ref item) = *item {
+        match item.kind {
+            ast::ItemKind::Enum(ref enum_def, _) => {
+                enum_def.variants.iter().all(|v| v.data.fields().is_empty())
+            }
+            ast::ItemKind::Struct(ref variant_data, _) => variant_data.fields().is_empty(),
+            _ => false,
+        }
+    } else {
+        false
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
new file mode 100644
index 00000000000..6b7d0e1f204
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
@@ -0,0 +1,280 @@
+//! A mini version of ast::Ty, which is easier to use, and features an explicit `Self` type to use
+//! when specifying impls to be derived.
+
+pub use PtrTy::*;
+pub use Ty::*;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Expr, GenericArg, GenericParamKind, Generics, SelfKind};
+use rustc_expand::base::ExtCtxt;
+use rustc_span::source_map::{respan, DUMMY_SP};
+use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_span::Span;
+
+/// The types of pointers
+#[derive(Clone)]
+pub enum PtrTy {
+    /// &'lifetime mut
+    Borrowed(Option<Ident>, ast::Mutability),
+    /// *mut
+    #[allow(dead_code)]
+    Raw(ast::Mutability),
+}
+
+/// A path, e.g., `::std::option::Option::<i32>` (global). Has support
+/// for type parameters and a lifetime.
+#[derive(Clone)]
+pub struct Path {
+    path: Vec<Symbol>,
+    lifetime: Option<Ident>,
+    params: Vec<Box<Ty>>,
+    kind: PathKind,
+}
+
+#[derive(Clone)]
+pub enum PathKind {
+    Local,
+    Global,
+    Std,
+}
+
+impl Path {
+    pub fn new(path: Vec<Symbol>) -> Path {
+        Path::new_(path, None, Vec::new(), PathKind::Std)
+    }
+    pub fn new_local(path: Symbol) -> Path {
+        Path::new_(vec![path], None, Vec::new(), PathKind::Local)
+    }
+    pub fn new_(
+        path: Vec<Symbol>,
+        lifetime: Option<Ident>,
+        params: Vec<Box<Ty>>,
+        kind: PathKind,
+    ) -> Path {
+        Path { path, lifetime, params, kind }
+    }
+
+    pub fn to_ty(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> P<ast::Ty> {
+        cx.ty_path(self.to_path(cx, span, self_ty, self_generics))
+    }
+    pub fn to_path(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> ast::Path {
+        let mut idents = self.path.iter().map(|s| Ident::new(*s, span)).collect();
+        let lt = mk_lifetimes(cx, span, &self.lifetime);
+        let tys: Vec<P<ast::Ty>> =
+            self.params.iter().map(|t| t.to_ty(cx, span, self_ty, self_generics)).collect();
+        let params = lt
+            .into_iter()
+            .map(GenericArg::Lifetime)
+            .chain(tys.into_iter().map(GenericArg::Type))
+            .collect();
+
+        match self.kind {
+            PathKind::Global => cx.path_all(span, true, idents, params),
+            PathKind::Local => cx.path_all(span, false, idents, params),
+            PathKind::Std => {
+                let def_site = cx.with_def_site_ctxt(DUMMY_SP);
+                idents.insert(0, Ident::new(kw::DollarCrate, def_site));
+                cx.path_all(span, false, idents, params)
+            }
+        }
+    }
+}
+
+/// A type. Supports pointers, Self, and literals.
+#[derive(Clone)]
+pub enum Ty {
+    Self_,
+    /// &/Box/ Ty
+    Ptr(Box<Ty>, PtrTy),
+    /// `mod::mod::Type<[lifetime], [Params...]>`, including a plain type
+    /// parameter, and things like `i32`
+    Literal(Path),
+    /// includes unit
+    Tuple(Vec<Ty>),
+}
+
+pub fn borrowed_ptrty() -> PtrTy {
+    Borrowed(None, ast::Mutability::Not)
+}
+pub fn borrowed(ty: Box<Ty>) -> Ty {
+    Ptr(ty, borrowed_ptrty())
+}
+
+pub fn borrowed_explicit_self() -> Option<Option<PtrTy>> {
+    Some(Some(borrowed_ptrty()))
+}
+
+pub fn borrowed_self() -> Ty {
+    borrowed(Box::new(Self_))
+}
+
+pub fn nil_ty() -> Ty {
+    Tuple(Vec::new())
+}
+
+fn mk_lifetime(cx: &ExtCtxt<'_>, span: Span, lt: &Option<Ident>) -> Option<ast::Lifetime> {
+    lt.map(|ident| cx.lifetime(span, ident))
+}
+
+fn mk_lifetimes(cx: &ExtCtxt<'_>, span: Span, lt: &Option<Ident>) -> Vec<ast::Lifetime> {
+    mk_lifetime(cx, span, lt).into_iter().collect()
+}
+
+impl Ty {
+    pub fn to_ty(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> P<ast::Ty> {
+        match *self {
+            Ptr(ref ty, ref ptr) => {
+                let raw_ty = ty.to_ty(cx, span, self_ty, self_generics);
+                match *ptr {
+                    Borrowed(ref lt, mutbl) => {
+                        let lt = mk_lifetime(cx, span, lt);
+                        cx.ty_rptr(span, raw_ty, lt, mutbl)
+                    }
+                    Raw(mutbl) => cx.ty_ptr(span, raw_ty, mutbl),
+                }
+            }
+            Literal(ref p) => p.to_ty(cx, span, self_ty, self_generics),
+            Self_ => cx.ty_path(self.to_path(cx, span, self_ty, self_generics)),
+            Tuple(ref fields) => {
+                let ty = ast::TyKind::Tup(
+                    fields.iter().map(|f| f.to_ty(cx, span, self_ty, self_generics)).collect(),
+                );
+                cx.ty(span, ty)
+            }
+        }
+    }
+
+    pub fn to_path(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        generics: &Generics,
+    ) -> ast::Path {
+        match *self {
+            Self_ => {
+                let params: Vec<_> = generics
+                    .params
+                    .iter()
+                    .map(|param| match param.kind {
+                        GenericParamKind::Lifetime { .. } => {
+                            GenericArg::Lifetime(ast::Lifetime { id: param.id, ident: param.ident })
+                        }
+                        GenericParamKind::Type { .. } => {
+                            GenericArg::Type(cx.ty_ident(span, param.ident))
+                        }
+                        GenericParamKind::Const { .. } => {
+                            GenericArg::Const(cx.const_ident(span, param.ident))
+                        }
+                    })
+                    .collect();
+
+                cx.path_all(span, false, vec![self_ty], params)
+            }
+            Literal(ref p) => p.to_path(cx, span, self_ty, generics),
+            Ptr(..) => cx.span_bug(span, "pointer in a path in generic `derive`"),
+            Tuple(..) => cx.span_bug(span, "tuple in a path in generic `derive`"),
+        }
+    }
+}
+
+fn mk_ty_param(
+    cx: &ExtCtxt<'_>,
+    span: Span,
+    name: Symbol,
+    attrs: &[ast::Attribute],
+    bounds: &[Path],
+    self_ident: Ident,
+    self_generics: &Generics,
+) -> ast::GenericParam {
+    let bounds = bounds
+        .iter()
+        .map(|b| {
+            let path = b.to_path(cx, span, self_ident, self_generics);
+            cx.trait_bound(path)
+        })
+        .collect();
+    cx.typaram(span, Ident::new(name, span), attrs.to_owned(), bounds, None)
+}
+
+fn mk_generics(params: Vec<ast::GenericParam>, span: Span) -> Generics {
+    Generics {
+        params,
+        where_clause: ast::WhereClause { has_where_token: false, predicates: Vec::new(), span },
+        span,
+    }
+}
+
+/// Bounds on type parameters.
+#[derive(Clone)]
+pub struct Bounds {
+    pub bounds: Vec<(Symbol, Vec<Path>)>,
+}
+
+impl Bounds {
+    pub fn empty() -> Bounds {
+        Bounds { bounds: Vec::new() }
+    }
+    pub fn to_generics(
+        &self,
+        cx: &ExtCtxt<'_>,
+        span: Span,
+        self_ty: Ident,
+        self_generics: &Generics,
+    ) -> Generics {
+        let generic_params = self
+            .bounds
+            .iter()
+            .map(|t| {
+                let (name, ref bounds) = *t;
+                mk_ty_param(cx, span, name, &[], &bounds, self_ty, self_generics)
+            })
+            .collect();
+
+        mk_generics(generic_params, span)
+    }
+}
+
+pub fn get_explicit_self(
+    cx: &ExtCtxt<'_>,
+    span: Span,
+    self_ptr: &Option<PtrTy>,
+) -> (P<Expr>, ast::ExplicitSelf) {
+    // this constructs a fresh `self` path
+    let self_path = cx.expr_self(span);
+    match *self_ptr {
+        None => (self_path, respan(span, SelfKind::Value(ast::Mutability::Not))),
+        Some(ref ptr) => {
+            let self_ty = respan(
+                span,
+                match *ptr {
+                    Borrowed(ref lt, mutbl) => {
+                        let lt = lt.map(|s| cx.lifetime(span, s));
+                        SelfKind::Region(lt, mutbl)
+                    }
+                    Raw(_) => cx.span_bug(span, "attempted to use *self in deriving definition"),
+                },
+            );
+            let self_expr = cx.expr_deref(span, self_path);
+            (self_expr, self_ty)
+        }
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
new file mode 100644
index 00000000000..868f863b990
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -0,0 +1,89 @@
+use crate::deriving::generic::ty::*;
+use crate::deriving::generic::*;
+use crate::deriving::{self, path_std, pathvec_std};
+
+use rustc_ast::ptr::P;
+use rustc_ast::{Expr, MetaItem, Mutability};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+
+pub fn expand_deriving_hash(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let path = Path::new_(pathvec_std!(hash::Hash), None, vec![], PathKind::Std);
+
+    let typaram = sym::__H;
+
+    let arg = Path::new_local(typaram);
+    let hash_trait_def = TraitDef {
+        span,
+        attributes: Vec::new(),
+        path,
+        additional_bounds: Vec::new(),
+        generics: Bounds::empty(),
+        is_unsafe: false,
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::hash,
+            generics: Bounds { bounds: vec![(typaram, vec![path_std!(hash::Hasher)])] },
+            explicit_self: borrowed_explicit_self(),
+            args: vec![(Ptr(Box::new(Literal(arg)), Borrowed(None, Mutability::Mut)), sym::state)],
+            ret_ty: nil_ty(),
+            attributes: vec![],
+            is_unsafe: false,
+            unify_fieldless_variants: true,
+            combine_substructure: combine_substructure(Box::new(|a, b, c| {
+                hash_substructure(a, b, c)
+            })),
+        }],
+        associated_types: Vec::new(),
+    };
+
+    hash_trait_def.expand(cx, mitem, item, push);
+}
+
+fn hash_substructure(cx: &mut ExtCtxt<'_>, trait_span: Span, substr: &Substructure<'_>) -> P<Expr> {
+    let state_expr = match &substr.nonself_args {
+        &[o_f] => o_f,
+        _ => cx.span_bug(trait_span, "incorrect number of arguments in `derive(Hash)`"),
+    };
+    let call_hash = |span, thing_expr| {
+        let hash_path = {
+            let strs = cx.std_path(&[sym::hash, sym::Hash, sym::hash]);
+
+            cx.expr_path(cx.path_global(span, strs))
+        };
+        let ref_thing = cx.expr_addr_of(span, thing_expr);
+        let expr = cx.expr_call(span, hash_path, vec![ref_thing, state_expr.clone()]);
+        cx.stmt_expr(expr)
+    };
+    let mut stmts = Vec::new();
+
+    let fields = match *substr.fields {
+        Struct(_, ref fs) | EnumMatching(_, 1, .., ref fs) => fs,
+        EnumMatching(.., ref fs) => {
+            let variant_value = deriving::call_intrinsic(
+                cx,
+                trait_span,
+                sym::discriminant_value,
+                vec![cx.expr_self(trait_span)],
+            );
+
+            stmts.push(call_hash(trait_span, variant_value));
+
+            fs
+        }
+        _ => cx.span_bug(trait_span, "impossible substructure in `derive(Hash)`"),
+    };
+
+    stmts.extend(
+        fields.iter().map(|FieldInfo { ref self_, span, .. }| call_hash(*span, self_.clone())),
+    );
+
+    cx.expr_block(cx.block(trait_span, stmts))
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/mod.rs b/compiler/rustc_builtin_macros/src/deriving/mod.rs
new file mode 100644
index 00000000000..7e3fd131d44
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/mod.rs
@@ -0,0 +1,173 @@
+//! The compiler code necessary to implement the `#[derive]` extensions.
+
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::{ItemKind, MetaItem};
+use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::Span;
+
+macro path_local($x:ident) {
+    generic::ty::Path::new_local(sym::$x)
+}
+
+macro pathvec_std($($rest:ident)::+) {{
+    vec![ $( sym::$rest ),+ ]
+}}
+
+macro path_std($($x:tt)*) {
+    generic::ty::Path::new( pathvec_std!( $($x)* ) )
+}
+
+pub mod bounds;
+pub mod clone;
+pub mod debug;
+pub mod decodable;
+pub mod default;
+pub mod encodable;
+pub mod hash;
+
+#[path = "cmp/eq.rs"]
+pub mod eq;
+#[path = "cmp/ord.rs"]
+pub mod ord;
+#[path = "cmp/partial_eq.rs"]
+pub mod partial_eq;
+#[path = "cmp/partial_ord.rs"]
+pub mod partial_ord;
+
+pub mod generic;
+
+crate struct BuiltinDerive(
+    crate fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable)),
+);
+
+impl MultiItemModifier for BuiltinDerive {
+    fn expand(
+        &self,
+        ecx: &mut ExtCtxt<'_>,
+        span: Span,
+        meta_item: &MetaItem,
+        item: Annotatable,
+    ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
+        // FIXME: Built-in derives often forget to give spans contexts,
+        // so we are doing it here in a centralized way.
+        let span = ecx.with_def_site_ctxt(span);
+        let mut items = Vec::new();
+        (self.0)(ecx, span, meta_item, &item, &mut |a| items.push(a));
+        ExpandResult::Ready(items)
+    }
+}
+
+/// Constructs an expression that calls an intrinsic
+fn call_intrinsic(
+    cx: &ExtCtxt<'_>,
+    span: Span,
+    intrinsic: Symbol,
+    args: Vec<P<ast::Expr>>,
+) -> P<ast::Expr> {
+    let span = cx.with_def_site_ctxt(span);
+    let path = cx.std_path(&[sym::intrinsics, intrinsic]);
+    let call = cx.expr_call_global(span, path, args);
+
+    cx.expr_block(P(ast::Block {
+        stmts: vec![cx.stmt_expr(call)],
+        id: ast::DUMMY_NODE_ID,
+        rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
+        span,
+    }))
+}
+
+// Injects `impl<...> Structural for ItemType<...> { }`. In particular,
+// does *not* add `where T: Structural` for parameters `T` in `...`.
+// (That's the main reason we cannot use TraitDef here.)
+fn inject_impl_of_structural_trait(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    item: &Annotatable,
+    structural_path: generic::ty::Path,
+    push: &mut dyn FnMut(Annotatable),
+) {
+    let item = match *item {
+        Annotatable::Item(ref item) => item,
+        _ => {
+            // Non-Item derive is an error, but it should have been
+            // set earlier; see
+            // librustc_expand/expand.rs:MacroExpander::fully_expand_fragment()
+            // librustc_expand/base.rs:Annotatable::derive_allowed()
+            return;
+        }
+    };
+
+    let generics = match item.kind {
+        ItemKind::Struct(_, ref generics) | ItemKind::Enum(_, ref generics) => generics,
+        // Do not inject `impl Structural for Union`. (`PartialEq` does not
+        // support unions, so we will see error downstream.)
+        ItemKind::Union(..) => return,
+        _ => unreachable!(),
+    };
+
+    // Create generics param list for where clauses and impl headers
+    let mut generics = generics.clone();
+
+    // Create the type of `self`.
+    //
+    // in addition, remove defaults from type params (impls cannot have them).
+    let self_params: Vec<_> = generics
+        .params
+        .iter_mut()
+        .map(|param| match &mut param.kind {
+            ast::GenericParamKind::Lifetime => {
+                ast::GenericArg::Lifetime(cx.lifetime(span, param.ident))
+            }
+            ast::GenericParamKind::Type { default } => {
+                *default = None;
+                ast::GenericArg::Type(cx.ty_ident(span, param.ident))
+            }
+            ast::GenericParamKind::Const { ty: _, kw_span: _ } => {
+                ast::GenericArg::Const(cx.const_ident(span, param.ident))
+            }
+        })
+        .collect();
+
+    let type_ident = item.ident;
+
+    let trait_ref = cx.trait_ref(structural_path.to_path(cx, span, type_ident, &generics));
+    let self_type = cx.ty_path(cx.path_all(span, false, vec![type_ident], self_params));
+
+    // It would be nice to also encode constraint `where Self: Eq` (by adding it
+    // onto `generics` cloned above). Unfortunately, that strategy runs afoul of
+    // rust-lang/rust#48214. So we perform that additional check in the compiler
+    // itself, instead of encoding it here.
+
+    // Keep the lint and stability attributes of the original item, to control
+    // how the generated implementation is linted.
+    let mut attrs = Vec::new();
+    attrs.extend(
+        item.attrs
+            .iter()
+            .filter(|a| {
+                [sym::allow, sym::warn, sym::deny, sym::forbid, sym::stable, sym::unstable]
+                    .contains(&a.name_or_empty())
+            })
+            .cloned(),
+    );
+
+    let newitem = cx.item(
+        span,
+        Ident::invalid(),
+        attrs,
+        ItemKind::Impl {
+            unsafety: ast::Unsafe::No,
+            polarity: ast::ImplPolarity::Positive,
+            defaultness: ast::Defaultness::Final,
+            constness: ast::Const::No,
+            generics,
+            of_trait: Some(trait_ref),
+            self_ty: self_type,
+            items: Vec::new(),
+        },
+    );
+
+    push(Annotatable::Item(newitem));
+}
diff --git a/compiler/rustc_builtin_macros/src/env.rs b/compiler/rustc_builtin_macros/src/env.rs
new file mode 100644
index 00000000000..6de12acfb94
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/env.rs
@@ -0,0 +1,93 @@
+// The compiler code necessary to support the env! extension.  Eventually this
+// should all get sucked into either the compiler syntax extension plugin
+// interface.
+//
+
+use rustc_ast::tokenstream::TokenStream;
+use rustc_ast::{self as ast, GenericArg};
+use rustc_expand::base::{self, *};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::Span;
+
+use std::env;
+
+pub fn expand_option_env<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    let var = match get_single_str_from_tts(cx, sp, tts, "option_env!") {
+        None => return DummyResult::any(sp),
+        Some(v) => v,
+    };
+
+    let sp = cx.with_def_site_ctxt(sp);
+    let value = env::var(&var.as_str()).ok().as_deref().map(Symbol::intern);
+    cx.sess.parse_sess.env_depinfo.borrow_mut().insert((Symbol::intern(&var), value));
+    let e = match value {
+        None => {
+            let lt = cx.lifetime(sp, Ident::new(kw::StaticLifetime, sp));
+            cx.expr_path(cx.path_all(
+                sp,
+                true,
+                cx.std_path(&[sym::option, sym::Option, sym::None]),
+                vec![GenericArg::Type(cx.ty_rptr(
+                    sp,
+                    cx.ty_ident(sp, Ident::new(sym::str, sp)),
+                    Some(lt),
+                    ast::Mutability::Not,
+                ))],
+            ))
+        }
+        Some(value) => cx.expr_call_global(
+            sp,
+            cx.std_path(&[sym::option, sym::Option, sym::Some]),
+            vec![cx.expr_str(sp, value)],
+        ),
+    };
+    MacEager::expr(e)
+}
+
+pub fn expand_env<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    let mut exprs = match get_exprs_from_tts(cx, sp, tts) {
+        Some(ref exprs) if exprs.is_empty() => {
+            cx.span_err(sp, "env! takes 1 or 2 arguments");
+            return DummyResult::any(sp);
+        }
+        None => return DummyResult::any(sp),
+        Some(exprs) => exprs.into_iter(),
+    };
+
+    let var = match expr_to_string(cx, exprs.next().unwrap(), "expected string literal") {
+        None => return DummyResult::any(sp),
+        Some((v, _style)) => v,
+    };
+    let msg = match exprs.next() {
+        None => Symbol::intern(&format!("environment variable `{}` not defined", var)),
+        Some(second) => match expr_to_string(cx, second, "expected string literal") {
+            None => return DummyResult::any(sp),
+            Some((s, _style)) => s,
+        },
+    };
+
+    if exprs.next().is_some() {
+        cx.span_err(sp, "env! takes 1 or 2 arguments");
+        return DummyResult::any(sp);
+    }
+
+    let sp = cx.with_def_site_ctxt(sp);
+    let value = env::var(&*var.as_str()).ok().as_deref().map(Symbol::intern);
+    cx.sess.parse_sess.env_depinfo.borrow_mut().insert((var, value));
+    let e = match value {
+        None => {
+            cx.span_err(sp, &msg.as_str());
+            return DummyResult::any(sp);
+        }
+        Some(value) => cx.expr_str(sp, value),
+    };
+    MacEager::expr(e)
+}
diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
new file mode 100644
index 00000000000..373277f525d
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -0,0 +1,1155 @@
+use ArgumentType::*;
+use Position::*;
+
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::{pluralize, Applicability, DiagnosticBuilder};
+use rustc_expand::base::{self, *};
+use rustc_parse_format as parse;
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::{MultiSpan, Span};
+
+use std::borrow::Cow;
+use std::collections::hash_map::Entry;
+
+#[derive(PartialEq)]
+enum ArgumentType {
+    Placeholder(&'static str),
+    Count,
+}
+
+enum Position {
+    Exact(usize),
+    Named(Symbol),
+}
+
+struct Context<'a, 'b> {
+    ecx: &'a mut ExtCtxt<'b>,
+    /// The macro's call site. References to unstable formatting internals must
+    /// use this span to pass the stability checker.
+    macsp: Span,
+    /// The span of the format string literal.
+    fmtsp: Span,
+
+    /// List of parsed argument expressions.
+    /// Named expressions are resolved early, and are appended to the end of
+    /// argument expressions.
+    ///
+    /// Example showing the various data structures in motion:
+    ///
+    /// * Original: `"{foo:o} {:o} {foo:x} {0:x} {1:o} {:x} {1:x} {0:o}"`
+    /// * Implicit argument resolution: `"{foo:o} {0:o} {foo:x} {0:x} {1:o} {1:x} {1:x} {0:o}"`
+    /// * Name resolution: `"{2:o} {0:o} {2:x} {0:x} {1:o} {1:x} {1:x} {0:o}"`
+    /// * `arg_types` (in JSON): `[[0, 1, 0], [0, 1, 1], [0, 1]]`
+    /// * `arg_unique_types` (in simplified JSON): `[["o", "x"], ["o", "x"], ["o", "x"]]`
+    /// * `names` (in JSON): `{"foo": 2}`
+    args: Vec<P<ast::Expr>>,
+    /// Placeholder slot numbers indexed by argument.
+    arg_types: Vec<Vec<usize>>,
+    /// Unique format specs seen for each argument.
+    arg_unique_types: Vec<Vec<ArgumentType>>,
+    /// Map from named arguments to their resolved indices.
+    names: FxHashMap<Symbol, usize>,
+
+    /// The latest consecutive literal strings, or empty if there weren't any.
+    literal: String,
+
+    /// Collection of the compiled `rt::Argument` structures
+    pieces: Vec<P<ast::Expr>>,
+    /// Collection of string literals
+    str_pieces: Vec<P<ast::Expr>>,
+    /// Stays `true` if all formatting parameters are default (as in "{}{}").
+    all_pieces_simple: bool,
+
+    /// Mapping between positional argument references and indices into the
+    /// final generated static argument array. We record the starting indices
+    /// corresponding to each positional argument, and number of references
+    /// consumed so far for each argument, to facilitate correct `Position`
+    /// mapping in `build_piece`. In effect this can be seen as a "flattened"
+    /// version of `arg_unique_types`.
+    ///
+    /// Again with the example described above in docstring for `args`:
+    ///
+    /// * `arg_index_map` (in JSON): `[[0, 1, 0], [2, 3, 3], [4, 5]]`
+    arg_index_map: Vec<Vec<usize>>,
+
+    /// Starting offset of count argument slots.
+    count_args_index_offset: usize,
+
+    /// Count argument slots and tracking data structures.
+    /// Count arguments are separately tracked for de-duplication in case
+    /// multiple references are made to one argument. For example, in this
+    /// format string:
+    ///
+    /// * Original: `"{:.*} {:.foo$} {1:.*} {:.0$}"`
+    /// * Implicit argument resolution: `"{1:.0$} {2:.foo$} {1:.3$} {4:.0$}"`
+    /// * Name resolution: `"{1:.0$} {2:.5$} {1:.3$} {4:.0$}"`
+    /// * `count_positions` (in JSON): `{0: 0, 5: 1, 3: 2}`
+    /// * `count_args`: `vec![Exact(0), Exact(5), Exact(3)]`
+    count_args: Vec<Position>,
+    /// Relative slot numbers for count arguments.
+    count_positions: FxHashMap<usize, usize>,
+    /// Number of count slots assigned.
+    count_positions_count: usize,
+
+    /// Current position of the implicit positional arg pointer, as if it
+    /// still existed in this phase of processing.
+    /// Used only for `all_pieces_simple` tracking in `build_piece`.
+    curarg: usize,
+    /// Current piece being evaluated, used for error reporting.
+    curpiece: usize,
+    /// Keep track of invalid references to positional arguments.
+    invalid_refs: Vec<(usize, usize)>,
+    /// Spans of all the formatting arguments, in order.
+    arg_spans: Vec<Span>,
+    /// All the formatting arguments that have formatting flags set, in order for diagnostics.
+    arg_with_formatting: Vec<parse::FormatSpec<'a>>,
+
+    /// Whether this format string came from a string literal, as opposed to a macro.
+    is_literal: bool,
+}
+
+/// Parses the arguments from the given list of tokens, returning the diagnostic
+/// if there's a parse error so we can continue parsing other format!
+/// expressions.
+///
+/// If parsing succeeds, the return value is:
+///
+/// ```text
+/// Some((fmtstr, parsed arguments, index map for named arguments))
+/// ```
+fn parse_args<'a>(
+    ecx: &mut ExtCtxt<'a>,
+    sp: Span,
+    tts: TokenStream,
+) -> Result<(P<ast::Expr>, Vec<P<ast::Expr>>, FxHashMap<Symbol, usize>), DiagnosticBuilder<'a>> {
+    let mut args = Vec::<P<ast::Expr>>::new();
+    let mut names = FxHashMap::<Symbol, usize>::default();
+
+    let mut p = ecx.new_parser_from_tts(tts);
+
+    if p.token == token::Eof {
+        return Err(ecx.struct_span_err(sp, "requires at least a format string argument"));
+    }
+
+    let fmtstr = p.parse_expr()?;
+    let mut first = true;
+    let mut named = false;
+
+    while p.token != token::Eof {
+        if !p.eat(&token::Comma) {
+            if first {
+                // After `format!(""` we always expect *only* a comma...
+                let mut err = ecx.struct_span_err(p.token.span, "expected token: `,`");
+                err.span_label(p.token.span, "expected `,`");
+                p.maybe_annotate_with_ascription(&mut err, false);
+                return Err(err);
+            } else {
+                // ...after that delegate to `expect` to also include the other expected tokens.
+                let _ = p.expect(&token::Comma)?;
+            }
+        }
+        first = false;
+        if p.token == token::Eof {
+            break;
+        } // accept trailing commas
+        match p.token.ident() {
+            Some((ident, _)) if p.look_ahead(1, |t| *t == token::Eq) => {
+                named = true;
+                p.bump();
+                p.expect(&token::Eq)?;
+                let e = p.parse_expr()?;
+                if let Some(prev) = names.get(&ident.name) {
+                    ecx.struct_span_err(e.span, &format!("duplicate argument named `{}`", ident))
+                        .span_label(args[*prev].span, "previously here")
+                        .span_label(e.span, "duplicate argument")
+                        .emit();
+                    continue;
+                }
+
+                // Resolve names into slots early.
+                // Since all the positional args are already seen at this point
+                // if the input is valid, we can simply append to the positional
+                // args. And remember the names.
+                let slot = args.len();
+                names.insert(ident.name, slot);
+                args.push(e);
+            }
+            _ => {
+                let e = p.parse_expr()?;
+                if named {
+                    let mut err = ecx.struct_span_err(
+                        e.span,
+                        "positional arguments cannot follow named arguments",
+                    );
+                    err.span_label(e.span, "positional arguments must be before named arguments");
+                    for pos in names.values() {
+                        err.span_label(args[*pos].span, "named argument");
+                    }
+                    err.emit();
+                }
+                args.push(e);
+            }
+        }
+    }
+    Ok((fmtstr, args, names))
+}
+
+impl<'a, 'b> Context<'a, 'b> {
+    fn resolve_name_inplace(&self, p: &mut parse::Piece<'_>) {
+        // NOTE: the `unwrap_or` branch is needed in case of invalid format
+        // arguments, e.g., `format_args!("{foo}")`.
+        let lookup = |s: Symbol| *self.names.get(&s).unwrap_or(&0);
+
+        match *p {
+            parse::String(_) => {}
+            parse::NextArgument(ref mut arg) => {
+                if let parse::ArgumentNamed(s) = arg.position {
+                    arg.position = parse::ArgumentIs(lookup(s));
+                }
+                if let parse::CountIsName(s) = arg.format.width {
+                    arg.format.width = parse::CountIsParam(lookup(s));
+                }
+                if let parse::CountIsName(s) = arg.format.precision {
+                    arg.format.precision = parse::CountIsParam(lookup(s));
+                }
+            }
+        }
+    }
+
+    /// Verifies one piece of a parse string, and remembers it if valid.
+    /// All errors are not emitted as fatal so we can continue giving errors
+    /// about this and possibly other format strings.
+    fn verify_piece(&mut self, p: &parse::Piece<'_>) {
+        match *p {
+            parse::String(..) => {}
+            parse::NextArgument(ref arg) => {
+                // width/precision first, if they have implicit positional
+                // parameters it makes more sense to consume them first.
+                self.verify_count(arg.format.width);
+                self.verify_count(arg.format.precision);
+
+                // argument second, if it's an implicit positional parameter
+                // it's written second, so it should come after width/precision.
+                let pos = match arg.position {
+                    parse::ArgumentIs(i) | parse::ArgumentImplicitlyIs(i) => Exact(i),
+                    parse::ArgumentNamed(s) => Named(s),
+                };
+
+                let ty = Placeholder(match &arg.format.ty[..] {
+                    "" => "Display",
+                    "?" => "Debug",
+                    "e" => "LowerExp",
+                    "E" => "UpperExp",
+                    "o" => "Octal",
+                    "p" => "Pointer",
+                    "b" => "Binary",
+                    "x" => "LowerHex",
+                    "X" => "UpperHex",
+                    _ => {
+                        let fmtsp = self.fmtsp;
+                        let sp = arg.format.ty_span.map(|sp| fmtsp.from_inner(sp));
+                        let mut err = self.ecx.struct_span_err(
+                            sp.unwrap_or(fmtsp),
+                            &format!("unknown format trait `{}`", arg.format.ty),
+                        );
+                        err.note(
+                            "the only appropriate formatting traits are:\n\
+                                - ``, which uses the `Display` trait\n\
+                                - `?`, which uses the `Debug` trait\n\
+                                - `e`, which uses the `LowerExp` trait\n\
+                                - `E`, which uses the `UpperExp` trait\n\
+                                - `o`, which uses the `Octal` trait\n\
+                                - `p`, which uses the `Pointer` trait\n\
+                                - `b`, which uses the `Binary` trait\n\
+                                - `x`, which uses the `LowerHex` trait\n\
+                                - `X`, which uses the `UpperHex` trait",
+                        );
+                        if let Some(sp) = sp {
+                            for (fmt, name) in &[
+                                ("", "Display"),
+                                ("?", "Debug"),
+                                ("e", "LowerExp"),
+                                ("E", "UpperExp"),
+                                ("o", "Octal"),
+                                ("p", "Pointer"),
+                                ("b", "Binary"),
+                                ("x", "LowerHex"),
+                                ("X", "UpperHex"),
+                            ] {
+                                // FIXME: rustfix (`run-rustfix`) fails to apply suggestions.
+                                // > "Cannot replace slice of data that was already replaced"
+                                err.tool_only_span_suggestion(
+                                    sp,
+                                    &format!("use the `{}` trait", name),
+                                    (*fmt).to_string(),
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                        }
+                        err.emit();
+                        "<invalid>"
+                    }
+                });
+                self.verify_arg_type(pos, ty);
+                self.curpiece += 1;
+            }
+        }
+    }
+
+    fn verify_count(&mut self, c: parse::Count) {
+        match c {
+            parse::CountImplied | parse::CountIs(..) => {}
+            parse::CountIsParam(i) => {
+                self.verify_arg_type(Exact(i), Count);
+            }
+            parse::CountIsName(s) => {
+                self.verify_arg_type(Named(s), Count);
+            }
+        }
+    }
+
+    fn describe_num_args(&self) -> Cow<'_, str> {
+        match self.args.len() {
+            0 => "no arguments were given".into(),
+            1 => "there is 1 argument".into(),
+            x => format!("there are {} arguments", x).into(),
+        }
+    }
+
+    /// Handle invalid references to positional arguments. Output different
+    /// errors for the case where all arguments are positional and for when
+    /// there are named arguments or numbered positional arguments in the
+    /// format string.
+    fn report_invalid_references(&self, numbered_position_args: bool) {
+        let mut e;
+        let sp = if !self.arg_spans.is_empty() {
+            // Point at the formatting arguments.
+            MultiSpan::from_spans(self.arg_spans.clone())
+        } else {
+            MultiSpan::from_span(self.fmtsp)
+        };
+        let refs =
+            self.invalid_refs.iter().map(|(r, pos)| (r.to_string(), self.arg_spans.get(*pos)));
+
+        let mut zero_based_note = false;
+
+        let count = self.pieces.len()
+            + self.arg_with_formatting.iter().filter(|fmt| fmt.precision_span.is_some()).count();
+        if self.names.is_empty() && !numbered_position_args && count != self.args.len() {
+            e = self.ecx.struct_span_err(
+                sp,
+                &format!(
+                    "{} positional argument{} in format string, but {}",
+                    count,
+                    pluralize!(count),
+                    self.describe_num_args(),
+                ),
+            );
+            for arg in &self.args {
+                // Point at the arguments that will be formatted.
+                e.span_label(arg.span, "");
+            }
+        } else {
+            let (mut refs, spans): (Vec<_>, Vec<_>) = refs.unzip();
+            // Avoid `invalid reference to positional arguments 7 and 7 (there is 1 argument)`
+            // for `println!("{7:7$}", 1);`
+            refs.sort();
+            refs.dedup();
+            let spans: Vec<_> = spans.into_iter().filter_map(|sp| sp.copied()).collect();
+            let sp = if self.arg_spans.is_empty() || spans.is_empty() {
+                MultiSpan::from_span(self.fmtsp)
+            } else {
+                MultiSpan::from_spans(spans)
+            };
+            let arg_list = if refs.len() == 1 {
+                format!("argument {}", refs[0])
+            } else {
+                let reg = refs.pop().unwrap();
+                format!("arguments {head} and {tail}", head = refs.join(", "), tail = reg)
+            };
+
+            e = self.ecx.struct_span_err(
+                sp,
+                &format!(
+                    "invalid reference to positional {} ({})",
+                    arg_list,
+                    self.describe_num_args()
+                ),
+            );
+            zero_based_note = true;
+        };
+
+        for fmt in &self.arg_with_formatting {
+            if let Some(span) = fmt.precision_span {
+                let span = self.fmtsp.from_inner(span);
+                match fmt.precision {
+                    parse::CountIsParam(pos) if pos > self.args.len() => {
+                        e.span_label(
+                            span,
+                            &format!(
+                                "this precision flag expects an `usize` argument at position {}, \
+                             but {}",
+                                pos,
+                                self.describe_num_args(),
+                            ),
+                        );
+                        zero_based_note = true;
+                    }
+                    parse::CountIsParam(pos) => {
+                        let count = self.pieces.len()
+                            + self
+                                .arg_with_formatting
+                                .iter()
+                                .filter(|fmt| fmt.precision_span.is_some())
+                                .count();
+                        e.span_label(span, &format!(
+                            "this precision flag adds an extra required argument at position {}, \
+                             which is why there {} expected",
+                            pos,
+                            if count == 1 {
+                                "is 1 argument".to_string()
+                            } else {
+                                format!("are {} arguments", count)
+                            },
+                        ));
+                        if let Some(arg) = self.args.get(pos) {
+                            e.span_label(
+                                arg.span,
+                                "this parameter corresponds to the precision flag",
+                            );
+                        }
+                        zero_based_note = true;
+                    }
+                    _ => {}
+                }
+            }
+            if let Some(span) = fmt.width_span {
+                let span = self.fmtsp.from_inner(span);
+                match fmt.width {
+                    parse::CountIsParam(pos) if pos > self.args.len() => {
+                        e.span_label(
+                            span,
+                            &format!(
+                                "this width flag expects an `usize` argument at position {}, \
+                             but {}",
+                                pos,
+                                self.describe_num_args(),
+                            ),
+                        );
+                        zero_based_note = true;
+                    }
+                    _ => {}
+                }
+            }
+        }
+        if zero_based_note {
+            e.note("positional arguments are zero-based");
+        }
+        if !self.arg_with_formatting.is_empty() {
+            e.note(
+                "for information about formatting flags, visit \
+                    https://doc.rust-lang.org/std/fmt/index.html",
+            );
+        }
+
+        e.emit();
+    }
+
+    /// Actually verifies and tracks a given format placeholder
+    /// (a.k.a. argument).
+    fn verify_arg_type(&mut self, arg: Position, ty: ArgumentType) {
+        match arg {
+            Exact(arg) => {
+                if self.args.len() <= arg {
+                    self.invalid_refs.push((arg, self.curpiece));
+                    return;
+                }
+                match ty {
+                    Placeholder(_) => {
+                        // record every (position, type) combination only once
+                        let seen_ty = &mut self.arg_unique_types[arg];
+                        let i = seen_ty.iter().position(|x| *x == ty).unwrap_or_else(|| {
+                            let i = seen_ty.len();
+                            seen_ty.push(ty);
+                            i
+                        });
+                        self.arg_types[arg].push(i);
+                    }
+                    Count => {
+                        if let Entry::Vacant(e) = self.count_positions.entry(arg) {
+                            let i = self.count_positions_count;
+                            e.insert(i);
+                            self.count_args.push(Exact(arg));
+                            self.count_positions_count += 1;
+                        }
+                    }
+                }
+            }
+
+            Named(name) => {
+                match self.names.get(&name) {
+                    Some(&idx) => {
+                        // Treat as positional arg.
+                        self.verify_arg_type(Exact(idx), ty)
+                    }
+                    None => {
+                        let capture_feature_enabled = self
+                            .ecx
+                            .ecfg
+                            .features
+                            .map_or(false, |features| features.format_args_capture);
+
+                        // For the moment capturing variables from format strings expanded from macros is
+                        // disabled (see RFC #2795)
+                        let can_capture = capture_feature_enabled && self.is_literal;
+
+                        if can_capture {
+                            // Treat this name as a variable to capture from the surrounding scope
+                            let idx = self.args.len();
+                            self.arg_types.push(Vec::new());
+                            self.arg_unique_types.push(Vec::new());
+                            self.args.push(
+                                self.ecx.expr_ident(self.fmtsp, Ident::new(name, self.fmtsp)),
+                            );
+                            self.names.insert(name, idx);
+                            self.verify_arg_type(Exact(idx), ty)
+                        } else {
+                            let msg = format!("there is no argument named `{}`", name);
+                            let sp = if self.is_literal {
+                                *self.arg_spans.get(self.curpiece).unwrap_or(&self.fmtsp)
+                            } else {
+                                self.fmtsp
+                            };
+                            let mut err = self.ecx.struct_span_err(sp, &msg[..]);
+
+                            if capture_feature_enabled && !self.is_literal {
+                                err.note(&format!(
+                                    "did you intend to capture a variable `{}` from \
+                                     the surrounding scope?",
+                                    name
+                                ));
+                                err.note(
+                                    "to avoid ambiguity, `format_args!` cannot capture variables \
+                                     when the format string is expanded from a macro",
+                                );
+                            } else if self.ecx.parse_sess().unstable_features.is_nightly_build() {
+                                err.help(&format!(
+                                    "if you intended to capture `{}` from the surrounding scope, add \
+                                     `#![feature(format_args_capture)]` to the crate attributes",
+                                    name
+                                ));
+                            }
+
+                            err.emit();
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    /// Builds the mapping between format placeholders and argument objects.
+    fn build_index_map(&mut self) {
+        // NOTE: Keep the ordering the same as `into_expr`'s expansion would do!
+        let args_len = self.args.len();
+        self.arg_index_map.reserve(args_len);
+
+        let mut sofar = 0usize;
+
+        // Map the arguments
+        for i in 0..args_len {
+            let arg_types = &self.arg_types[i];
+            let arg_offsets = arg_types.iter().map(|offset| sofar + *offset).collect::<Vec<_>>();
+            self.arg_index_map.push(arg_offsets);
+            sofar += self.arg_unique_types[i].len();
+        }
+
+        // Record starting index for counts, which appear just after arguments
+        self.count_args_index_offset = sofar;
+    }
+
+    fn rtpath(ecx: &ExtCtxt<'_>, s: Symbol) -> Vec<Ident> {
+        ecx.std_path(&[sym::fmt, sym::rt, sym::v1, s])
+    }
+
+    fn build_count(&self, c: parse::Count) -> P<ast::Expr> {
+        let sp = self.macsp;
+        let count = |c, arg| {
+            let mut path = Context::rtpath(self.ecx, sym::Count);
+            path.push(Ident::new(c, sp));
+            match arg {
+                Some(arg) => self.ecx.expr_call_global(sp, path, vec![arg]),
+                None => self.ecx.expr_path(self.ecx.path_global(sp, path)),
+            }
+        };
+        match c {
+            parse::CountIs(i) => count(sym::Is, Some(self.ecx.expr_usize(sp, i))),
+            parse::CountIsParam(i) => {
+                // This needs mapping too, as `i` is referring to a macro
+                // argument. If `i` is not found in `count_positions` then
+                // the error had already been emitted elsewhere.
+                let i = self.count_positions.get(&i).cloned().unwrap_or(0)
+                    + self.count_args_index_offset;
+                count(sym::Param, Some(self.ecx.expr_usize(sp, i)))
+            }
+            parse::CountImplied => count(sym::Implied, None),
+            // should never be the case, names are already resolved
+            parse::CountIsName(_) => panic!("should never happen"),
+        }
+    }
+
+    /// Build a literal expression from the accumulated string literals
+    fn build_literal_string(&mut self) -> P<ast::Expr> {
+        let sp = self.fmtsp;
+        let s = Symbol::intern(&self.literal);
+        self.literal.clear();
+        self.ecx.expr_str(sp, s)
+    }
+
+    /// Builds a static `rt::Argument` from a `parse::Piece` or append
+    /// to the `literal` string.
+    fn build_piece(
+        &mut self,
+        piece: &parse::Piece<'a>,
+        arg_index_consumed: &mut Vec<usize>,
+    ) -> Option<P<ast::Expr>> {
+        let sp = self.macsp;
+        match *piece {
+            parse::String(s) => {
+                self.literal.push_str(s);
+                None
+            }
+            parse::NextArgument(ref arg) => {
+                // Build the position
+                let pos = {
+                    match arg.position {
+                        parse::ArgumentIs(i) | parse::ArgumentImplicitlyIs(i) => {
+                            // Map to index in final generated argument array
+                            // in case of multiple types specified
+                            let arg_idx = match arg_index_consumed.get_mut(i) {
+                                None => 0, // error already emitted elsewhere
+                                Some(offset) => {
+                                    let idx_map = &self.arg_index_map[i];
+                                    // unwrap_or branch: error already emitted elsewhere
+                                    let arg_idx = *idx_map.get(*offset).unwrap_or(&0);
+                                    *offset += 1;
+                                    arg_idx
+                                }
+                            };
+                            self.ecx.expr_usize(sp, arg_idx)
+                        }
+
+                        // should never be the case, because names are already
+                        // resolved.
+                        parse::ArgumentNamed(_) => panic!("should never happen"),
+                    }
+                };
+
+                let simple_arg = parse::Argument {
+                    position: {
+                        // We don't have ArgumentNext any more, so we have to
+                        // track the current argument ourselves.
+                        let i = self.curarg;
+                        self.curarg += 1;
+                        parse::ArgumentIs(i)
+                    },
+                    format: parse::FormatSpec {
+                        fill: arg.format.fill,
+                        align: parse::AlignUnknown,
+                        flags: 0,
+                        precision: parse::CountImplied,
+                        precision_span: None,
+                        width: parse::CountImplied,
+                        width_span: None,
+                        ty: arg.format.ty,
+                        ty_span: arg.format.ty_span,
+                    },
+                };
+
+                let fill = arg.format.fill.unwrap_or(' ');
+
+                let pos_simple = arg.position.index() == simple_arg.position.index();
+
+                if arg.format.precision_span.is_some() || arg.format.width_span.is_some() {
+                    self.arg_with_formatting.push(arg.format);
+                }
+                if !pos_simple || arg.format != simple_arg.format || fill != ' ' {
+                    self.all_pieces_simple = false;
+                }
+
+                // Build the format
+                let fill = self.ecx.expr_lit(sp, ast::LitKind::Char(fill));
+                let align = |name| {
+                    let mut p = Context::rtpath(self.ecx, sym::Alignment);
+                    p.push(Ident::new(name, sp));
+                    self.ecx.path_global(sp, p)
+                };
+                let align = match arg.format.align {
+                    parse::AlignLeft => align(sym::Left),
+                    parse::AlignRight => align(sym::Right),
+                    parse::AlignCenter => align(sym::Center),
+                    parse::AlignUnknown => align(sym::Unknown),
+                };
+                let align = self.ecx.expr_path(align);
+                let flags = self.ecx.expr_u32(sp, arg.format.flags);
+                let prec = self.build_count(arg.format.precision);
+                let width = self.build_count(arg.format.width);
+                let path = self.ecx.path_global(sp, Context::rtpath(self.ecx, sym::FormatSpec));
+                let fmt = self.ecx.expr_struct(
+                    sp,
+                    path,
+                    vec![
+                        self.ecx.field_imm(sp, Ident::new(sym::fill, sp), fill),
+                        self.ecx.field_imm(sp, Ident::new(sym::align, sp), align),
+                        self.ecx.field_imm(sp, Ident::new(sym::flags, sp), flags),
+                        self.ecx.field_imm(sp, Ident::new(sym::precision, sp), prec),
+                        self.ecx.field_imm(sp, Ident::new(sym::width, sp), width),
+                    ],
+                );
+
+                let path = self.ecx.path_global(sp, Context::rtpath(self.ecx, sym::Argument));
+                Some(self.ecx.expr_struct(
+                    sp,
+                    path,
+                    vec![
+                        self.ecx.field_imm(sp, Ident::new(sym::position, sp), pos),
+                        self.ecx.field_imm(sp, Ident::new(sym::format, sp), fmt),
+                    ],
+                ))
+            }
+        }
+    }
+
+    /// Actually builds the expression which the format_args! block will be
+    /// expanded to.
+    fn into_expr(self) -> P<ast::Expr> {
+        let mut locals =
+            Vec::with_capacity((0..self.args.len()).map(|i| self.arg_unique_types[i].len()).sum());
+        let mut counts = Vec::with_capacity(self.count_args.len());
+        let mut pats = Vec::with_capacity(self.args.len());
+        let mut heads = Vec::with_capacity(self.args.len());
+
+        let names_pos: Vec<_> = (0..self.args.len())
+            .map(|i| Ident::from_str_and_span(&format!("arg{}", i), self.macsp))
+            .collect();
+
+        // First, build up the static array which will become our precompiled
+        // format "string"
+        let pieces = self.ecx.expr_vec_slice(self.fmtsp, self.str_pieces);
+
+        // Before consuming the expressions, we have to remember spans for
+        // count arguments as they are now generated separate from other
+        // arguments, hence have no access to the `P<ast::Expr>`'s.
+        let spans_pos: Vec<_> = self.args.iter().map(|e| e.span).collect();
+
+        // Right now there is a bug such that for the expression:
+        //      foo(bar(&1))
+        // the lifetime of `1` doesn't outlast the call to `bar`, so it's not
+        // valid for the call to `foo`. To work around this all arguments to the
+        // format! string are shoved into locals. Furthermore, we shove the address
+        // of each variable because we don't want to move out of the arguments
+        // passed to this function.
+        for (i, e) in self.args.into_iter().enumerate() {
+            let name = names_pos[i];
+            let span = self.ecx.with_def_site_ctxt(e.span);
+            pats.push(self.ecx.pat_ident(span, name));
+            for arg_ty in self.arg_unique_types[i].iter() {
+                locals.push(Context::format_arg(self.ecx, self.macsp, e.span, arg_ty, name));
+            }
+            heads.push(self.ecx.expr_addr_of(e.span, e));
+        }
+        for pos in self.count_args {
+            let index = match pos {
+                Exact(i) => i,
+                _ => panic!("should never happen"),
+            };
+            let name = names_pos[index];
+            let span = spans_pos[index];
+            counts.push(Context::format_arg(self.ecx, self.macsp, span, &Count, name));
+        }
+
+        // Now create a vector containing all the arguments
+        let args = locals.into_iter().chain(counts.into_iter());
+
+        let args_array = self.ecx.expr_vec(self.macsp, args.collect());
+
+        // Constructs an AST equivalent to:
+        //
+        //      match (&arg0, &arg1) {
+        //          (tmp0, tmp1) => args_array
+        //      }
+        //
+        // It was:
+        //
+        //      let tmp0 = &arg0;
+        //      let tmp1 = &arg1;
+        //      args_array
+        //
+        // Because of #11585 the new temporary lifetime rule, the enclosing
+        // statements for these temporaries become the let's themselves.
+        // If one or more of them are RefCell's, RefCell borrow() will also
+        // end there; they don't last long enough for args_array to use them.
+        // The match expression solves the scope problem.
+        //
+        // Note, it may also very well be transformed to:
+        //
+        //      match arg0 {
+        //          ref tmp0 => {
+        //              match arg1 => {
+        //                  ref tmp1 => args_array } } }
+        //
+        // But the nested match expression is proved to perform not as well
+        // as series of let's; the first approach does.
+        let pat = self.ecx.pat_tuple(self.macsp, pats);
+        let arm = self.ecx.arm(self.macsp, pat, args_array);
+        let head = self.ecx.expr(self.macsp, ast::ExprKind::Tup(heads));
+        let result = self.ecx.expr_match(self.macsp, head, vec![arm]);
+
+        let args_slice = self.ecx.expr_addr_of(self.macsp, result);
+
+        // Now create the fmt::Arguments struct with all our locals we created.
+        let (fn_name, fn_args) = if self.all_pieces_simple {
+            ("new_v1", vec![pieces, args_slice])
+        } else {
+            // Build up the static array which will store our precompiled
+            // nonstandard placeholders, if there are any.
+            let fmt = self.ecx.expr_vec_slice(self.macsp, self.pieces);
+
+            ("new_v1_formatted", vec![pieces, args_slice, fmt])
+        };
+
+        let path = self.ecx.std_path(&[sym::fmt, sym::Arguments, Symbol::intern(fn_name)]);
+        self.ecx.expr_call_global(self.macsp, path, fn_args)
+    }
+
+    fn format_arg(
+        ecx: &ExtCtxt<'_>,
+        macsp: Span,
+        mut sp: Span,
+        ty: &ArgumentType,
+        arg: Ident,
+    ) -> P<ast::Expr> {
+        sp = ecx.with_def_site_ctxt(sp);
+        let arg = ecx.expr_ident(sp, arg);
+        let trait_ = match *ty {
+            Placeholder(trait_) if trait_ == "<invalid>" => return DummyResult::raw_expr(sp, true),
+            Placeholder(trait_) => trait_,
+            Count => {
+                let path = ecx.std_path(&[sym::fmt, sym::ArgumentV1, sym::from_usize]);
+                return ecx.expr_call_global(macsp, path, vec![arg]);
+            }
+        };
+
+        let path = ecx.std_path(&[sym::fmt, Symbol::intern(trait_), sym::fmt]);
+        let format_fn = ecx.path_global(sp, path);
+        let path = ecx.std_path(&[sym::fmt, sym::ArgumentV1, sym::new]);
+        ecx.expr_call_global(macsp, path, vec![arg, ecx.expr_path(format_fn)])
+    }
+}
+
+fn expand_format_args_impl<'cx>(
+    ecx: &'cx mut ExtCtxt<'_>,
+    mut sp: Span,
+    tts: TokenStream,
+    nl: bool,
+) -> Box<dyn base::MacResult + 'cx> {
+    sp = ecx.with_def_site_ctxt(sp);
+    match parse_args(ecx, sp, tts) {
+        Ok((efmt, args, names)) => {
+            MacEager::expr(expand_preparsed_format_args(ecx, sp, efmt, args, names, nl))
+        }
+        Err(mut err) => {
+            err.emit();
+            DummyResult::any(sp)
+        }
+    }
+}
+
+pub fn expand_format_args<'cx>(
+    ecx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    expand_format_args_impl(ecx, sp, tts, false)
+}
+
+pub fn expand_format_args_nl<'cx>(
+    ecx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    expand_format_args_impl(ecx, sp, tts, true)
+}
+
+/// Take the various parts of `format_args!(efmt, args..., name=names...)`
+/// and construct the appropriate formatting expression.
+pub fn expand_preparsed_format_args(
+    ecx: &mut ExtCtxt<'_>,
+    sp: Span,
+    efmt: P<ast::Expr>,
+    args: Vec<P<ast::Expr>>,
+    names: FxHashMap<Symbol, usize>,
+    append_newline: bool,
+) -> P<ast::Expr> {
+    // NOTE: this verbose way of initializing `Vec<Vec<ArgumentType>>` is because
+    // `ArgumentType` does not derive `Clone`.
+    let arg_types: Vec<_> = (0..args.len()).map(|_| Vec::new()).collect();
+    let arg_unique_types: Vec<_> = (0..args.len()).map(|_| Vec::new()).collect();
+
+    let mut macsp = ecx.call_site();
+    macsp = ecx.with_def_site_ctxt(macsp);
+
+    let msg = "format argument must be a string literal";
+    let fmt_sp = efmt.span;
+    let (fmt_str, fmt_style, fmt_span) = match expr_to_spanned_string(ecx, efmt, msg) {
+        Ok(mut fmt) if append_newline => {
+            fmt.0 = Symbol::intern(&format!("{}\n", fmt.0));
+            fmt
+        }
+        Ok(fmt) => fmt,
+        Err(err) => {
+            if let Some(mut err) = err {
+                let sugg_fmt = match args.len() {
+                    0 => "{}".to_string(),
+                    _ => format!("{}{{}}", "{} ".repeat(args.len())),
+                };
+                err.span_suggestion(
+                    fmt_sp.shrink_to_lo(),
+                    "you might be missing a string literal to format with",
+                    format!("\"{}\", ", sugg_fmt),
+                    Applicability::MaybeIncorrect,
+                );
+                err.emit();
+            }
+            return DummyResult::raw_expr(sp, true);
+        }
+    };
+
+    let str_style = match fmt_style {
+        ast::StrStyle::Cooked => None,
+        ast::StrStyle::Raw(raw) => Some(raw as usize),
+    };
+
+    let fmt_str = &fmt_str.as_str(); // for the suggestions below
+    let fmt_snippet = ecx.source_map().span_to_snippet(fmt_sp).ok();
+    let mut parser = parse::Parser::new(
+        fmt_str,
+        str_style,
+        fmt_snippet,
+        append_newline,
+        parse::ParseMode::Format,
+    );
+
+    let mut unverified_pieces = Vec::new();
+    while let Some(piece) = parser.next() {
+        if !parser.errors.is_empty() {
+            break;
+        } else {
+            unverified_pieces.push(piece);
+        }
+    }
+
+    if !parser.errors.is_empty() {
+        let err = parser.errors.remove(0);
+        let sp = fmt_span.from_inner(err.span);
+        let mut e = ecx.struct_span_err(sp, &format!("invalid format string: {}", err.description));
+        e.span_label(sp, err.label + " in format string");
+        if let Some(note) = err.note {
+            e.note(&note);
+        }
+        if let Some((label, span)) = err.secondary_label {
+            let sp = fmt_span.from_inner(span);
+            e.span_label(sp, label);
+        }
+        e.emit();
+        return DummyResult::raw_expr(sp, true);
+    }
+
+    let arg_spans = parser.arg_places.iter().map(|span| fmt_span.from_inner(*span)).collect();
+
+    let named_pos: FxHashSet<usize> = names.values().cloned().collect();
+
+    let mut cx = Context {
+        ecx,
+        args,
+        arg_types,
+        arg_unique_types,
+        names,
+        curarg: 0,
+        curpiece: 0,
+        arg_index_map: Vec::new(),
+        count_args: Vec::new(),
+        count_positions: FxHashMap::default(),
+        count_positions_count: 0,
+        count_args_index_offset: 0,
+        literal: String::new(),
+        pieces: Vec::with_capacity(unverified_pieces.len()),
+        str_pieces: Vec::with_capacity(unverified_pieces.len()),
+        all_pieces_simple: true,
+        macsp,
+        fmtsp: fmt_span,
+        invalid_refs: Vec::new(),
+        arg_spans,
+        arg_with_formatting: Vec::new(),
+        is_literal: parser.is_literal,
+    };
+
+    // This needs to happen *after* the Parser has consumed all pieces to create all the spans
+    let pieces = unverified_pieces
+        .into_iter()
+        .map(|mut piece| {
+            cx.verify_piece(&piece);
+            cx.resolve_name_inplace(&mut piece);
+            piece
+        })
+        .collect::<Vec<_>>();
+
+    let numbered_position_args = pieces.iter().any(|arg: &parse::Piece<'_>| match *arg {
+        parse::String(_) => false,
+        parse::NextArgument(arg) => match arg.position {
+            parse::Position::ArgumentIs(_) => true,
+            _ => false,
+        },
+    });
+
+    cx.build_index_map();
+
+    let mut arg_index_consumed = vec![0usize; cx.arg_index_map.len()];
+
+    for piece in pieces {
+        if let Some(piece) = cx.build_piece(&piece, &mut arg_index_consumed) {
+            let s = cx.build_literal_string();
+            cx.str_pieces.push(s);
+            cx.pieces.push(piece);
+        }
+    }
+
+    if !cx.literal.is_empty() {
+        let s = cx.build_literal_string();
+        cx.str_pieces.push(s);
+    }
+
+    if !cx.invalid_refs.is_empty() {
+        cx.report_invalid_references(numbered_position_args);
+    }
+
+    // Make sure that all arguments were used and all arguments have types.
+    let errs = cx
+        .arg_types
+        .iter()
+        .enumerate()
+        .filter(|(i, ty)| ty.is_empty() && !cx.count_positions.contains_key(&i))
+        .map(|(i, _)| {
+            let msg = if named_pos.contains(&i) {
+                // named argument
+                "named argument never used"
+            } else {
+                // positional argument
+                "argument never used"
+            };
+            (cx.args[i].span, msg)
+        })
+        .collect::<Vec<_>>();
+
+    let errs_len = errs.len();
+    if !errs.is_empty() {
+        let args_used = cx.arg_types.len() - errs_len;
+        let args_unused = errs_len;
+
+        let mut diag = {
+            if let [(sp, msg)] = &errs[..] {
+                let mut diag = cx.ecx.struct_span_err(*sp, *msg);
+                diag.span_label(*sp, *msg);
+                diag
+            } else {
+                let mut diag = cx.ecx.struct_span_err(
+                    errs.iter().map(|&(sp, _)| sp).collect::<Vec<Span>>(),
+                    "multiple unused formatting arguments",
+                );
+                diag.span_label(cx.fmtsp, "multiple missing formatting specifiers");
+                for (sp, msg) in errs {
+                    diag.span_label(sp, msg);
+                }
+                diag
+            }
+        };
+
+        // Used to ensure we only report translations for *one* kind of foreign format.
+        let mut found_foreign = false;
+        // Decide if we want to look for foreign formatting directives.
+        if args_used < args_unused {
+            use super::format_foreign as foreign;
+
+            // The set of foreign substitutions we've explained.  This prevents spamming the user
+            // with `%d should be written as {}` over and over again.
+            let mut explained = FxHashSet::default();
+
+            macro_rules! check_foreign {
+                ($kind:ident) => {{
+                    let mut show_doc_note = false;
+
+                    let mut suggestions = vec![];
+                    // account for `"` and account for raw strings `r#`
+                    let padding = str_style.map(|i| i + 2).unwrap_or(1);
+                    for sub in foreign::$kind::iter_subs(fmt_str, padding) {
+                        let trn = match sub.translate() {
+                            Some(trn) => trn,
+
+                            // If it has no translation, don't call it out specifically.
+                            None => continue,
+                        };
+
+                        let pos = sub.position();
+                        let sub = String::from(sub.as_str());
+                        if explained.contains(&sub) {
+                            continue;
+                        }
+                        explained.insert(sub.clone());
+
+                        if !found_foreign {
+                            found_foreign = true;
+                            show_doc_note = true;
+                        }
+
+                        if let Some(inner_sp) = pos {
+                            let sp = fmt_sp.from_inner(inner_sp);
+                            suggestions.push((sp, trn));
+                        } else {
+                            diag.help(&format!("`{}` should be written as `{}`", sub, trn));
+                        }
+                    }
+
+                    if show_doc_note {
+                        diag.note(concat!(
+                            stringify!($kind),
+                            " formatting not supported; see the documentation for `std::fmt`",
+                        ));
+                    }
+                    if suggestions.len() > 0 {
+                        diag.multipart_suggestion(
+                            "format specifiers use curly braces",
+                            suggestions,
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                }};
+            }
+
+            check_foreign!(printf);
+            if !found_foreign {
+                check_foreign!(shell);
+            }
+        }
+        if !found_foreign && errs_len == 1 {
+            diag.span_label(cx.fmtsp, "formatting specifier missing");
+        }
+
+        diag.emit();
+    }
+
+    cx.into_expr()
+}
diff --git a/compiler/rustc_builtin_macros/src/format_foreign.rs b/compiler/rustc_builtin_macros/src/format_foreign.rs
new file mode 100644
index 00000000000..85cf4c42e94
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/format_foreign.rs
@@ -0,0 +1,823 @@
+pub mod printf {
+    use super::strcursor::StrCursor as Cur;
+    use rustc_span::InnerSpan;
+
+    /// Represents a single `printf`-style substitution.
+    #[derive(Clone, PartialEq, Debug)]
+    pub enum Substitution<'a> {
+        /// A formatted output substitution with its internal byte offset.
+        Format(Format<'a>),
+        /// A literal `%%` escape.
+        Escape,
+    }
+
+    impl<'a> Substitution<'a> {
+        pub fn as_str(&self) -> &str {
+            match *self {
+                Substitution::Format(ref fmt) => fmt.span,
+                Substitution::Escape => "%%",
+            }
+        }
+
+        pub fn position(&self) -> Option<InnerSpan> {
+            match *self {
+                Substitution::Format(ref fmt) => Some(fmt.position),
+                _ => None,
+            }
+        }
+
+        pub fn set_position(&mut self, start: usize, end: usize) {
+            if let Substitution::Format(ref mut fmt) = self {
+                fmt.position = InnerSpan::new(start, end);
+            }
+        }
+
+        /// Translate this substitution into an equivalent Rust formatting directive.
+        ///
+        /// This ignores cases where the substitution does not have an exact equivalent, or where
+        /// the substitution would be unnecessary.
+        pub fn translate(&self) -> Option<String> {
+            match *self {
+                Substitution::Format(ref fmt) => fmt.translate(),
+                Substitution::Escape => None,
+            }
+        }
+    }
+
+    #[derive(Clone, PartialEq, Debug)]
+    /// A single `printf`-style formatting directive.
+    pub struct Format<'a> {
+        /// The entire original formatting directive.
+        pub span: &'a str,
+        /// The (1-based) parameter to be converted.
+        pub parameter: Option<u16>,
+        /// Formatting flags.
+        pub flags: &'a str,
+        /// Minimum width of the output.
+        pub width: Option<Num>,
+        /// Precision of the conversion.
+        pub precision: Option<Num>,
+        /// Length modifier for the conversion.
+        pub length: Option<&'a str>,
+        /// Type of parameter being converted.
+        pub type_: &'a str,
+        /// Byte offset for the start and end of this formatting directive.
+        pub position: InnerSpan,
+    }
+
+    impl Format<'_> {
+        /// Translate this directive into an equivalent Rust formatting directive.
+        ///
+        /// Returns `None` in cases where the `printf` directive does not have an exact Rust
+        /// equivalent, rather than guessing.
+        pub fn translate(&self) -> Option<String> {
+            use std::fmt::Write;
+
+            let (c_alt, c_zero, c_left, c_plus) = {
+                let mut c_alt = false;
+                let mut c_zero = false;
+                let mut c_left = false;
+                let mut c_plus = false;
+                for c in self.flags.chars() {
+                    match c {
+                        '#' => c_alt = true,
+                        '0' => c_zero = true,
+                        '-' => c_left = true,
+                        '+' => c_plus = true,
+                        _ => return None,
+                    }
+                }
+                (c_alt, c_zero, c_left, c_plus)
+            };
+
+            // Has a special form in Rust for numbers.
+            let fill = c_zero.then_some("0");
+
+            let align = c_left.then_some("<");
+
+            // Rust doesn't have an equivalent to the `' '` flag.
+            let sign = c_plus.then_some("+");
+
+            // Not *quite* the same, depending on the type...
+            let alt = c_alt;
+
+            let width = match self.width {
+                Some(Num::Next) => {
+                    // NOTE: Rust doesn't support this.
+                    return None;
+                }
+                w @ Some(Num::Arg(_)) => w,
+                w @ Some(Num::Num(_)) => w,
+                None => None,
+            };
+
+            let precision = self.precision;
+
+            // NOTE: although length *can* have an effect, we can't duplicate the effect in Rust, so
+            // we just ignore it.
+
+            let (type_, use_zero_fill, is_int) = match self.type_ {
+                "d" | "i" | "u" => (None, true, true),
+                "f" | "F" => (None, false, false),
+                "s" | "c" => (None, false, false),
+                "e" | "E" => (Some(self.type_), true, false),
+                "x" | "X" | "o" => (Some(self.type_), true, true),
+                "p" => (Some(self.type_), false, true),
+                "g" => (Some("e"), true, false),
+                "G" => (Some("E"), true, false),
+                _ => return None,
+            };
+
+            let (fill, width, precision) = match (is_int, width, precision) {
+                (true, Some(_), Some(_)) => {
+                    // Rust can't duplicate this insanity.
+                    return None;
+                }
+                (true, None, Some(p)) => (Some("0"), Some(p), None),
+                (true, w, None) => (fill, w, None),
+                (false, w, p) => (fill, w, p),
+            };
+
+            let align = match (self.type_, width.is_some(), align.is_some()) {
+                ("s", true, false) => Some(">"),
+                _ => align,
+            };
+
+            let (fill, zero_fill) = match (fill, use_zero_fill) {
+                (Some("0"), true) => (None, true),
+                (fill, _) => (fill, false),
+            };
+
+            let alt = match type_ {
+                Some("x" | "X") => alt,
+                _ => false,
+            };
+
+            let has_options = fill.is_some()
+                || align.is_some()
+                || sign.is_some()
+                || alt
+                || zero_fill
+                || width.is_some()
+                || precision.is_some()
+                || type_.is_some();
+
+            // Initialise with a rough guess.
+            let cap = self.span.len() + if has_options { 2 } else { 0 };
+            let mut s = String::with_capacity(cap);
+
+            s.push_str("{");
+
+            if let Some(arg) = self.parameter {
+                write!(s, "{}", arg.checked_sub(1)?).ok()?;
+            }
+
+            if has_options {
+                s.push_str(":");
+
+                let align = if let Some(fill) = fill {
+                    s.push_str(fill);
+                    align.or(Some(">"))
+                } else {
+                    align
+                };
+
+                if let Some(align) = align {
+                    s.push_str(align);
+                }
+
+                if let Some(sign) = sign {
+                    s.push_str(sign);
+                }
+
+                if alt {
+                    s.push_str("#");
+                }
+
+                if zero_fill {
+                    s.push_str("0");
+                }
+
+                if let Some(width) = width {
+                    width.translate(&mut s).ok()?;
+                }
+
+                if let Some(precision) = precision {
+                    s.push_str(".");
+                    precision.translate(&mut s).ok()?;
+                }
+
+                if let Some(type_) = type_ {
+                    s.push_str(type_);
+                }
+            }
+
+            s.push_str("}");
+            Some(s)
+        }
+    }
+
+    /// A general number used in a `printf` formatting directive.
+    #[derive(Copy, Clone, PartialEq, Debug)]
+    pub enum Num {
+        // The range of these values is technically bounded by `NL_ARGMAX`... but, at least for GNU
+        // libc, it apparently has no real fixed limit.  A `u16` is used here on the basis that it
+        // is *vanishingly* unlikely that *anyone* is going to try formatting something wider, or
+        // with more precision, than 32 thousand positions which is so wide it couldn't possibly fit
+        // on a screen.
+        /// A specific, fixed value.
+        Num(u16),
+        /// The value is derived from a positional argument.
+        Arg(u16),
+        /// The value is derived from the "next" unconverted argument.
+        Next,
+    }
+
+    impl Num {
+        fn from_str(s: &str, arg: Option<&str>) -> Self {
+            if let Some(arg) = arg {
+                Num::Arg(arg.parse().unwrap_or_else(|_| panic!("invalid format arg `{:?}`", arg)))
+            } else if s == "*" {
+                Num::Next
+            } else {
+                Num::Num(s.parse().unwrap_or_else(|_| panic!("invalid format num `{:?}`", s)))
+            }
+        }
+
+        fn translate(&self, s: &mut String) -> std::fmt::Result {
+            use std::fmt::Write;
+            match *self {
+                Num::Num(n) => write!(s, "{}", n),
+                Num::Arg(n) => {
+                    let n = n.checked_sub(1).ok_or(std::fmt::Error)?;
+                    write!(s, "{}$", n)
+                }
+                Num::Next => write!(s, "*"),
+            }
+        }
+    }
+
+    /// Returns an iterator over all substitutions in a given string.
+    pub fn iter_subs(s: &str, start_pos: usize) -> Substitutions<'_> {
+        Substitutions { s, pos: start_pos }
+    }
+
+    /// Iterator over substitutions in a string.
+    pub struct Substitutions<'a> {
+        s: &'a str,
+        pos: usize,
+    }
+
+    impl<'a> Iterator for Substitutions<'a> {
+        type Item = Substitution<'a>;
+        fn next(&mut self) -> Option<Self::Item> {
+            let (mut sub, tail) = parse_next_substitution(self.s)?;
+            self.s = tail;
+            match sub {
+                Substitution::Format(_) => {
+                    if let Some(inner_span) = sub.position() {
+                        sub.set_position(inner_span.start + self.pos, inner_span.end + self.pos);
+                        self.pos += inner_span.end;
+                    }
+                }
+                Substitution::Escape => self.pos += 2,
+            }
+            Some(sub)
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            // Substitutions are at least 2 characters long.
+            (0, Some(self.s.len() / 2))
+        }
+    }
+
+    enum State {
+        Start,
+        Flags,
+        Width,
+        WidthArg,
+        Prec,
+        PrecInner,
+        Length,
+        Type,
+    }
+
+    /// Parse the next substitution from the input string.
+    pub fn parse_next_substitution(s: &str) -> Option<(Substitution<'_>, &str)> {
+        use self::State::*;
+
+        let at = {
+            let start = s.find('%')?;
+            if let '%' = s[start + 1..].chars().next()? {
+                return Some((Substitution::Escape, &s[start + 2..]));
+            }
+
+            Cur::new_at(&s[..], start)
+        };
+
+        // This is meant to be a translation of the following regex:
+        //
+        // ```regex
+        // (?x)
+        // ^ %
+        // (?: (?P<parameter> \d+) \$ )?
+        // (?P<flags> [-+ 0\#']* )
+        // (?P<width> \d+ | \* (?: (?P<widtha> \d+) \$ )? )?
+        // (?: \. (?P<precision> \d+ | \* (?: (?P<precisiona> \d+) \$ )? ) )?
+        // (?P<length>
+        //     # Standard
+        //     hh | h | ll | l | L | z | j | t
+        //
+        //     # Other
+        //     | I32 | I64 | I | q
+        // )?
+        // (?P<type> . )
+        // ```
+
+        // Used to establish the full span at the end.
+        let start = at;
+        // The current position within the string.
+        let mut at = at.at_next_cp()?;
+        // `c` is the next codepoint, `next` is a cursor after it.
+        let (mut c, mut next) = at.next_cp()?;
+
+        // Update `at`, `c`, and `next`, exiting if we're out of input.
+        macro_rules! move_to {
+            ($cur:expr) => {{
+                at = $cur;
+                let (c_, next_) = at.next_cp()?;
+                c = c_;
+                next = next_;
+            }};
+        }
+
+        // Constructs a result when parsing fails.
+        //
+        // Note: `move` used to capture copies of the cursors as they are *now*.
+        let fallback = move || {
+            Some((
+                Substitution::Format(Format {
+                    span: start.slice_between(next).unwrap(),
+                    parameter: None,
+                    flags: "",
+                    width: None,
+                    precision: None,
+                    length: None,
+                    type_: at.slice_between(next).unwrap(),
+                    position: InnerSpan::new(start.at, next.at),
+                }),
+                next.slice_after(),
+            ))
+        };
+
+        // Next parsing state.
+        let mut state = Start;
+
+        // Sadly, Rust isn't *quite* smart enough to know these *must* be initialised by the end.
+        let mut parameter: Option<u16> = None;
+        let mut flags: &str = "";
+        let mut width: Option<Num> = None;
+        let mut precision: Option<Num> = None;
+        let mut length: Option<&str> = None;
+        let mut type_: &str = "";
+        let end: Cur<'_>;
+
+        if let Start = state {
+            match c {
+                '1'..='9' => {
+                    let end = at_next_cp_while(next, is_digit);
+                    match end.next_cp() {
+                        // Yes, this *is* the parameter.
+                        Some(('$', end2)) => {
+                            state = Flags;
+                            parameter = Some(at.slice_between(end).unwrap().parse().unwrap());
+                            move_to!(end2);
+                        }
+                        // Wait, no, actually, it's the width.
+                        Some(_) => {
+                            state = Prec;
+                            parameter = None;
+                            flags = "";
+                            width = Some(Num::from_str(at.slice_between(end).unwrap(), None));
+                            move_to!(end);
+                        }
+                        // It's invalid, is what it is.
+                        None => return fallback(),
+                    }
+                }
+                _ => {
+                    state = Flags;
+                    parameter = None;
+                    move_to!(at);
+                }
+            }
+        }
+
+        if let Flags = state {
+            let end = at_next_cp_while(at, is_flag);
+            state = Width;
+            flags = at.slice_between(end).unwrap();
+            move_to!(end);
+        }
+
+        if let Width = state {
+            match c {
+                '*' => {
+                    state = WidthArg;
+                    move_to!(next);
+                }
+                '1'..='9' => {
+                    let end = at_next_cp_while(next, is_digit);
+                    state = Prec;
+                    width = Some(Num::from_str(at.slice_between(end).unwrap(), None));
+                    move_to!(end);
+                }
+                _ => {
+                    state = Prec;
+                    width = None;
+                    move_to!(at);
+                }
+            }
+        }
+
+        if let WidthArg = state {
+            let end = at_next_cp_while(at, is_digit);
+            match end.next_cp() {
+                Some(('$', end2)) => {
+                    state = Prec;
+                    width = Some(Num::from_str("", Some(at.slice_between(end).unwrap())));
+                    move_to!(end2);
+                }
+                _ => {
+                    state = Prec;
+                    width = Some(Num::Next);
+                    move_to!(end);
+                }
+            }
+        }
+
+        if let Prec = state {
+            match c {
+                '.' => {
+                    state = PrecInner;
+                    move_to!(next);
+                }
+                _ => {
+                    state = Length;
+                    precision = None;
+                    move_to!(at);
+                }
+            }
+        }
+
+        if let PrecInner = state {
+            match c {
+                '*' => {
+                    let end = at_next_cp_while(next, is_digit);
+                    match end.next_cp() {
+                        Some(('$', end2)) => {
+                            state = Length;
+                            precision = Some(Num::from_str("*", next.slice_between(end)));
+                            move_to!(end2);
+                        }
+                        _ => {
+                            state = Length;
+                            precision = Some(Num::Next);
+                            move_to!(end);
+                        }
+                    }
+                }
+                '0'..='9' => {
+                    let end = at_next_cp_while(next, is_digit);
+                    state = Length;
+                    precision = Some(Num::from_str(at.slice_between(end).unwrap(), None));
+                    move_to!(end);
+                }
+                _ => return fallback(),
+            }
+        }
+
+        if let Length = state {
+            let c1_next1 = next.next_cp();
+            match (c, c1_next1) {
+                ('h', Some(('h', next1))) | ('l', Some(('l', next1))) => {
+                    state = Type;
+                    length = Some(at.slice_between(next1).unwrap());
+                    move_to!(next1);
+                }
+
+                ('h' | 'l' | 'L' | 'z' | 'j' | 't' | 'q', _) => {
+                    state = Type;
+                    length = Some(at.slice_between(next).unwrap());
+                    move_to!(next);
+                }
+
+                ('I', _) => {
+                    let end = next
+                        .at_next_cp()
+                        .and_then(|end| end.at_next_cp())
+                        .map(|end| (next.slice_between(end).unwrap(), end));
+                    let end = match end {
+                        Some(("32", end)) => end,
+                        Some(("64", end)) => end,
+                        _ => next,
+                    };
+                    state = Type;
+                    length = Some(at.slice_between(end).unwrap());
+                    move_to!(end);
+                }
+
+                _ => {
+                    state = Type;
+                    length = None;
+                    move_to!(at);
+                }
+            }
+        }
+
+        if let Type = state {
+            drop(c);
+            type_ = at.slice_between(next).unwrap();
+
+            // Don't use `move_to!` here, as we *can* be at the end of the input.
+            at = next;
+        }
+
+        drop(c);
+        drop(next);
+
+        end = at;
+        let position = InnerSpan::new(start.at, end.at);
+
+        let f = Format {
+            span: start.slice_between(end).unwrap(),
+            parameter,
+            flags,
+            width,
+            precision,
+            length,
+            type_,
+            position,
+        };
+        Some((Substitution::Format(f), end.slice_after()))
+    }
+
+    fn at_next_cp_while<F>(mut cur: Cur<'_>, mut pred: F) -> Cur<'_>
+    where
+        F: FnMut(char) -> bool,
+    {
+        loop {
+            match cur.next_cp() {
+                Some((c, next)) => {
+                    if pred(c) {
+                        cur = next;
+                    } else {
+                        return cur;
+                    }
+                }
+                None => return cur,
+            }
+        }
+    }
+
+    fn is_digit(c: char) -> bool {
+        match c {
+            '0'..='9' => true,
+            _ => false,
+        }
+    }
+
+    fn is_flag(c: char) -> bool {
+        match c {
+            '0' | '-' | '+' | ' ' | '#' | '\'' => true,
+            _ => false,
+        }
+    }
+
+    #[cfg(test)]
+    mod tests;
+}
+
+pub mod shell {
+    use super::strcursor::StrCursor as Cur;
+    use rustc_span::InnerSpan;
+
+    #[derive(Clone, PartialEq, Debug)]
+    pub enum Substitution<'a> {
+        Ordinal(u8, (usize, usize)),
+        Name(&'a str, (usize, usize)),
+        Escape((usize, usize)),
+    }
+
+    impl Substitution<'_> {
+        pub fn as_str(&self) -> String {
+            match self {
+                Substitution::Ordinal(n, _) => format!("${}", n),
+                Substitution::Name(n, _) => format!("${}", n),
+                Substitution::Escape(_) => "$$".into(),
+            }
+        }
+
+        pub fn position(&self) -> Option<InnerSpan> {
+            match self {
+                Substitution::Ordinal(_, pos)
+                | Substitution::Name(_, pos)
+                | Substitution::Escape(pos) => Some(InnerSpan::new(pos.0, pos.1)),
+            }
+        }
+
+        pub fn set_position(&mut self, start: usize, end: usize) {
+            match self {
+                Substitution::Ordinal(_, ref mut pos)
+                | Substitution::Name(_, ref mut pos)
+                | Substitution::Escape(ref mut pos) => *pos = (start, end),
+            }
+        }
+
+        pub fn translate(&self) -> Option<String> {
+            match *self {
+                Substitution::Ordinal(n, _) => Some(format!("{{{}}}", n)),
+                Substitution::Name(n, _) => Some(format!("{{{}}}", n)),
+                Substitution::Escape(_) => None,
+            }
+        }
+    }
+
+    /// Returns an iterator over all substitutions in a given string.
+    pub fn iter_subs(s: &str, start_pos: usize) -> Substitutions<'_> {
+        Substitutions { s, pos: start_pos }
+    }
+
+    /// Iterator over substitutions in a string.
+    pub struct Substitutions<'a> {
+        s: &'a str,
+        pos: usize,
+    }
+
+    impl<'a> Iterator for Substitutions<'a> {
+        type Item = Substitution<'a>;
+        fn next(&mut self) -> Option<Self::Item> {
+            match parse_next_substitution(self.s) {
+                Some((mut sub, tail)) => {
+                    self.s = tail;
+                    if let Some(InnerSpan { start, end }) = sub.position() {
+                        sub.set_position(start + self.pos, end + self.pos);
+                        self.pos += end;
+                    }
+                    Some(sub)
+                }
+                None => None,
+            }
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            (0, Some(self.s.len()))
+        }
+    }
+
+    /// Parse the next substitution from the input string.
+    pub fn parse_next_substitution(s: &str) -> Option<(Substitution<'_>, &str)> {
+        let at = {
+            let start = s.find('$')?;
+            match s[start + 1..].chars().next()? {
+                '$' => return Some((Substitution::Escape((start, start + 2)), &s[start + 2..])),
+                c @ '0'..='9' => {
+                    let n = (c as u8) - b'0';
+                    return Some((Substitution::Ordinal(n, (start, start + 2)), &s[start + 2..]));
+                }
+                _ => { /* fall-through */ }
+            }
+
+            Cur::new_at(&s[..], start)
+        };
+
+        let at = at.at_next_cp()?;
+        let (c, inner) = at.next_cp()?;
+
+        if !is_ident_head(c) {
+            None
+        } else {
+            let end = at_next_cp_while(inner, is_ident_tail);
+            let slice = at.slice_between(end).unwrap();
+            let start = at.at - 1;
+            let end_pos = at.at + slice.len();
+            Some((Substitution::Name(slice, (start, end_pos)), end.slice_after()))
+        }
+    }
+
+    fn at_next_cp_while<F>(mut cur: Cur<'_>, mut pred: F) -> Cur<'_>
+    where
+        F: FnMut(char) -> bool,
+    {
+        loop {
+            match cur.next_cp() {
+                Some((c, next)) => {
+                    if pred(c) {
+                        cur = next;
+                    } else {
+                        return cur;
+                    }
+                }
+                None => return cur,
+            }
+        }
+    }
+
+    fn is_ident_head(c: char) -> bool {
+        match c {
+            'a'..='z' | 'A'..='Z' | '_' => true,
+            _ => false,
+        }
+    }
+
+    fn is_ident_tail(c: char) -> bool {
+        match c {
+            '0'..='9' => true,
+            c => is_ident_head(c),
+        }
+    }
+
+    #[cfg(test)]
+    mod tests;
+}
+
+mod strcursor {
+    pub struct StrCursor<'a> {
+        s: &'a str,
+        pub at: usize,
+    }
+
+    impl<'a> StrCursor<'a> {
+        pub fn new_at(s: &'a str, at: usize) -> StrCursor<'a> {
+            StrCursor { s, at }
+        }
+
+        pub fn at_next_cp(mut self) -> Option<StrCursor<'a>> {
+            match self.try_seek_right_cp() {
+                true => Some(self),
+                false => None,
+            }
+        }
+
+        pub fn next_cp(mut self) -> Option<(char, StrCursor<'a>)> {
+            let cp = self.cp_after()?;
+            self.seek_right(cp.len_utf8());
+            Some((cp, self))
+        }
+
+        fn slice_before(&self) -> &'a str {
+            &self.s[0..self.at]
+        }
+
+        pub fn slice_after(&self) -> &'a str {
+            &self.s[self.at..]
+        }
+
+        pub fn slice_between(&self, until: StrCursor<'a>) -> Option<&'a str> {
+            if !str_eq_literal(self.s, until.s) {
+                None
+            } else {
+                use std::cmp::{max, min};
+                let beg = min(self.at, until.at);
+                let end = max(self.at, until.at);
+                Some(&self.s[beg..end])
+            }
+        }
+
+        fn cp_after(&self) -> Option<char> {
+            self.slice_after().chars().next()
+        }
+
+        fn try_seek_right_cp(&mut self) -> bool {
+            match self.slice_after().chars().next() {
+                Some(c) => {
+                    self.at += c.len_utf8();
+                    true
+                }
+                None => false,
+            }
+        }
+
+        fn seek_right(&mut self, bytes: usize) {
+            self.at += bytes;
+        }
+    }
+
+    impl Copy for StrCursor<'_> {}
+
+    impl<'a> Clone for StrCursor<'a> {
+        fn clone(&self) -> StrCursor<'a> {
+            *self
+        }
+    }
+
+    impl std::fmt::Debug for StrCursor<'_> {
+        fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            write!(fmt, "StrCursor({:?} | {:?})", self.slice_before(), self.slice_after())
+        }
+    }
+
+    fn str_eq_literal(a: &str, b: &str) -> bool {
+        a.as_bytes().as_ptr() == b.as_bytes().as_ptr() && a.len() == b.len()
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/format_foreign/printf/tests.rs b/compiler/rustc_builtin_macros/src/format_foreign/printf/tests.rs
new file mode 100644
index 00000000000..33c54c9cee0
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/format_foreign/printf/tests.rs
@@ -0,0 +1,145 @@
+use super::{iter_subs, parse_next_substitution as pns, Format as F, Num as N, Substitution as S};
+
+macro_rules! assert_eq_pnsat {
+    ($lhs:expr, $rhs:expr) => {
+        assert_eq!(
+            pns($lhs).and_then(|(s, _)| s.translate()),
+            $rhs.map(<String as From<&str>>::from)
+        )
+    };
+}
+
+#[test]
+fn test_escape() {
+    assert_eq!(pns("has no escapes"), None);
+    assert_eq!(pns("has no escapes, either %"), None);
+    assert_eq!(pns("*so* has a %% escape"), Some((S::Escape, " escape")));
+    assert_eq!(pns("%% leading escape"), Some((S::Escape, " leading escape")));
+    assert_eq!(pns("trailing escape %%"), Some((S::Escape, "")));
+}
+
+#[test]
+fn test_parse() {
+    macro_rules! assert_pns_eq_sub {
+        ($in_:expr, {
+            $param:expr, $flags:expr,
+            $width:expr, $prec:expr, $len:expr, $type_:expr,
+            $pos:expr,
+        }) => {
+            assert_eq!(
+                pns(concat!($in_, "!")),
+                Some((
+                    S::Format(F {
+                        span: $in_,
+                        parameter: $param,
+                        flags: $flags,
+                        width: $width,
+                        precision: $prec,
+                        length: $len,
+                        type_: $type_,
+                        position: rustc_span::InnerSpan::new($pos.0, $pos.1),
+                    }),
+                    "!"
+                ))
+            )
+        };
+    }
+
+    assert_pns_eq_sub!("%!",
+        { None, "", None, None, None, "!", (0, 2), });
+    assert_pns_eq_sub!("%c",
+        { None, "", None, None, None, "c", (0, 2), });
+    assert_pns_eq_sub!("%s",
+        { None, "", None, None, None, "s", (0, 2), });
+    assert_pns_eq_sub!("%06d",
+        { None, "0", Some(N::Num(6)), None, None, "d", (0, 4), });
+    assert_pns_eq_sub!("%4.2f",
+        { None, "", Some(N::Num(4)), Some(N::Num(2)), None, "f", (0, 5), });
+    assert_pns_eq_sub!("%#x",
+        { None, "#", None, None, None, "x", (0, 3), });
+    assert_pns_eq_sub!("%-10s",
+        { None, "-", Some(N::Num(10)), None, None, "s", (0, 5), });
+    assert_pns_eq_sub!("%*s",
+        { None, "", Some(N::Next), None, None, "s", (0, 3), });
+    assert_pns_eq_sub!("%-10.*s",
+        { None, "-", Some(N::Num(10)), Some(N::Next), None, "s", (0, 7), });
+    assert_pns_eq_sub!("%-*.*s",
+        { None, "-", Some(N::Next), Some(N::Next), None, "s", (0, 6), });
+    assert_pns_eq_sub!("%.6i",
+        { None, "", None, Some(N::Num(6)), None, "i", (0, 4), });
+    assert_pns_eq_sub!("%+i",
+        { None, "+", None, None, None, "i", (0, 3), });
+    assert_pns_eq_sub!("%08X",
+        { None, "0", Some(N::Num(8)), None, None, "X", (0, 4), });
+    assert_pns_eq_sub!("%lu",
+        { None, "", None, None, Some("l"), "u", (0, 3), });
+    assert_pns_eq_sub!("%Iu",
+        { None, "", None, None, Some("I"), "u", (0, 3), });
+    assert_pns_eq_sub!("%I32u",
+        { None, "", None, None, Some("I32"), "u", (0, 5), });
+    assert_pns_eq_sub!("%I64u",
+        { None, "", None, None, Some("I64"), "u", (0, 5), });
+    assert_pns_eq_sub!("%'d",
+        { None, "'", None, None, None, "d", (0, 3), });
+    assert_pns_eq_sub!("%10s",
+        { None, "", Some(N::Num(10)), None, None, "s", (0, 4), });
+    assert_pns_eq_sub!("%-10.10s",
+        { None, "-", Some(N::Num(10)), Some(N::Num(10)), None, "s", (0, 8), });
+    assert_pns_eq_sub!("%1$d",
+        { Some(1), "", None, None, None, "d", (0, 4), });
+    assert_pns_eq_sub!("%2$.*3$d",
+        { Some(2), "", None, Some(N::Arg(3)), None, "d", (0, 8), });
+    assert_pns_eq_sub!("%1$*2$.*3$d",
+        { Some(1), "", Some(N::Arg(2)), Some(N::Arg(3)), None, "d", (0, 11), });
+    assert_pns_eq_sub!("%-8ld",
+        { None, "-", Some(N::Num(8)), None, Some("l"), "d", (0, 5), });
+}
+
+#[test]
+fn test_iter() {
+    let s = "The %d'th word %% is: `%.*s` %!\n";
+    let subs: Vec<_> = iter_subs(s, 0).map(|sub| sub.translate()).collect();
+    assert_eq!(
+        subs.iter().map(|ms| ms.as_ref().map(|s| &s[..])).collect::<Vec<_>>(),
+        vec![Some("{}"), None, Some("{:.*}"), None]
+    );
+}
+
+/// Checks that the translations are what we expect.
+#[test]
+fn test_translation() {
+    assert_eq_pnsat!("%c", Some("{}"));
+    assert_eq_pnsat!("%d", Some("{}"));
+    assert_eq_pnsat!("%u", Some("{}"));
+    assert_eq_pnsat!("%x", Some("{:x}"));
+    assert_eq_pnsat!("%X", Some("{:X}"));
+    assert_eq_pnsat!("%e", Some("{:e}"));
+    assert_eq_pnsat!("%E", Some("{:E}"));
+    assert_eq_pnsat!("%f", Some("{}"));
+    assert_eq_pnsat!("%g", Some("{:e}"));
+    assert_eq_pnsat!("%G", Some("{:E}"));
+    assert_eq_pnsat!("%s", Some("{}"));
+    assert_eq_pnsat!("%p", Some("{:p}"));
+
+    assert_eq_pnsat!("%06d", Some("{:06}"));
+    assert_eq_pnsat!("%4.2f", Some("{:4.2}"));
+    assert_eq_pnsat!("%#x", Some("{:#x}"));
+    assert_eq_pnsat!("%-10s", Some("{:<10}"));
+    assert_eq_pnsat!("%*s", None);
+    assert_eq_pnsat!("%-10.*s", Some("{:<10.*}"));
+    assert_eq_pnsat!("%-*.*s", None);
+    assert_eq_pnsat!("%.6i", Some("{:06}"));
+    assert_eq_pnsat!("%+i", Some("{:+}"));
+    assert_eq_pnsat!("%08X", Some("{:08X}"));
+    assert_eq_pnsat!("%lu", Some("{}"));
+    assert_eq_pnsat!("%Iu", Some("{}"));
+    assert_eq_pnsat!("%I32u", Some("{}"));
+    assert_eq_pnsat!("%I64u", Some("{}"));
+    assert_eq_pnsat!("%'d", None);
+    assert_eq_pnsat!("%10s", Some("{:>10}"));
+    assert_eq_pnsat!("%-10.10s", Some("{:<10.10}"));
+    assert_eq_pnsat!("%1$d", Some("{0}"));
+    assert_eq_pnsat!("%2$.*3$d", Some("{1:02$}"));
+    assert_eq_pnsat!("%1$*2$.*3$s", Some("{0:>1$.2$}"));
+    assert_eq_pnsat!("%-8ld", Some("{:<8}"));
+}
diff --git a/compiler/rustc_builtin_macros/src/format_foreign/shell/tests.rs b/compiler/rustc_builtin_macros/src/format_foreign/shell/tests.rs
new file mode 100644
index 00000000000..ed8fe81dfcd
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/format_foreign/shell/tests.rs
@@ -0,0 +1,56 @@
+use super::{parse_next_substitution as pns, Substitution as S};
+
+macro_rules! assert_eq_pnsat {
+    ($lhs:expr, $rhs:expr) => {
+        assert_eq!(
+            pns($lhs).and_then(|(f, _)| f.translate()),
+            $rhs.map(<String as From<&str>>::from)
+        )
+    };
+}
+
+#[test]
+fn test_escape() {
+    assert_eq!(pns("has no escapes"), None);
+    assert_eq!(pns("has no escapes, either $"), None);
+    assert_eq!(pns("*so* has a $$ escape"), Some((S::Escape((11, 13)), " escape")));
+    assert_eq!(pns("$$ leading escape"), Some((S::Escape((0, 2)), " leading escape")));
+    assert_eq!(pns("trailing escape $$"), Some((S::Escape((16, 18)), "")));
+}
+
+#[test]
+fn test_parse() {
+    macro_rules! assert_pns_eq_sub {
+        ($in_:expr, $kind:ident($arg:expr, $pos:expr)) => {
+            assert_eq!(pns(concat!($in_, "!")), Some((S::$kind($arg.into(), $pos), "!")))
+        };
+    }
+
+    assert_pns_eq_sub!("$0", Ordinal(0, (0, 2)));
+    assert_pns_eq_sub!("$1", Ordinal(1, (0, 2)));
+    assert_pns_eq_sub!("$9", Ordinal(9, (0, 2)));
+    assert_pns_eq_sub!("$N", Name("N", (0, 2)));
+    assert_pns_eq_sub!("$NAME", Name("NAME", (0, 5)));
+}
+
+#[test]
+fn test_iter() {
+    use super::iter_subs;
+    let s = "The $0'th word $$ is: `$WORD` $!\n";
+    let subs: Vec<_> = iter_subs(s, 0).map(|sub| sub.translate()).collect();
+    assert_eq!(
+        subs.iter().map(|ms| ms.as_ref().map(|s| &s[..])).collect::<Vec<_>>(),
+        vec![Some("{0}"), None, Some("{WORD}")]
+    );
+}
+
+#[test]
+fn test_translation() {
+    assert_eq_pnsat!("$0", Some("{0}"));
+    assert_eq_pnsat!("$9", Some("{9}"));
+    assert_eq_pnsat!("$1", Some("{1}"));
+    assert_eq_pnsat!("$10", Some("{1}"));
+    assert_eq_pnsat!("$stuff", Some("{stuff}"));
+    assert_eq_pnsat!("$NAME", Some("{NAME}"));
+    assert_eq_pnsat!("$PREFIX/bin", Some("{PREFIX}"));
+}
diff --git a/compiler/rustc_builtin_macros/src/global_allocator.rs b/compiler/rustc_builtin_macros/src/global_allocator.rs
new file mode 100644
index 00000000000..8478fcfbf09
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/global_allocator.rs
@@ -0,0 +1,171 @@
+use crate::util::check_builtin_macro_attribute;
+
+use rustc_ast::expand::allocator::{
+    AllocatorKind, AllocatorMethod, AllocatorTy, ALLOCATOR_METHODS,
+};
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, Attribute, Expr, FnHeader, FnSig, Generics, Param};
+use rustc_ast::{ItemKind, Mutability, Stmt, Ty, TyKind, Unsafe};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::Span;
+
+pub fn expand(
+    ecx: &mut ExtCtxt<'_>,
+    _span: Span,
+    meta_item: &ast::MetaItem,
+    item: Annotatable,
+) -> Vec<Annotatable> {
+    check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);
+
+    let not_static = |item: Annotatable| {
+        ecx.sess.parse_sess.span_diagnostic.span_err(item.span(), "allocators must be statics");
+        vec![item]
+    };
+    let item = match item {
+        Annotatable::Item(item) => match item.kind {
+            ItemKind::Static(..) => item,
+            _ => return not_static(Annotatable::Item(item)),
+        },
+        _ => return not_static(item),
+    };
+
+    // Generate a bunch of new items using the AllocFnFactory
+    let span = ecx.with_def_site_ctxt(item.span);
+    let f = AllocFnFactory { span, kind: AllocatorKind::Global, global: item.ident, cx: ecx };
+
+    // Generate item statements for the allocator methods.
+    let stmts = ALLOCATOR_METHODS.iter().map(|method| f.allocator_fn(method)).collect();
+
+    // Generate anonymous constant serving as container for the allocator methods.
+    let const_ty = ecx.ty(span, TyKind::Tup(Vec::new()));
+    let const_body = ecx.expr_block(ecx.block(span, stmts));
+    let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
+
+    // Return the original item and the new methods.
+    vec![Annotatable::Item(item), Annotatable::Item(const_item)]
+}
+
+struct AllocFnFactory<'a, 'b> {
+    span: Span,
+    kind: AllocatorKind,
+    global: Ident,
+    cx: &'b ExtCtxt<'a>,
+}
+
+impl AllocFnFactory<'_, '_> {
+    fn allocator_fn(&self, method: &AllocatorMethod) -> Stmt {
+        let mut abi_args = Vec::new();
+        let mut i = 0;
+        let mut mk = || {
+            let name = Ident::from_str_and_span(&format!("arg{}", i), self.span);
+            i += 1;
+            name
+        };
+        let args = method.inputs.iter().map(|ty| self.arg_ty(ty, &mut abi_args, &mut mk)).collect();
+        let result = self.call_allocator(method.name, args);
+        let (output_ty, output_expr) = self.ret_ty(&method.output, result);
+        let decl = self.cx.fn_decl(abi_args, ast::FnRetTy::Ty(output_ty));
+        let header = FnHeader { unsafety: Unsafe::Yes(self.span), ..FnHeader::default() };
+        let sig = FnSig { decl, header, span: self.span };
+        let block = Some(self.cx.block_expr(output_expr));
+        let kind = ItemKind::Fn(ast::Defaultness::Final, sig, Generics::default(), block);
+        let item = self.cx.item(
+            self.span,
+            Ident::from_str_and_span(&self.kind.fn_name(method.name), self.span),
+            self.attrs(),
+            kind,
+        );
+        self.cx.stmt_item(self.span, item)
+    }
+
+    fn call_allocator(&self, method: Symbol, mut args: Vec<P<Expr>>) -> P<Expr> {
+        let method = self.cx.std_path(&[sym::alloc, sym::GlobalAlloc, method]);
+        let method = self.cx.expr_path(self.cx.path(self.span, method));
+        let allocator = self.cx.path_ident(self.span, self.global);
+        let allocator = self.cx.expr_path(allocator);
+        let allocator = self.cx.expr_addr_of(self.span, allocator);
+        args.insert(0, allocator);
+
+        self.cx.expr_call(self.span, method, args)
+    }
+
+    fn attrs(&self) -> Vec<Attribute> {
+        let special = sym::rustc_std_internal_symbol;
+        let special = self.cx.meta_word(self.span, special);
+        vec![self.cx.attribute(special)]
+    }
+
+    fn arg_ty(
+        &self,
+        ty: &AllocatorTy,
+        args: &mut Vec<Param>,
+        ident: &mut dyn FnMut() -> Ident,
+    ) -> P<Expr> {
+        match *ty {
+            AllocatorTy::Layout => {
+                let usize = self.cx.path_ident(self.span, Ident::new(sym::usize, self.span));
+                let ty_usize = self.cx.ty_path(usize);
+                let size = ident();
+                let align = ident();
+                args.push(self.cx.param(self.span, size, ty_usize.clone()));
+                args.push(self.cx.param(self.span, align, ty_usize));
+
+                let layout_new =
+                    self.cx.std_path(&[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
+                let layout_new = self.cx.expr_path(self.cx.path(self.span, layout_new));
+                let size = self.cx.expr_ident(self.span, size);
+                let align = self.cx.expr_ident(self.span, align);
+                let layout = self.cx.expr_call(self.span, layout_new, vec![size, align]);
+                layout
+            }
+
+            AllocatorTy::Ptr => {
+                let ident = ident();
+                args.push(self.cx.param(self.span, ident, self.ptr_u8()));
+                let arg = self.cx.expr_ident(self.span, ident);
+                self.cx.expr_cast(self.span, arg, self.ptr_u8())
+            }
+
+            AllocatorTy::Usize => {
+                let ident = ident();
+                args.push(self.cx.param(self.span, ident, self.usize()));
+                self.cx.expr_ident(self.span, ident)
+            }
+
+            AllocatorTy::ResultPtr | AllocatorTy::Unit => {
+                panic!("can't convert AllocatorTy to an argument")
+            }
+        }
+    }
+
+    fn ret_ty(&self, ty: &AllocatorTy, expr: P<Expr>) -> (P<Ty>, P<Expr>) {
+        match *ty {
+            AllocatorTy::ResultPtr => {
+                // We're creating:
+                //
+                //      #expr as *mut u8
+
+                let expr = self.cx.expr_cast(self.span, expr, self.ptr_u8());
+                (self.ptr_u8(), expr)
+            }
+
+            AllocatorTy::Unit => (self.cx.ty(self.span, TyKind::Tup(Vec::new())), expr),
+
+            AllocatorTy::Layout | AllocatorTy::Usize | AllocatorTy::Ptr => {
+                panic!("can't convert `AllocatorTy` to an output")
+            }
+        }
+    }
+
+    fn usize(&self) -> P<Ty> {
+        let usize = self.cx.path_ident(self.span, Ident::new(sym::usize, self.span));
+        self.cx.ty_path(usize)
+    }
+
+    fn ptr_u8(&self) -> P<Ty> {
+        let u8 = self.cx.path_ident(self.span, Ident::new(sym::u8, self.span));
+        let ty_u8 = self.cx.ty_path(u8);
+        self.cx.ty_ptr(self.span, ty_u8, Mutability::Mut)
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/global_asm.rs b/compiler/rustc_builtin_macros/src/global_asm.rs
new file mode 100644
index 00000000000..2465f33622e
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/global_asm.rs
@@ -0,0 +1,65 @@
+//! Module-level assembly support.
+//!
+//! The macro defined here allows you to specify "top-level",
+//! "file-scoped", or "module-level" assembly. These synonyms
+//! all correspond to LLVM's module-level inline assembly instruction.
+//!
+//! For example, `global_asm!("some assembly here")` codegens to
+//! LLVM's `module asm "some assembly here"`. All of LLVM's caveats
+//! therefore apply.
+
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_errors::DiagnosticBuilder;
+use rustc_expand::base::{self, *};
+use rustc_span::source_map::respan;
+use rustc_span::symbol::Ident;
+use rustc_span::Span;
+use smallvec::smallvec;
+
+pub fn expand_global_asm<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    match parse_global_asm(cx, sp, tts) {
+        Ok(Some(global_asm)) => MacEager::items(smallvec![P(ast::Item {
+            ident: Ident::invalid(),
+            attrs: Vec::new(),
+            id: ast::DUMMY_NODE_ID,
+            kind: ast::ItemKind::GlobalAsm(P(global_asm)),
+            vis: respan(sp.shrink_to_lo(), ast::VisibilityKind::Inherited),
+            span: cx.with_def_site_ctxt(sp),
+            tokens: None,
+        })]),
+        Ok(None) => DummyResult::any(sp),
+        Err(mut err) => {
+            err.emit();
+            DummyResult::any(sp)
+        }
+    }
+}
+
+fn parse_global_asm<'a>(
+    cx: &mut ExtCtxt<'a>,
+    sp: Span,
+    tts: TokenStream,
+) -> Result<Option<ast::GlobalAsm>, DiagnosticBuilder<'a>> {
+    let mut p = cx.new_parser_from_tts(tts);
+
+    if p.token == token::Eof {
+        let mut err = cx.struct_span_err(sp, "macro requires a string literal as an argument");
+        err.span_label(sp, "string literal required");
+        return Err(err);
+    }
+
+    let expr = p.parse_expr()?;
+    let (asm, _) = match expr_to_string(cx, expr, "inline assembly must be a string literal") {
+        Some((s, st)) => (s, st),
+        None => return Ok(None),
+    };
+
+    Ok(Some(ast::GlobalAsm { asm }))
+}
diff --git a/compiler/rustc_builtin_macros/src/lib.rs b/compiler/rustc_builtin_macros/src/lib.rs
new file mode 100644
index 00000000000..87be6d1743a
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/lib.rs
@@ -0,0 +1,113 @@
+//! This crate contains implementations of built-in macros and other code generating facilities
+//! injecting code into the crate before it is lowered to HIR.
+
+#![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
+#![feature(bool_to_option)]
+#![feature(crate_visibility_modifier)]
+#![feature(decl_macro)]
+#![feature(nll)]
+#![feature(or_patterns)]
+#![feature(proc_macro_internals)]
+#![feature(proc_macro_quote)]
+
+extern crate proc_macro;
+
+use crate::deriving::*;
+
+use rustc_expand::base::{MacroExpanderFn, ResolverExpand, SyntaxExtension, SyntaxExtensionKind};
+use rustc_expand::proc_macro::BangProcMacro;
+use rustc_span::edition::Edition;
+use rustc_span::symbol::{sym, Ident};
+
+mod asm;
+mod assert;
+mod cfg;
+mod cfg_accessible;
+mod compile_error;
+mod concat;
+mod concat_idents;
+mod deriving;
+mod env;
+mod format;
+mod format_foreign;
+mod global_allocator;
+mod global_asm;
+mod llvm_asm;
+mod log_syntax;
+mod source_util;
+mod test;
+mod trace_macros;
+mod util;
+
+pub mod cmdline_attrs;
+pub mod proc_macro_harness;
+pub mod standard_library_imports;
+pub mod test_harness;
+
+pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand, edition: Edition) {
+    let mut register = |name, kind| {
+        resolver.register_builtin_macro(
+            Ident::with_dummy_span(name),
+            SyntaxExtension { is_builtin: true, ..SyntaxExtension::default(kind, edition) },
+        )
+    };
+    macro register_bang($($name:ident: $f:expr,)*) {
+        $(register(sym::$name, SyntaxExtensionKind::LegacyBang(Box::new($f as MacroExpanderFn)));)*
+    }
+    macro register_attr($($name:ident: $f:expr,)*) {
+        $(register(sym::$name, SyntaxExtensionKind::LegacyAttr(Box::new($f)));)*
+    }
+    macro register_derive($($name:ident: $f:expr,)*) {
+        $(register(sym::$name, SyntaxExtensionKind::LegacyDerive(Box::new(BuiltinDerive($f))));)*
+    }
+
+    register_bang! {
+        asm: asm::expand_asm,
+        assert: assert::expand_assert,
+        cfg: cfg::expand_cfg,
+        column: source_util::expand_column,
+        compile_error: compile_error::expand_compile_error,
+        concat_idents: concat_idents::expand_concat_idents,
+        concat: concat::expand_concat,
+        env: env::expand_env,
+        file: source_util::expand_file,
+        format_args_nl: format::expand_format_args_nl,
+        format_args: format::expand_format_args,
+        global_asm: global_asm::expand_global_asm,
+        include_bytes: source_util::expand_include_bytes,
+        include_str: source_util::expand_include_str,
+        include: source_util::expand_include,
+        line: source_util::expand_line,
+        llvm_asm: llvm_asm::expand_llvm_asm,
+        log_syntax: log_syntax::expand_log_syntax,
+        module_path: source_util::expand_mod,
+        option_env: env::expand_option_env,
+        stringify: source_util::expand_stringify,
+        trace_macros: trace_macros::expand_trace_macros,
+    }
+
+    register_attr! {
+        bench: test::expand_bench,
+        cfg_accessible: cfg_accessible::Expander,
+        global_allocator: global_allocator::expand,
+        test: test::expand_test,
+        test_case: test::expand_test_case,
+    }
+
+    register_derive! {
+        Clone: clone::expand_deriving_clone,
+        Copy: bounds::expand_deriving_copy,
+        Debug: debug::expand_deriving_debug,
+        Default: default::expand_deriving_default,
+        Eq: eq::expand_deriving_eq,
+        Hash: hash::expand_deriving_hash,
+        Ord: ord::expand_deriving_ord,
+        PartialEq: partial_eq::expand_deriving_partial_eq,
+        PartialOrd: partial_ord::expand_deriving_partial_ord,
+        RustcDecodable: decodable::expand_deriving_rustc_decodable,
+        RustcEncodable: encodable::expand_deriving_rustc_encodable,
+    }
+
+    let client = proc_macro::bridge::client::Client::expand1(proc_macro::quote);
+    register(sym::quote, SyntaxExtensionKind::Bang(Box::new(BangProcMacro { client })));
+}
diff --git a/compiler/rustc_builtin_macros/src/llvm_asm.rs b/compiler/rustc_builtin_macros/src/llvm_asm.rs
new file mode 100644
index 00000000000..db73fdbe24f
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/llvm_asm.rs
@@ -0,0 +1,301 @@
+// Llvm-style inline assembly support.
+//
+use State::*;
+
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Token};
+use rustc_ast::tokenstream::{self, TokenStream};
+use rustc_ast::LlvmAsmDialect;
+use rustc_errors::{struct_span_err, DiagnosticBuilder, PResult};
+use rustc_expand::base::*;
+use rustc_parse::parser::Parser;
+use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::Span;
+
+enum State {
+    Asm,
+    Outputs,
+    Inputs,
+    Clobbers,
+    Options,
+    StateNone,
+}
+
+impl State {
+    fn next(&self) -> State {
+        match *self {
+            Asm => Outputs,
+            Outputs => Inputs,
+            Inputs => Clobbers,
+            Clobbers => Options,
+            Options => StateNone,
+            StateNone => StateNone,
+        }
+    }
+}
+
+const OPTIONS: &[Symbol] = &[sym::volatile, sym::alignstack, sym::intel];
+
+pub fn expand_llvm_asm<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn MacResult + 'cx> {
+    let mut inline_asm = match parse_inline_asm(cx, sp, tts) {
+        Ok(Some(inline_asm)) => inline_asm,
+        Ok(None) => return DummyResult::any(sp),
+        Err(mut err) => {
+            err.emit();
+            return DummyResult::any(sp);
+        }
+    };
+
+    // If there are no outputs, the inline assembly is executed just for its side effects,
+    // so ensure that it is volatile
+    if inline_asm.outputs.is_empty() {
+        inline_asm.volatile = true;
+    }
+
+    MacEager::expr(P(ast::Expr {
+        id: ast::DUMMY_NODE_ID,
+        kind: ast::ExprKind::LlvmInlineAsm(P(inline_asm)),
+        span: cx.with_def_site_ctxt(sp),
+        attrs: ast::AttrVec::new(),
+        tokens: None,
+    }))
+}
+
+fn parse_asm_str<'a>(p: &mut Parser<'a>) -> PResult<'a, Symbol> {
+    match p.parse_str_lit() {
+        Ok(str_lit) => Ok(str_lit.symbol_unescaped),
+        Err(opt_lit) => {
+            let span = opt_lit.map_or(p.token.span, |lit| lit.span);
+            let mut err = p.sess.span_diagnostic.struct_span_err(span, "expected string literal");
+            err.span_label(span, "not a string literal");
+            Err(err)
+        }
+    }
+}
+
+fn parse_inline_asm<'a>(
+    cx: &mut ExtCtxt<'a>,
+    sp: Span,
+    tts: TokenStream,
+) -> Result<Option<ast::LlvmInlineAsm>, DiagnosticBuilder<'a>> {
+    // Split the tts before the first colon, to avoid `llvm_asm!("x": y)`  being
+    // parsed as `llvm_asm!(z)` with `z = "x": y` which is type ascription.
+    let first_colon = tts
+        .trees()
+        .position(|tt| match tt {
+            tokenstream::TokenTree::Token(Token { kind: token::Colon | token::ModSep, .. }) => true,
+            _ => false,
+        })
+        .unwrap_or(tts.len());
+    let mut p = cx.new_parser_from_tts(tts.trees().skip(first_colon).collect());
+    let mut asm = kw::Invalid;
+    let mut asm_str_style = None;
+    let mut outputs = Vec::new();
+    let mut inputs = Vec::new();
+    let mut clobs = Vec::new();
+    let mut volatile = false;
+    let mut alignstack = false;
+    let mut dialect = LlvmAsmDialect::Att;
+
+    let mut state = Asm;
+
+    'statement: loop {
+        match state {
+            Asm => {
+                if asm_str_style.is_some() {
+                    // If we already have a string with instructions,
+                    // ending up in Asm state again is an error.
+                    return Err(struct_span_err!(
+                        cx.sess.parse_sess.span_diagnostic,
+                        sp,
+                        E0660,
+                        "malformed inline assembly"
+                    ));
+                }
+                // Nested parser, stop before the first colon (see above).
+                let mut p2 = cx.new_parser_from_tts(tts.trees().take(first_colon).collect());
+
+                if p2.token == token::Eof {
+                    let mut err =
+                        cx.struct_span_err(sp, "macro requires a string literal as an argument");
+                    err.span_label(sp, "string literal required");
+                    return Err(err);
+                }
+
+                let expr = p2.parse_expr()?;
+                let (s, style) =
+                    match expr_to_string(cx, expr, "inline assembly must be a string literal") {
+                        Some((s, st)) => (s, st),
+                        None => return Ok(None),
+                    };
+
+                // This is most likely malformed.
+                if p2.token != token::Eof {
+                    let mut extra_tts = p2.parse_all_token_trees()?;
+                    extra_tts.extend(tts.trees().skip(first_colon));
+                    p = cx.new_parser_from_tts(extra_tts.into_iter().collect());
+                }
+
+                asm = s;
+                asm_str_style = Some(style);
+            }
+            Outputs => {
+                while p.token != token::Eof && p.token != token::Colon && p.token != token::ModSep {
+                    if !outputs.is_empty() {
+                        p.eat(&token::Comma);
+                    }
+
+                    let constraint = parse_asm_str(&mut p)?;
+
+                    let span = p.prev_token.span;
+
+                    p.expect(&token::OpenDelim(token::Paren))?;
+                    let expr = p.parse_expr()?;
+                    p.expect(&token::CloseDelim(token::Paren))?;
+
+                    // Expands a read+write operand into two operands.
+                    //
+                    // Use '+' modifier when you want the same expression
+                    // to be both an input and an output at the same time.
+                    // It's the opposite of '=&' which means that the memory
+                    // cannot be shared with any other operand (usually when
+                    // a register is clobbered early.)
+                    let constraint_str = constraint.as_str();
+                    let mut ch = constraint_str.chars();
+                    let output = match ch.next() {
+                        Some('=') => None,
+                        Some('+') => Some(Symbol::intern(&format!("={}", ch.as_str()))),
+                        _ => {
+                            struct_span_err!(
+                                cx.sess.parse_sess.span_diagnostic,
+                                span,
+                                E0661,
+                                "output operand constraint lacks '=' or '+'"
+                            )
+                            .emit();
+                            None
+                        }
+                    };
+
+                    let is_rw = output.is_some();
+                    let is_indirect = constraint_str.contains('*');
+                    outputs.push(ast::LlvmInlineAsmOutput {
+                        constraint: output.unwrap_or(constraint),
+                        expr,
+                        is_rw,
+                        is_indirect,
+                    });
+                }
+            }
+            Inputs => {
+                while p.token != token::Eof && p.token != token::Colon && p.token != token::ModSep {
+                    if !inputs.is_empty() {
+                        p.eat(&token::Comma);
+                    }
+
+                    let constraint = parse_asm_str(&mut p)?;
+
+                    if constraint.as_str().starts_with('=') {
+                        struct_span_err!(
+                            cx.sess.parse_sess.span_diagnostic,
+                            p.prev_token.span,
+                            E0662,
+                            "input operand constraint contains '='"
+                        )
+                        .emit();
+                    } else if constraint.as_str().starts_with('+') {
+                        struct_span_err!(
+                            cx.sess.parse_sess.span_diagnostic,
+                            p.prev_token.span,
+                            E0663,
+                            "input operand constraint contains '+'"
+                        )
+                        .emit();
+                    }
+
+                    p.expect(&token::OpenDelim(token::Paren))?;
+                    let input = p.parse_expr()?;
+                    p.expect(&token::CloseDelim(token::Paren))?;
+
+                    inputs.push((constraint, input));
+                }
+            }
+            Clobbers => {
+                while p.token != token::Eof && p.token != token::Colon && p.token != token::ModSep {
+                    if !clobs.is_empty() {
+                        p.eat(&token::Comma);
+                    }
+
+                    let s = parse_asm_str(&mut p)?;
+
+                    if OPTIONS.iter().any(|&opt| s == opt) {
+                        cx.span_warn(p.prev_token.span, "expected a clobber, found an option");
+                    } else if s.as_str().starts_with('{') || s.as_str().ends_with('}') {
+                        struct_span_err!(
+                            cx.sess.parse_sess.span_diagnostic,
+                            p.prev_token.span,
+                            E0664,
+                            "clobber should not be surrounded by braces"
+                        )
+                        .emit();
+                    }
+
+                    clobs.push(s);
+                }
+            }
+            Options => {
+                let option = parse_asm_str(&mut p)?;
+
+                if option == sym::volatile {
+                    // Indicates that the inline assembly has side effects
+                    // and must not be optimized out along with its outputs.
+                    volatile = true;
+                } else if option == sym::alignstack {
+                    alignstack = true;
+                } else if option == sym::intel {
+                    dialect = LlvmAsmDialect::Intel;
+                } else {
+                    cx.span_warn(p.prev_token.span, "unrecognized option");
+                }
+
+                if p.token == token::Comma {
+                    p.eat(&token::Comma);
+                }
+            }
+            StateNone => (),
+        }
+
+        loop {
+            // MOD_SEP is a double colon '::' without space in between.
+            // When encountered, the state must be advanced twice.
+            match (&p.token.kind, state.next(), state.next().next()) {
+                (&token::Colon, StateNone, _) | (&token::ModSep, _, StateNone) => {
+                    p.bump();
+                    break 'statement;
+                }
+                (&token::Colon, st, _) | (&token::ModSep, _, st) => {
+                    p.bump();
+                    state = st;
+                }
+                (&token::Eof, ..) => break 'statement,
+                _ => break,
+            }
+        }
+    }
+
+    Ok(Some(ast::LlvmInlineAsm {
+        asm,
+        asm_str_style: asm_str_style.unwrap(),
+        outputs,
+        inputs,
+        clobbers: clobs,
+        volatile,
+        alignstack,
+        dialect,
+    }))
+}
diff --git a/compiler/rustc_builtin_macros/src/log_syntax.rs b/compiler/rustc_builtin_macros/src/log_syntax.rs
new file mode 100644
index 00000000000..ede34a76125
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/log_syntax.rs
@@ -0,0 +1,14 @@
+use rustc_ast::tokenstream::TokenStream;
+use rustc_ast_pretty::pprust;
+use rustc_expand::base;
+
+pub fn expand_log_syntax<'cx>(
+    _cx: &'cx mut base::ExtCtxt<'_>,
+    sp: rustc_span::Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    println!("{}", pprust::tts_to_string(&tts));
+
+    // any so that `log_syntax` can be invoked as an expression and item.
+    base::DummyResult::any_valid(sp)
+}
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
new file mode 100644
index 00000000000..0c6769906f3
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -0,0 +1,492 @@
+use std::mem;
+
+use rustc_ast::attr;
+use rustc_ast::ptr::P;
+use rustc_ast::visit::{self, Visitor};
+use rustc_ast::{self as ast, NodeId};
+use rustc_ast_pretty::pprust;
+use rustc_expand::base::{ExtCtxt, ResolverExpand};
+use rustc_expand::expand::{AstFragment, ExpansionConfig};
+use rustc_session::Session;
+use rustc_span::hygiene::AstPass;
+use rustc_span::source_map::SourceMap;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+use smallvec::smallvec;
+use std::cell::RefCell;
+
+struct ProcMacroDerive {
+    id: NodeId,
+    trait_name: Symbol,
+    function_name: Ident,
+    span: Span,
+    attrs: Vec<Symbol>,
+}
+
+enum ProcMacroDefType {
+    Attr,
+    Bang,
+}
+
+struct ProcMacroDef {
+    id: NodeId,
+    function_name: Ident,
+    span: Span,
+    def_type: ProcMacroDefType,
+}
+
+enum ProcMacro {
+    Derive(ProcMacroDerive),
+    Def(ProcMacroDef),
+}
+
+struct CollectProcMacros<'a> {
+    sess: &'a Session,
+    macros: Vec<ProcMacro>,
+    in_root: bool,
+    handler: &'a rustc_errors::Handler,
+    source_map: &'a SourceMap,
+    is_proc_macro_crate: bool,
+    is_test_crate: bool,
+}
+
+pub fn inject(
+    sess: &Session,
+    resolver: &mut dyn ResolverExpand,
+    mut krate: ast::Crate,
+    is_proc_macro_crate: bool,
+    has_proc_macro_decls: bool,
+    is_test_crate: bool,
+    num_crate_types: usize,
+    handler: &rustc_errors::Handler,
+) -> ast::Crate {
+    let ecfg = ExpansionConfig::default("proc_macro".to_string());
+    let mut cx = ExtCtxt::new(sess, ecfg, resolver, None);
+
+    let mut collect = CollectProcMacros {
+        sess,
+        macros: Vec::new(),
+        in_root: true,
+        handler,
+        source_map: sess.source_map(),
+        is_proc_macro_crate,
+        is_test_crate,
+    };
+
+    if has_proc_macro_decls || is_proc_macro_crate {
+        visit::walk_crate(&mut collect, &krate);
+    }
+    let macros = collect.macros;
+
+    if !is_proc_macro_crate {
+        return krate;
+    }
+
+    if num_crate_types > 1 {
+        handler.err("cannot mix `proc-macro` crate type with others");
+    }
+
+    if is_test_crate {
+        return krate;
+    }
+
+    let decls = mk_decls(&mut krate, &mut cx, &macros);
+    krate.module.items.push(decls);
+
+    krate
+}
+
+impl<'a> CollectProcMacros<'a> {
+    fn check_not_pub_in_root(&self, vis: &ast::Visibility, sp: Span) {
+        if self.is_proc_macro_crate && self.in_root && vis.node.is_pub() {
+            self.handler.span_err(
+                sp,
+                "`proc-macro` crate types currently cannot export any items other \
+                    than functions tagged with `#[proc_macro]`, `#[proc_macro_derive]`, \
+                    or `#[proc_macro_attribute]`",
+            );
+        }
+    }
+
+    fn collect_custom_derive(&mut self, item: &'a ast::Item, attr: &'a ast::Attribute) {
+        // Once we've located the `#[proc_macro_derive]` attribute, verify
+        // that it's of the form `#[proc_macro_derive(Foo)]` or
+        // `#[proc_macro_derive(Foo, attributes(A, ..))]`
+        let list = match attr.meta_item_list() {
+            Some(list) => list,
+            None => return,
+        };
+        if list.len() != 1 && list.len() != 2 {
+            self.handler.span_err(attr.span, "attribute must have either one or two arguments");
+            return;
+        }
+        let trait_attr = match list[0].meta_item() {
+            Some(meta_item) => meta_item,
+            _ => {
+                self.handler.span_err(list[0].span(), "not a meta item");
+                return;
+            }
+        };
+        let trait_ident = match trait_attr.ident() {
+            Some(trait_ident) if trait_attr.is_word() => trait_ident,
+            _ => {
+                self.handler.span_err(trait_attr.span, "must only be one word");
+                return;
+            }
+        };
+
+        if !trait_ident.name.can_be_raw() {
+            self.handler.span_err(
+                trait_attr.span,
+                &format!("`{}` cannot be a name of derive macro", trait_ident),
+            );
+        }
+
+        let attributes_attr = list.get(1);
+        let proc_attrs: Vec<_> = if let Some(attr) = attributes_attr {
+            if !attr.has_name(sym::attributes) {
+                self.handler.span_err(attr.span(), "second argument must be `attributes`")
+            }
+            attr.meta_item_list()
+                .unwrap_or_else(|| {
+                    self.handler
+                        .span_err(attr.span(), "attribute must be of form: `attributes(foo, bar)`");
+                    &[]
+                })
+                .iter()
+                .filter_map(|attr| {
+                    let attr = match attr.meta_item() {
+                        Some(meta_item) => meta_item,
+                        _ => {
+                            self.handler.span_err(attr.span(), "not a meta item");
+                            return None;
+                        }
+                    };
+
+                    let ident = match attr.ident() {
+                        Some(ident) if attr.is_word() => ident,
+                        _ => {
+                            self.handler.span_err(attr.span, "must only be one word");
+                            return None;
+                        }
+                    };
+                    if !ident.name.can_be_raw() {
+                        self.handler.span_err(
+                            attr.span,
+                            &format!("`{}` cannot be a name of derive helper attribute", ident),
+                        );
+                    }
+
+                    Some(ident.name)
+                })
+                .collect()
+        } else {
+            Vec::new()
+        };
+
+        if self.in_root && item.vis.node.is_pub() {
+            self.macros.push(ProcMacro::Derive(ProcMacroDerive {
+                id: item.id,
+                span: item.span,
+                trait_name: trait_ident.name,
+                function_name: item.ident,
+                attrs: proc_attrs,
+            }));
+        } else {
+            let msg = if !self.in_root {
+                "functions tagged with `#[proc_macro_derive]` must \
+                 currently reside in the root of the crate"
+            } else {
+                "functions tagged with `#[proc_macro_derive]` must be `pub`"
+            };
+            self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
+        }
+    }
+
+    fn collect_attr_proc_macro(&mut self, item: &'a ast::Item) {
+        if self.in_root && item.vis.node.is_pub() {
+            self.macros.push(ProcMacro::Def(ProcMacroDef {
+                id: item.id,
+                span: item.span,
+                function_name: item.ident,
+                def_type: ProcMacroDefType::Attr,
+            }));
+        } else {
+            let msg = if !self.in_root {
+                "functions tagged with `#[proc_macro_attribute]` must \
+                 currently reside in the root of the crate"
+            } else {
+                "functions tagged with `#[proc_macro_attribute]` must be `pub`"
+            };
+            self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
+        }
+    }
+
+    fn collect_bang_proc_macro(&mut self, item: &'a ast::Item) {
+        if self.in_root && item.vis.node.is_pub() {
+            self.macros.push(ProcMacro::Def(ProcMacroDef {
+                id: item.id,
+                span: item.span,
+                function_name: item.ident,
+                def_type: ProcMacroDefType::Bang,
+            }));
+        } else {
+            let msg = if !self.in_root {
+                "functions tagged with `#[proc_macro]` must \
+                 currently reside in the root of the crate"
+            } else {
+                "functions tagged with `#[proc_macro]` must be `pub`"
+            };
+            self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
+        }
+    }
+}
+
+impl<'a> Visitor<'a> for CollectProcMacros<'a> {
+    fn visit_item(&mut self, item: &'a ast::Item) {
+        if let ast::ItemKind::MacroDef(..) = item.kind {
+            if self.is_proc_macro_crate && self.sess.contains_name(&item.attrs, sym::macro_export) {
+                let msg =
+                    "cannot export macro_rules! macros from a `proc-macro` crate type currently";
+                self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
+            }
+        }
+
+        // First up, make sure we're checking a bare function. If we're not then
+        // we're just not interested in this item.
+        //
+        // If we find one, try to locate a `#[proc_macro_derive]` attribute on it.
+        let is_fn = match item.kind {
+            ast::ItemKind::Fn(..) => true,
+            _ => false,
+        };
+
+        let mut found_attr: Option<&'a ast::Attribute> = None;
+
+        for attr in &item.attrs {
+            if self.sess.is_proc_macro_attr(&attr) {
+                if let Some(prev_attr) = found_attr {
+                    let prev_item = prev_attr.get_normal_item();
+                    let item = attr.get_normal_item();
+                    let path_str = pprust::path_to_string(&item.path);
+                    let msg = if item.path.segments[0].ident.name
+                        == prev_item.path.segments[0].ident.name
+                    {
+                        format!(
+                            "only one `#[{}]` attribute is allowed on any given function",
+                            path_str,
+                        )
+                    } else {
+                        format!(
+                            "`#[{}]` and `#[{}]` attributes cannot both be applied
+                            to the same function",
+                            path_str,
+                            pprust::path_to_string(&prev_item.path),
+                        )
+                    };
+
+                    self.handler
+                        .struct_span_err(attr.span, &msg)
+                        .span_label(prev_attr.span, "previous attribute here")
+                        .emit();
+
+                    return;
+                }
+
+                found_attr = Some(attr);
+            }
+        }
+
+        let attr = match found_attr {
+            None => {
+                self.check_not_pub_in_root(&item.vis, self.source_map.guess_head_span(item.span));
+                let prev_in_root = mem::replace(&mut self.in_root, false);
+                visit::walk_item(self, item);
+                self.in_root = prev_in_root;
+                return;
+            }
+            Some(attr) => attr,
+        };
+
+        if !is_fn {
+            let msg = format!(
+                "the `#[{}]` attribute may only be used on bare functions",
+                pprust::path_to_string(&attr.get_normal_item().path),
+            );
+
+            self.handler.span_err(attr.span, &msg);
+            return;
+        }
+
+        if self.is_test_crate {
+            return;
+        }
+
+        if !self.is_proc_macro_crate {
+            let msg = format!(
+                "the `#[{}]` attribute is only usable with crates of the `proc-macro` crate type",
+                pprust::path_to_string(&attr.get_normal_item().path),
+            );
+
+            self.handler.span_err(attr.span, &msg);
+            return;
+        }
+
+        if self.sess.check_name(attr, sym::proc_macro_derive) {
+            self.collect_custom_derive(item, attr);
+        } else if self.sess.check_name(attr, sym::proc_macro_attribute) {
+            self.collect_attr_proc_macro(item);
+        } else if self.sess.check_name(attr, sym::proc_macro) {
+            self.collect_bang_proc_macro(item);
+        };
+
+        let prev_in_root = mem::replace(&mut self.in_root, false);
+        visit::walk_item(self, item);
+        self.in_root = prev_in_root;
+    }
+
+    fn visit_mac(&mut self, mac: &'a ast::MacCall) {
+        visit::walk_mac(self, mac)
+    }
+}
+
+// Creates a new module which looks like:
+//
+//      const _: () = {
+//          extern crate proc_macro;
+//
+//          use proc_macro::bridge::client::ProcMacro;
+//
+//          #[rustc_proc_macro_decls]
+//          #[allow(deprecated)]
+//          static DECLS: &[ProcMacro] = &[
+//              ProcMacro::custom_derive($name_trait1, &[], ::$name1);
+//              ProcMacro::custom_derive($name_trait2, &["attribute_name"], ::$name2);
+//              // ...
+//          ];
+//      }
+fn mk_decls(
+    ast_krate: &mut ast::Crate,
+    cx: &mut ExtCtxt<'_>,
+    macros: &[ProcMacro],
+) -> P<ast::Item> {
+    // We're the ones filling in this Vec,
+    // so it should be empty to start with
+    assert!(ast_krate.proc_macros.is_empty());
+
+    let expn_id = cx.resolver.expansion_for_ast_pass(
+        DUMMY_SP,
+        AstPass::ProcMacroHarness,
+        &[sym::rustc_attrs, sym::proc_macro_internals],
+        None,
+    );
+    let span = DUMMY_SP.with_def_site_ctxt(expn_id);
+
+    let proc_macro = Ident::new(sym::proc_macro, span);
+    let krate = cx.item(span, proc_macro, Vec::new(), ast::ItemKind::ExternCrate(None));
+
+    let bridge = Ident::new(sym::bridge, span);
+    let client = Ident::new(sym::client, span);
+    let proc_macro_ty = Ident::new(sym::ProcMacro, span);
+    let custom_derive = Ident::new(sym::custom_derive, span);
+    let attr = Ident::new(sym::attr, span);
+    let bang = Ident::new(sym::bang, span);
+
+    let krate_ref = RefCell::new(ast_krate);
+
+    // We add NodeIds to 'krate.proc_macros' in the order
+    // that we generate expressions. The position of each NodeId
+    // in the 'proc_macros' Vec corresponds to its position
+    // in the static array that will be generated
+    let decls = {
+        let local_path =
+            |sp: Span, name| cx.expr_path(cx.path(sp.with_ctxt(span.ctxt()), vec![name]));
+        let proc_macro_ty_method_path = |method| {
+            cx.expr_path(cx.path(span, vec![proc_macro, bridge, client, proc_macro_ty, method]))
+        };
+        macros
+            .iter()
+            .map(|m| match m {
+                ProcMacro::Derive(cd) => {
+                    krate_ref.borrow_mut().proc_macros.push(cd.id);
+                    cx.expr_call(
+                        span,
+                        proc_macro_ty_method_path(custom_derive),
+                        vec![
+                            cx.expr_str(cd.span, cd.trait_name),
+                            cx.expr_vec_slice(
+                                span,
+                                cd.attrs
+                                    .iter()
+                                    .map(|&s| cx.expr_str(cd.span, s))
+                                    .collect::<Vec<_>>(),
+                            ),
+                            local_path(cd.span, cd.function_name),
+                        ],
+                    )
+                }
+                ProcMacro::Def(ca) => {
+                    krate_ref.borrow_mut().proc_macros.push(ca.id);
+                    let ident = match ca.def_type {
+                        ProcMacroDefType::Attr => attr,
+                        ProcMacroDefType::Bang => bang,
+                    };
+
+                    cx.expr_call(
+                        span,
+                        proc_macro_ty_method_path(ident),
+                        vec![
+                            cx.expr_str(ca.span, ca.function_name.name),
+                            local_path(ca.span, ca.function_name),
+                        ],
+                    )
+                }
+            })
+            .collect()
+    };
+
+    let decls_static = cx
+        .item_static(
+            span,
+            Ident::new(sym::_DECLS, span),
+            cx.ty_rptr(
+                span,
+                cx.ty(
+                    span,
+                    ast::TyKind::Slice(
+                        cx.ty_path(cx.path(span, vec![proc_macro, bridge, client, proc_macro_ty])),
+                    ),
+                ),
+                None,
+                ast::Mutability::Not,
+            ),
+            ast::Mutability::Not,
+            cx.expr_vec_slice(span, decls),
+        )
+        .map(|mut i| {
+            let attr = cx.meta_word(span, sym::rustc_proc_macro_decls);
+            i.attrs.push(cx.attribute(attr));
+
+            let deprecated_attr = attr::mk_nested_word_item(Ident::new(sym::deprecated, span));
+            let allow_deprecated_attr =
+                attr::mk_list_item(Ident::new(sym::allow, span), vec![deprecated_attr]);
+            i.attrs.push(cx.attribute(allow_deprecated_attr));
+
+            i
+        });
+
+    let block = cx.expr_block(
+        cx.block(span, vec![cx.stmt_item(span, krate), cx.stmt_item(span, decls_static)]),
+    );
+
+    let anon_constant = cx.item_const(
+        span,
+        Ident::new(kw::Underscore, span),
+        cx.ty(span, ast::TyKind::Tup(Vec::new())),
+        block,
+    );
+
+    // Integrate the new item into existing module structures.
+    let items = AstFragment::Items(smallvec![anon_constant]);
+    cx.monotonic_expander().fully_expand_fragment(items).make_items().pop().unwrap()
+}
diff --git a/compiler/rustc_builtin_macros/src/source_util.rs b/compiler/rustc_builtin_macros/src/source_util.rs
new file mode 100644
index 00000000000..70753208af3
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/source_util.rs
@@ -0,0 +1,225 @@
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_ast_pretty::pprust;
+use rustc_expand::base::{self, *};
+use rustc_expand::module::DirectoryOwnership;
+use rustc_parse::{self, new_parser_from_file, parser::Parser};
+use rustc_session::lint::builtin::INCOMPLETE_INCLUDE;
+use rustc_span::symbol::Symbol;
+use rustc_span::{self, Pos, Span};
+
+use smallvec::SmallVec;
+use std::rc::Rc;
+
+use rustc_data_structures::sync::Lrc;
+
+// These macros all relate to the file system; they either return
+// the column/row/filename of the expression, or they include
+// a given file into the current one.
+
+/// line!(): expands to the current line number
+pub fn expand_line(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    base::check_zero_tts(cx, sp, tts, "line!");
+
+    let topmost = cx.expansion_cause().unwrap_or(sp);
+    let loc = cx.source_map().lookup_char_pos(topmost.lo());
+
+    base::MacEager::expr(cx.expr_u32(topmost, loc.line as u32))
+}
+
+/* column!(): expands to the current column number */
+pub fn expand_column(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    base::check_zero_tts(cx, sp, tts, "column!");
+
+    let topmost = cx.expansion_cause().unwrap_or(sp);
+    let loc = cx.source_map().lookup_char_pos(topmost.lo());
+
+    base::MacEager::expr(cx.expr_u32(topmost, loc.col.to_usize() as u32 + 1))
+}
+
+/// file!(): expands to the current filename */
+/// The source_file (`loc.file`) contains a bunch more information we could spit
+/// out if we wanted.
+pub fn expand_file(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    base::check_zero_tts(cx, sp, tts, "file!");
+
+    let topmost = cx.expansion_cause().unwrap_or(sp);
+    let loc = cx.source_map().lookup_char_pos(topmost.lo());
+    base::MacEager::expr(cx.expr_str(topmost, Symbol::intern(&loc.file.name.to_string())))
+}
+
+pub fn expand_stringify(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    let s = pprust::tts_to_string(&tts);
+    base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&s)))
+}
+
+pub fn expand_mod(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    base::check_zero_tts(cx, sp, tts, "module_path!");
+    let mod_path = &cx.current_expansion.module.mod_path;
+    let string = mod_path.iter().map(|x| x.to_string()).collect::<Vec<String>>().join("::");
+
+    base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&string)))
+}
+
+/// include! : parse the given file as an expr
+/// This is generally a bad idea because it's going to behave
+/// unhygienically.
+pub fn expand_include<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'cx> {
+    let sp = cx.with_def_site_ctxt(sp);
+    let file = match get_single_str_from_tts(cx, sp, tts, "include!") {
+        Some(f) => f,
+        None => return DummyResult::any(sp),
+    };
+    // The file will be added to the code map by the parser
+    let mut file = match cx.resolve_path(file, sp) {
+        Ok(f) => f,
+        Err(mut err) => {
+            err.emit();
+            return DummyResult::any(sp);
+        }
+    };
+    let p = new_parser_from_file(cx.parse_sess(), &file, Some(sp));
+
+    // If in the included file we have e.g., `mod bar;`,
+    // then the path of `bar.rs` should be relative to the directory of `file`.
+    // See https://github.com/rust-lang/rust/pull/69838/files#r395217057 for a discussion.
+    // `MacroExpander::fully_expand_fragment` later restores, so "stack discipline" is maintained.
+    file.pop();
+    cx.current_expansion.directory_ownership = DirectoryOwnership::Owned { relative: None };
+    let mod_path = cx.current_expansion.module.mod_path.clone();
+    cx.current_expansion.module = Rc::new(ModuleData { mod_path, directory: file });
+
+    struct ExpandResult<'a> {
+        p: Parser<'a>,
+        node_id: ast::NodeId,
+    }
+    impl<'a> base::MacResult for ExpandResult<'a> {
+        fn make_expr(mut self: Box<ExpandResult<'a>>) -> Option<P<ast::Expr>> {
+            let r = base::parse_expr(&mut self.p)?;
+            if self.p.token != token::Eof {
+                self.p.sess.buffer_lint(
+                    &INCOMPLETE_INCLUDE,
+                    self.p.token.span,
+                    self.node_id,
+                    "include macro expected single expression in source",
+                );
+            }
+            Some(r)
+        }
+
+        fn make_items(mut self: Box<ExpandResult<'a>>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
+            let mut ret = SmallVec::new();
+            while self.p.token != token::Eof {
+                match self.p.parse_item() {
+                    Err(mut err) => {
+                        err.emit();
+                        break;
+                    }
+                    Ok(Some(item)) => ret.push(item),
+                    Ok(None) => {
+                        let token = pprust::token_to_string(&self.p.token);
+                        let msg = format!("expected item, found `{}`", token);
+                        self.p.struct_span_err(self.p.token.span, &msg).emit();
+                        break;
+                    }
+                }
+            }
+            Some(ret)
+        }
+    }
+
+    Box::new(ExpandResult { p, node_id: cx.resolver.lint_node_id(cx.current_expansion.id) })
+}
+
+// include_str! : read the given file, insert it as a literal string expr
+pub fn expand_include_str(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    let file = match get_single_str_from_tts(cx, sp, tts, "include_str!") {
+        Some(f) => f,
+        None => return DummyResult::any(sp),
+    };
+    let file = match cx.resolve_path(file, sp) {
+        Ok(f) => f,
+        Err(mut err) => {
+            err.emit();
+            return DummyResult::any(sp);
+        }
+    };
+    match cx.source_map().load_binary_file(&file) {
+        Ok(bytes) => match std::str::from_utf8(&bytes) {
+            Ok(src) => {
+                let interned_src = Symbol::intern(&src);
+                base::MacEager::expr(cx.expr_str(sp, interned_src))
+            }
+            Err(_) => {
+                cx.span_err(sp, &format!("{} wasn't a utf-8 file", file.display()));
+                DummyResult::any(sp)
+            }
+        },
+        Err(e) => {
+            cx.span_err(sp, &format!("couldn't read {}: {}", file.display(), e));
+            DummyResult::any(sp)
+        }
+    }
+}
+
+pub fn expand_include_bytes(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let sp = cx.with_def_site_ctxt(sp);
+    let file = match get_single_str_from_tts(cx, sp, tts, "include_bytes!") {
+        Some(f) => f,
+        None => return DummyResult::any(sp),
+    };
+    let file = match cx.resolve_path(file, sp) {
+        Ok(f) => f,
+        Err(mut err) => {
+            err.emit();
+            return DummyResult::any(sp);
+        }
+    };
+    match cx.source_map().load_binary_file(&file) {
+        Ok(bytes) => base::MacEager::expr(cx.expr_lit(sp, ast::LitKind::ByteStr(Lrc::new(bytes)))),
+        Err(e) => {
+            cx.span_err(sp, &format!("couldn't read {}: {}", file.display(), e));
+            DummyResult::any(sp)
+        }
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/standard_library_imports.rs b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
new file mode 100644
index 00000000000..e801b5c7b0c
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
@@ -0,0 +1,85 @@
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_expand::base::{ExtCtxt, ResolverExpand};
+use rustc_expand::expand::ExpansionConfig;
+use rustc_session::Session;
+use rustc_span::edition::Edition;
+use rustc_span::hygiene::AstPass;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::DUMMY_SP;
+
+pub fn inject(
+    mut krate: ast::Crate,
+    resolver: &mut dyn ResolverExpand,
+    sess: &Session,
+    alt_std_name: Option<Symbol>,
+) -> (ast::Crate, Option<Symbol>) {
+    let rust_2018 = sess.parse_sess.edition >= Edition::Edition2018;
+
+    // the first name in this list is the crate name of the crate with the prelude
+    let names: &[Symbol] = if sess.contains_name(&krate.attrs, sym::no_core) {
+        return (krate, None);
+    } else if sess.contains_name(&krate.attrs, sym::no_std) {
+        if sess.contains_name(&krate.attrs, sym::compiler_builtins) {
+            &[sym::core]
+        } else {
+            &[sym::core, sym::compiler_builtins]
+        }
+    } else {
+        &[sym::std]
+    };
+
+    let expn_id = resolver.expansion_for_ast_pass(
+        DUMMY_SP,
+        AstPass::StdImports,
+        &[sym::prelude_import],
+        None,
+    );
+    let span = DUMMY_SP.with_def_site_ctxt(expn_id);
+    let call_site = DUMMY_SP.with_call_site_ctxt(expn_id);
+
+    let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
+    let cx = ExtCtxt::new(sess, ecfg, resolver, None);
+
+    // .rev() to preserve ordering above in combination with insert(0, ...)
+    for &name in names.iter().rev() {
+        let ident = if rust_2018 { Ident::new(name, span) } else { Ident::new(name, call_site) };
+        krate.module.items.insert(
+            0,
+            cx.item(
+                span,
+                ident,
+                vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
+                ast::ItemKind::ExternCrate(alt_std_name),
+            ),
+        );
+    }
+
+    // The crates have been injected, the assumption is that the first one is
+    // the one with the prelude.
+    let name = names[0];
+
+    let import_path = if rust_2018 {
+        [name, sym::prelude, sym::v1].iter().map(|symbol| Ident::new(*symbol, span)).collect()
+    } else {
+        [kw::PathRoot, name, sym::prelude, sym::v1]
+            .iter()
+            .map(|symbol| Ident::new(*symbol, span))
+            .collect()
+    };
+
+    let use_item = cx.item(
+        span,
+        Ident::invalid(),
+        vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
+        ast::ItemKind::Use(P(ast::UseTree {
+            prefix: cx.path(span, import_path),
+            kind: ast::UseTreeKind::Glob,
+            span,
+        })),
+    );
+
+    krate.module.items.insert(0, use_item);
+
+    (krate, Some(name))
+}
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
new file mode 100644
index 00000000000..8e56e80bba2
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -0,0 +1,471 @@
+/// The expansion from a test function to the appropriate test struct for libtest
+/// Ideally, this code would be in libtest but for efficiency and error messages it lives here.
+use crate::util::check_builtin_macro_attribute;
+
+use rustc_ast as ast;
+use rustc_ast::attr;
+use rustc_ast_pretty::pprust;
+use rustc_expand::base::*;
+use rustc_session::Session;
+use rustc_span::source_map::respan;
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::Span;
+
+use std::iter;
+
+// #[test_case] is used by custom test authors to mark tests
+// When building for test, it needs to make the item public and gensym the name
+// Otherwise, we'll omit the item. This behavior means that any item annotated
+// with #[test_case] is never addressable.
+//
+// We mark item with an inert attribute "rustc_test_marker" which the test generation
+// logic will pick up on.
+pub fn expand_test_case(
+    ecx: &mut ExtCtxt<'_>,
+    attr_sp: Span,
+    meta_item: &ast::MetaItem,
+    anno_item: Annotatable,
+) -> Vec<Annotatable> {
+    check_builtin_macro_attribute(ecx, meta_item, sym::test_case);
+
+    if !ecx.ecfg.should_test {
+        return vec![];
+    }
+
+    let sp = ecx.with_def_site_ctxt(attr_sp);
+    let mut item = anno_item.expect_item();
+    item = item.map(|mut item| {
+        item.vis = respan(item.vis.span, ast::VisibilityKind::Public);
+        item.ident.span = item.ident.span.with_ctxt(sp.ctxt());
+        item.attrs.push(ecx.attribute(ecx.meta_word(sp, sym::rustc_test_marker)));
+        item
+    });
+
+    return vec![Annotatable::Item(item)];
+}
+
+pub fn expand_test(
+    cx: &mut ExtCtxt<'_>,
+    attr_sp: Span,
+    meta_item: &ast::MetaItem,
+    item: Annotatable,
+) -> Vec<Annotatable> {
+    check_builtin_macro_attribute(cx, meta_item, sym::test);
+    expand_test_or_bench(cx, attr_sp, item, false)
+}
+
+pub fn expand_bench(
+    cx: &mut ExtCtxt<'_>,
+    attr_sp: Span,
+    meta_item: &ast::MetaItem,
+    item: Annotatable,
+) -> Vec<Annotatable> {
+    check_builtin_macro_attribute(cx, meta_item, sym::bench);
+    expand_test_or_bench(cx, attr_sp, item, true)
+}
+
+pub fn expand_test_or_bench(
+    cx: &mut ExtCtxt<'_>,
+    attr_sp: Span,
+    item: Annotatable,
+    is_bench: bool,
+) -> Vec<Annotatable> {
+    // If we're not in test configuration, remove the annotated item
+    if !cx.ecfg.should_test {
+        return vec![];
+    }
+
+    let item = match item {
+        Annotatable::Item(i) => i,
+        other => {
+            cx.struct_span_err(
+                other.span(),
+                "`#[test]` attribute is only allowed on non associated functions",
+            )
+            .emit();
+            return vec![other];
+        }
+    };
+
+    if let ast::ItemKind::MacCall(_) = item.kind {
+        cx.sess.parse_sess.span_diagnostic.span_warn(
+            item.span,
+            "`#[test]` attribute should not be used on macros. Use `#[cfg(test)]` instead.",
+        );
+        return vec![Annotatable::Item(item)];
+    }
+
+    // has_*_signature will report any errors in the type so compilation
+    // will fail. We shouldn't try to expand in this case because the errors
+    // would be spurious.
+    if (!is_bench && !has_test_signature(cx, &item))
+        || (is_bench && !has_bench_signature(cx, &item))
+    {
+        return vec![Annotatable::Item(item)];
+    }
+
+    let (sp, attr_sp) = (cx.with_def_site_ctxt(item.span), cx.with_def_site_ctxt(attr_sp));
+
+    let test_id = Ident::new(sym::test, attr_sp);
+
+    // creates test::$name
+    let test_path = |name| cx.path(sp, vec![test_id, Ident::from_str_and_span(name, sp)]);
+
+    // creates test::ShouldPanic::$name
+    let should_panic_path = |name| {
+        cx.path(
+            sp,
+            vec![
+                test_id,
+                Ident::from_str_and_span("ShouldPanic", sp),
+                Ident::from_str_and_span(name, sp),
+            ],
+        )
+    };
+
+    // creates test::TestType::$name
+    let test_type_path = |name| {
+        cx.path(
+            sp,
+            vec![
+                test_id,
+                Ident::from_str_and_span("TestType", sp),
+                Ident::from_str_and_span(name, sp),
+            ],
+        )
+    };
+
+    // creates $name: $expr
+    let field = |name, expr| cx.field_imm(sp, Ident::from_str_and_span(name, sp), expr);
+
+    let test_fn = if is_bench {
+        // A simple ident for a lambda
+        let b = Ident::from_str_and_span("b", attr_sp);
+
+        cx.expr_call(
+            sp,
+            cx.expr_path(test_path("StaticBenchFn")),
+            vec![
+                // |b| self::test::assert_test_result(
+                cx.lambda1(
+                    sp,
+                    cx.expr_call(
+                        sp,
+                        cx.expr_path(test_path("assert_test_result")),
+                        vec![
+                            // super::$test_fn(b)
+                            cx.expr_call(
+                                sp,
+                                cx.expr_path(cx.path(sp, vec![item.ident])),
+                                vec![cx.expr_ident(sp, b)],
+                            ),
+                        ],
+                    ),
+                    b,
+                ), // )
+            ],
+        )
+    } else {
+        cx.expr_call(
+            sp,
+            cx.expr_path(test_path("StaticTestFn")),
+            vec![
+                // || {
+                cx.lambda0(
+                    sp,
+                    // test::assert_test_result(
+                    cx.expr_call(
+                        sp,
+                        cx.expr_path(test_path("assert_test_result")),
+                        vec![
+                            // $test_fn()
+                            cx.expr_call(sp, cx.expr_path(cx.path(sp, vec![item.ident])), vec![]), // )
+                        ],
+                    ), // }
+                ), // )
+            ],
+        )
+    };
+
+    let mut test_const = cx.item(
+        sp,
+        Ident::new(item.ident.name, sp),
+        vec![
+            // #[cfg(test)]
+            cx.attribute(attr::mk_list_item(
+                Ident::new(sym::cfg, attr_sp),
+                vec![attr::mk_nested_word_item(Ident::new(sym::test, attr_sp))],
+            )),
+            // #[rustc_test_marker]
+            cx.attribute(cx.meta_word(attr_sp, sym::rustc_test_marker)),
+        ],
+        // const $ident: test::TestDescAndFn =
+        ast::ItemKind::Const(
+            ast::Defaultness::Final,
+            cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
+            // test::TestDescAndFn {
+            Some(
+                cx.expr_struct(
+                    sp,
+                    test_path("TestDescAndFn"),
+                    vec![
+                        // desc: test::TestDesc {
+                        field(
+                            "desc",
+                            cx.expr_struct(
+                                sp,
+                                test_path("TestDesc"),
+                                vec![
+                                    // name: "path::to::test"
+                                    field(
+                                        "name",
+                                        cx.expr_call(
+                                            sp,
+                                            cx.expr_path(test_path("StaticTestName")),
+                                            vec![cx.expr_str(
+                                                sp,
+                                                Symbol::intern(&item_path(
+                                                    // skip the name of the root module
+                                                    &cx.current_expansion.module.mod_path[1..],
+                                                    &item.ident,
+                                                )),
+                                            )],
+                                        ),
+                                    ),
+                                    // ignore: true | false
+                                    field(
+                                        "ignore",
+                                        cx.expr_bool(sp, should_ignore(&cx.sess, &item)),
+                                    ),
+                                    // allow_fail: true | false
+                                    field(
+                                        "allow_fail",
+                                        cx.expr_bool(sp, should_fail(&cx.sess, &item)),
+                                    ),
+                                    // should_panic: ...
+                                    field(
+                                        "should_panic",
+                                        match should_panic(cx, &item) {
+                                            // test::ShouldPanic::No
+                                            ShouldPanic::No => {
+                                                cx.expr_path(should_panic_path("No"))
+                                            }
+                                            // test::ShouldPanic::Yes
+                                            ShouldPanic::Yes(None) => {
+                                                cx.expr_path(should_panic_path("Yes"))
+                                            }
+                                            // test::ShouldPanic::YesWithMessage("...")
+                                            ShouldPanic::Yes(Some(sym)) => cx.expr_call(
+                                                sp,
+                                                cx.expr_path(should_panic_path("YesWithMessage")),
+                                                vec![cx.expr_str(sp, sym)],
+                                            ),
+                                        },
+                                    ),
+                                    // test_type: ...
+                                    field(
+                                        "test_type",
+                                        match test_type(cx) {
+                                            // test::TestType::UnitTest
+                                            TestType::UnitTest => {
+                                                cx.expr_path(test_type_path("UnitTest"))
+                                            }
+                                            // test::TestType::IntegrationTest
+                                            TestType::IntegrationTest => {
+                                                cx.expr_path(test_type_path("IntegrationTest"))
+                                            }
+                                            // test::TestPath::Unknown
+                                            TestType::Unknown => {
+                                                cx.expr_path(test_type_path("Unknown"))
+                                            }
+                                        },
+                                    ),
+                                    // },
+                                ],
+                            ),
+                        ),
+                        // testfn: test::StaticTestFn(...) | test::StaticBenchFn(...)
+                        field("testfn", test_fn), // }
+                    ],
+                ), // }
+            ),
+        ),
+    );
+    test_const = test_const.map(|mut tc| {
+        tc.vis.node = ast::VisibilityKind::Public;
+        tc
+    });
+
+    // extern crate test
+    let test_extern = cx.item(sp, test_id, vec![], ast::ItemKind::ExternCrate(None));
+
+    tracing::debug!("synthetic test item:\n{}\n", pprust::item_to_string(&test_const));
+
+    vec![
+        // Access to libtest under a hygienic name
+        Annotatable::Item(test_extern),
+        // The generated test case
+        Annotatable::Item(test_const),
+        // The original item
+        Annotatable::Item(item),
+    ]
+}
+
+fn item_path(mod_path: &[Ident], item_ident: &Ident) -> String {
+    mod_path
+        .iter()
+        .chain(iter::once(item_ident))
+        .map(|x| x.to_string())
+        .collect::<Vec<String>>()
+        .join("::")
+}
+
+enum ShouldPanic {
+    No,
+    Yes(Option<Symbol>),
+}
+
+fn should_ignore(sess: &Session, i: &ast::Item) -> bool {
+    sess.contains_name(&i.attrs, sym::ignore)
+}
+
+fn should_fail(sess: &Session, i: &ast::Item) -> bool {
+    sess.contains_name(&i.attrs, sym::allow_fail)
+}
+
+fn should_panic(cx: &ExtCtxt<'_>, i: &ast::Item) -> ShouldPanic {
+    match cx.sess.find_by_name(&i.attrs, sym::should_panic) {
+        Some(attr) => {
+            let sd = &cx.sess.parse_sess.span_diagnostic;
+
+            match attr.meta_item_list() {
+                // Handle #[should_panic(expected = "foo")]
+                Some(list) => {
+                    let msg = list
+                        .iter()
+                        .find(|mi| mi.has_name(sym::expected))
+                        .and_then(|mi| mi.meta_item())
+                        .and_then(|mi| mi.value_str());
+                    if list.len() != 1 || msg.is_none() {
+                        sd.struct_span_warn(
+                            attr.span,
+                            "argument must be of the form: \
+                             `expected = \"error message\"`",
+                        )
+                        .note(
+                            "errors in this attribute were erroneously \
+                                allowed and will become a hard error in a \
+                                future release.",
+                        )
+                        .emit();
+                        ShouldPanic::Yes(None)
+                    } else {
+                        ShouldPanic::Yes(msg)
+                    }
+                }
+                // Handle #[should_panic] and #[should_panic = "expected"]
+                None => ShouldPanic::Yes(attr.value_str()),
+            }
+        }
+        None => ShouldPanic::No,
+    }
+}
+
+enum TestType {
+    UnitTest,
+    IntegrationTest,
+    Unknown,
+}
+
+/// Attempts to determine the type of test.
+/// Since doctests are created without macro expanding, only possible variants here
+/// are `UnitTest`, `IntegrationTest` or `Unknown`.
+fn test_type(cx: &ExtCtxt<'_>) -> TestType {
+    // Root path from context contains the topmost sources directory of the crate.
+    // I.e., for `project` with sources in `src` and tests in `tests` folders
+    // (no matter how many nested folders lie inside),
+    // there will be two different root paths: `/project/src` and `/project/tests`.
+    let crate_path = cx.root_path.as_path();
+
+    if crate_path.ends_with("src") {
+        // `/src` folder contains unit-tests.
+        TestType::UnitTest
+    } else if crate_path.ends_with("tests") {
+        // `/tests` folder contains integration tests.
+        TestType::IntegrationTest
+    } else {
+        // Crate layout doesn't match expected one, test type is unknown.
+        TestType::Unknown
+    }
+}
+
+fn has_test_signature(cx: &ExtCtxt<'_>, i: &ast::Item) -> bool {
+    let has_should_panic_attr = cx.sess.contains_name(&i.attrs, sym::should_panic);
+    let sd = &cx.sess.parse_sess.span_diagnostic;
+    if let ast::ItemKind::Fn(_, ref sig, ref generics, _) = i.kind {
+        if let ast::Unsafe::Yes(span) = sig.header.unsafety {
+            sd.struct_span_err(i.span, "unsafe functions cannot be used for tests")
+                .span_label(span, "`unsafe` because of this")
+                .emit();
+            return false;
+        }
+        if let ast::Async::Yes { span, .. } = sig.header.asyncness {
+            sd.struct_span_err(i.span, "async functions cannot be used for tests")
+                .span_label(span, "`async` because of this")
+                .emit();
+            return false;
+        }
+
+        // If the termination trait is active, the compiler will check that the output
+        // type implements the `Termination` trait as `libtest` enforces that.
+        let has_output = match sig.decl.output {
+            ast::FnRetTy::Default(..) => false,
+            ast::FnRetTy::Ty(ref t) if t.kind.is_unit() => false,
+            _ => true,
+        };
+
+        if !sig.decl.inputs.is_empty() {
+            sd.span_err(i.span, "functions used as tests can not have any arguments");
+            return false;
+        }
+
+        match (has_output, has_should_panic_attr) {
+            (true, true) => {
+                sd.span_err(i.span, "functions using `#[should_panic]` must return `()`");
+                false
+            }
+            (true, false) => {
+                if !generics.params.is_empty() {
+                    sd.span_err(i.span, "functions used as tests must have signature fn() -> ()");
+                    false
+                } else {
+                    true
+                }
+            }
+            (false, _) => true,
+        }
+    } else {
+        sd.span_err(i.span, "only functions may be used as tests");
+        false
+    }
+}
+
+fn has_bench_signature(cx: &ExtCtxt<'_>, i: &ast::Item) -> bool {
+    let has_sig = if let ast::ItemKind::Fn(_, ref sig, _, _) = i.kind {
+        // N.B., inadequate check, but we're running
+        // well before resolve, can't get too deep.
+        sig.decl.inputs.len() == 1
+    } else {
+        false
+    };
+
+    if !has_sig {
+        cx.sess.parse_sess.span_diagnostic.span_err(
+            i.span,
+            "functions used as benches must have \
+            signature `fn(&mut Bencher) -> impl Termination`",
+        );
+    }
+
+    has_sig
+}
diff --git a/compiler/rustc_builtin_macros/src/test_harness.rs b/compiler/rustc_builtin_macros/src/test_harness.rs
new file mode 100644
index 00000000000..0ea60665d67
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/test_harness.rs
@@ -0,0 +1,383 @@
+// Code that generates a test runner to run all the tests in a crate
+
+use rustc_ast as ast;
+use rustc_ast::attr;
+use rustc_ast::entry::EntryPointType;
+use rustc_ast::mut_visit::{ExpectOne, *};
+use rustc_ast::ptr::P;
+use rustc_expand::base::{ExtCtxt, ResolverExpand};
+use rustc_expand::expand::{AstFragment, ExpansionConfig};
+use rustc_feature::Features;
+use rustc_session::Session;
+use rustc_span::hygiene::{AstPass, SyntaxContext, Transparency};
+use rustc_span::source_map::respan;
+use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+use rustc_target::spec::PanicStrategy;
+use smallvec::{smallvec, SmallVec};
+use tracing::debug;
+
+use std::{iter, mem};
+
+struct Test {
+    span: Span,
+    ident: Ident,
+}
+
+struct TestCtxt<'a> {
+    ext_cx: ExtCtxt<'a>,
+    panic_strategy: PanicStrategy,
+    def_site: Span,
+    test_cases: Vec<Test>,
+    reexport_test_harness_main: Option<Symbol>,
+    test_runner: Option<ast::Path>,
+}
+
+// Traverse the crate, collecting all the test functions, eliding any
+// existing main functions, and synthesizing a main test harness
+pub fn inject(sess: &Session, resolver: &mut dyn ResolverExpand, krate: &mut ast::Crate) {
+    let span_diagnostic = sess.diagnostic();
+    let panic_strategy = sess.panic_strategy();
+    let platform_panic_strategy = sess.target.target.options.panic_strategy;
+
+    // Check for #![reexport_test_harness_main = "some_name"] which gives the
+    // main test function the name `some_name` without hygiene. This needs to be
+    // unconditional, so that the attribute is still marked as used in
+    // non-test builds.
+    let reexport_test_harness_main =
+        sess.first_attr_value_str_by_name(&krate.attrs, sym::reexport_test_harness_main);
+
+    // Do this here so that the test_runner crate attribute gets marked as used
+    // even in non-test builds
+    let test_runner = get_test_runner(sess, span_diagnostic, &krate);
+
+    if sess.opts.test {
+        let panic_strategy = match (panic_strategy, sess.opts.debugging_opts.panic_abort_tests) {
+            (PanicStrategy::Abort, true) => PanicStrategy::Abort,
+            (PanicStrategy::Abort, false) => {
+                if panic_strategy == platform_panic_strategy {
+                    // Silently allow compiling with panic=abort on these platforms,
+                    // but with old behavior (abort if a test fails).
+                } else {
+                    span_diagnostic.err(
+                        "building tests with panic=abort is not supported \
+                                         without `-Zpanic_abort_tests`",
+                    );
+                }
+                PanicStrategy::Unwind
+            }
+            (PanicStrategy::Unwind, _) => PanicStrategy::Unwind,
+        };
+        generate_test_harness(
+            sess,
+            resolver,
+            reexport_test_harness_main,
+            krate,
+            &sess.features_untracked(),
+            panic_strategy,
+            test_runner,
+        )
+    }
+}
+
+struct TestHarnessGenerator<'a> {
+    cx: TestCtxt<'a>,
+    tests: Vec<Test>,
+}
+
+impl<'a> MutVisitor for TestHarnessGenerator<'a> {
+    fn visit_crate(&mut self, c: &mut ast::Crate) {
+        noop_visit_crate(c, self);
+
+        // Create a main function to run our tests
+        c.module.items.push(mk_main(&mut self.cx));
+    }
+
+    fn flat_map_item(&mut self, i: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
+        let mut item = i.into_inner();
+        if is_test_case(&self.cx.ext_cx.sess, &item) {
+            debug!("this is a test item");
+
+            let test = Test { span: item.span, ident: item.ident };
+            self.tests.push(test);
+        }
+
+        // We don't want to recurse into anything other than mods, since
+        // mods or tests inside of functions will break things
+        if let ast::ItemKind::Mod(mut module) = item.kind {
+            let tests = mem::take(&mut self.tests);
+            noop_visit_mod(&mut module, self);
+            let mut tests = mem::replace(&mut self.tests, tests);
+
+            if !tests.is_empty() {
+                let parent =
+                    if item.id == ast::DUMMY_NODE_ID { ast::CRATE_NODE_ID } else { item.id };
+                // Create an identifier that will hygienically resolve the test
+                // case name, even in another module.
+                let expn_id = self.cx.ext_cx.resolver.expansion_for_ast_pass(
+                    module.inner,
+                    AstPass::TestHarness,
+                    &[],
+                    Some(parent),
+                );
+                for test in &mut tests {
+                    // See the comment on `mk_main` for why we're using
+                    // `apply_mark` directly.
+                    test.ident.span = test.ident.span.apply_mark(expn_id, Transparency::Opaque);
+                }
+                self.cx.test_cases.extend(tests);
+            }
+            item.kind = ast::ItemKind::Mod(module);
+        }
+        smallvec![P(item)]
+    }
+
+    fn visit_mac(&mut self, _mac: &mut ast::MacCall) {
+        // Do nothing.
+    }
+}
+
+// Beware, this is duplicated in librustc_passes/entry.rs (with
+// `rustc_hir::Item`), so make sure to keep them in sync.
+fn entry_point_type(sess: &Session, item: &ast::Item, depth: usize) -> EntryPointType {
+    match item.kind {
+        ast::ItemKind::Fn(..) => {
+            if sess.contains_name(&item.attrs, sym::start) {
+                EntryPointType::Start
+            } else if sess.contains_name(&item.attrs, sym::main) {
+                EntryPointType::MainAttr
+            } else if item.ident.name == sym::main {
+                if depth == 1 {
+                    // This is a top-level function so can be 'main'
+                    EntryPointType::MainNamed
+                } else {
+                    EntryPointType::OtherMain
+                }
+            } else {
+                EntryPointType::None
+            }
+        }
+        _ => EntryPointType::None,
+    }
+}
+/// A folder used to remove any entry points (like fn main) because the harness
+/// generator will provide its own
+struct EntryPointCleaner<'a> {
+    // Current depth in the ast
+    sess: &'a Session,
+    depth: usize,
+    def_site: Span,
+}
+
+impl<'a> MutVisitor for EntryPointCleaner<'a> {
+    fn flat_map_item(&mut self, i: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
+        self.depth += 1;
+        let item = noop_flat_map_item(i, self).expect_one("noop did something");
+        self.depth -= 1;
+
+        // Remove any #[main] or #[start] from the AST so it doesn't
+        // clash with the one we're going to add, but mark it as
+        // #[allow(dead_code)] to avoid printing warnings.
+        let item = match entry_point_type(self.sess, &item, self.depth) {
+            EntryPointType::MainNamed | EntryPointType::MainAttr | EntryPointType::Start => item
+                .map(|ast::Item { id, ident, attrs, kind, vis, span, tokens }| {
+                    let allow_ident = Ident::new(sym::allow, self.def_site);
+                    let dc_nested =
+                        attr::mk_nested_word_item(Ident::new(sym::dead_code, self.def_site));
+                    let allow_dead_code_item = attr::mk_list_item(allow_ident, vec![dc_nested]);
+                    let allow_dead_code = attr::mk_attr_outer(allow_dead_code_item);
+                    let attrs = attrs
+                        .into_iter()
+                        .filter(|attr| {
+                            !self.sess.check_name(attr, sym::main)
+                                && !self.sess.check_name(attr, sym::start)
+                        })
+                        .chain(iter::once(allow_dead_code))
+                        .collect();
+
+                    ast::Item { id, ident, attrs, kind, vis, span, tokens }
+                }),
+            EntryPointType::None | EntryPointType::OtherMain => item,
+        };
+
+        smallvec![item]
+    }
+
+    fn visit_mac(&mut self, _mac: &mut ast::MacCall) {
+        // Do nothing.
+    }
+}
+
+/// Crawl over the crate, inserting test reexports and the test main function
+fn generate_test_harness(
+    sess: &Session,
+    resolver: &mut dyn ResolverExpand,
+    reexport_test_harness_main: Option<Symbol>,
+    krate: &mut ast::Crate,
+    features: &Features,
+    panic_strategy: PanicStrategy,
+    test_runner: Option<ast::Path>,
+) {
+    let mut econfig = ExpansionConfig::default("test".to_string());
+    econfig.features = Some(features);
+
+    let ext_cx = ExtCtxt::new(sess, econfig, resolver, None);
+
+    let expn_id = ext_cx.resolver.expansion_for_ast_pass(
+        DUMMY_SP,
+        AstPass::TestHarness,
+        &[sym::main, sym::test, sym::rustc_attrs],
+        None,
+    );
+    let def_site = DUMMY_SP.with_def_site_ctxt(expn_id);
+
+    // Remove the entry points
+    let mut cleaner = EntryPointCleaner { sess, depth: 0, def_site };
+    cleaner.visit_crate(krate);
+
+    let cx = TestCtxt {
+        ext_cx,
+        panic_strategy,
+        def_site,
+        test_cases: Vec::new(),
+        reexport_test_harness_main,
+        test_runner,
+    };
+
+    TestHarnessGenerator { cx, tests: Vec::new() }.visit_crate(krate);
+}
+
+/// Creates a function item for use as the main function of a test build.
+/// This function will call the `test_runner` as specified by the crate attribute
+///
+/// By default this expands to
+///
+/// ```
+/// #[main]
+/// pub fn main() {
+///     extern crate test;
+///     test::test_main_static(&[
+///         &test_const1,
+///         &test_const2,
+///         &test_const3,
+///     ]);
+/// }
+/// ```
+///
+/// Most of the Ident have the usual def-site hygiene for the AST pass. The
+/// exception is the `test_const`s. These have a syntax context that has two
+/// opaque marks: one from the expansion of `test` or `test_case`, and one
+/// generated  in `TestHarnessGenerator::flat_map_item`. When resolving this
+/// identifier after failing to find a matching identifier in the root module
+/// we remove the outer mark, and try resolving at its def-site, which will
+/// then resolve to `test_const`.
+///
+/// The expansion here can be controlled by two attributes:
+///
+/// [`TestCtxt::reexport_test_harness_main`] provides a different name for the `main`
+/// function and [`TestCtxt::test_runner`] provides a path that replaces
+/// `test::test_main_static`.
+fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
+    let sp = cx.def_site;
+    let ecx = &cx.ext_cx;
+    let test_id = Ident::new(sym::test, sp);
+
+    let runner_name = match cx.panic_strategy {
+        PanicStrategy::Unwind => "test_main_static",
+        PanicStrategy::Abort => "test_main_static_abort",
+    };
+
+    // test::test_main_static(...)
+    let mut test_runner = cx
+        .test_runner
+        .clone()
+        .unwrap_or(ecx.path(sp, vec![test_id, Ident::from_str_and_span(runner_name, sp)]));
+
+    test_runner.span = sp;
+
+    let test_main_path_expr = ecx.expr_path(test_runner);
+    let call_test_main = ecx.expr_call(sp, test_main_path_expr, vec![mk_tests_slice(cx, sp)]);
+    let call_test_main = ecx.stmt_expr(call_test_main);
+
+    // extern crate test
+    let test_extern_stmt =
+        ecx.stmt_item(sp, ecx.item(sp, test_id, vec![], ast::ItemKind::ExternCrate(None)));
+
+    // #[main]
+    let main_meta = ecx.meta_word(sp, sym::main);
+    let main_attr = ecx.attribute(main_meta);
+
+    // pub fn main() { ... }
+    let main_ret_ty = ecx.ty(sp, ast::TyKind::Tup(vec![]));
+
+    // If no test runner is provided we need to import the test crate
+    let main_body = if cx.test_runner.is_none() {
+        ecx.block(sp, vec![test_extern_stmt, call_test_main])
+    } else {
+        ecx.block(sp, vec![call_test_main])
+    };
+
+    let decl = ecx.fn_decl(vec![], ast::FnRetTy::Ty(main_ret_ty));
+    let sig = ast::FnSig { decl, header: ast::FnHeader::default(), span: sp };
+    let def = ast::Defaultness::Final;
+    let main = ast::ItemKind::Fn(def, sig, ast::Generics::default(), Some(main_body));
+
+    // Honor the reexport_test_harness_main attribute
+    let main_id = match cx.reexport_test_harness_main {
+        Some(sym) => Ident::new(sym, sp.with_ctxt(SyntaxContext::root())),
+        None => Ident::new(sym::main, sp),
+    };
+
+    let main = P(ast::Item {
+        ident: main_id,
+        attrs: vec![main_attr],
+        id: ast::DUMMY_NODE_ID,
+        kind: main,
+        vis: respan(sp, ast::VisibilityKind::Public),
+        span: sp,
+        tokens: None,
+    });
+
+    // Integrate the new item into existing module structures.
+    let main = AstFragment::Items(smallvec![main]);
+    cx.ext_cx.monotonic_expander().fully_expand_fragment(main).make_items().pop().unwrap()
+}
+
+/// Creates a slice containing every test like so:
+/// &[&test1, &test2]
+fn mk_tests_slice(cx: &TestCtxt<'_>, sp: Span) -> P<ast::Expr> {
+    debug!("building test vector from {} tests", cx.test_cases.len());
+    let ecx = &cx.ext_cx;
+
+    ecx.expr_vec_slice(
+        sp,
+        cx.test_cases
+            .iter()
+            .map(|test| {
+                ecx.expr_addr_of(test.span, ecx.expr_path(ecx.path(test.span, vec![test.ident])))
+            })
+            .collect(),
+    )
+}
+
+fn is_test_case(sess: &Session, i: &ast::Item) -> bool {
+    sess.contains_name(&i.attrs, sym::rustc_test_marker)
+}
+
+fn get_test_runner(
+    sess: &Session,
+    sd: &rustc_errors::Handler,
+    krate: &ast::Crate,
+) -> Option<ast::Path> {
+    let test_attr = sess.find_by_name(&krate.attrs, sym::test_runner)?;
+    let meta_list = test_attr.meta_item_list()?;
+    let span = test_attr.span;
+    match &*meta_list {
+        [single] => match single.meta_item() {
+            Some(meta_item) if meta_item.is_word() => return Some(meta_item.path.clone()),
+            _ => sd.struct_span_err(span, "`test_runner` argument must be a path").emit(),
+        },
+        _ => sd.struct_span_err(span, "`#![test_runner(..)]` accepts exactly 1 argument").emit(),
+    }
+    None
+}
diff --git a/compiler/rustc_builtin_macros/src/trace_macros.rs b/compiler/rustc_builtin_macros/src/trace_macros.rs
new file mode 100644
index 00000000000..c17f2afe494
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/trace_macros.rs
@@ -0,0 +1,29 @@
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_expand::base::{self, ExtCtxt};
+use rustc_span::symbol::kw;
+use rustc_span::Span;
+
+pub fn expand_trace_macros(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tt: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let mut cursor = tt.into_trees();
+    let mut err = false;
+    let value = match &cursor.next() {
+        Some(TokenTree::Token(token)) if token.is_keyword(kw::True) => true,
+        Some(TokenTree::Token(token)) if token.is_keyword(kw::False) => false,
+        _ => {
+            err = true;
+            false
+        }
+    };
+    err |= cursor.next().is_some();
+    if err {
+        cx.span_err(sp, "trace_macros! accepts only `true` or `false`")
+    } else {
+        cx.set_trace_macros(value);
+    }
+
+    base::DummyResult::any_valid(sp)
+}
diff --git a/compiler/rustc_builtin_macros/src/util.rs b/compiler/rustc_builtin_macros/src/util.rs
new file mode 100644
index 00000000000..01ea80c4c8a
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/util.rs
@@ -0,0 +1,12 @@
+use rustc_ast::MetaItem;
+use rustc_expand::base::ExtCtxt;
+use rustc_feature::AttributeTemplate;
+use rustc_parse::validate_attr;
+use rustc_span::Symbol;
+
+pub fn check_builtin_macro_attribute(ecx: &ExtCtxt<'_>, meta_item: &MetaItem, name: Symbol) {
+    // All the built-in macro attributes are "words" at the moment.
+    let template = AttributeTemplate { word: true, ..Default::default() };
+    let attr = ecx.attribute(meta_item.clone());
+    validate_attr::check_builtin_attribute(&ecx.sess.parse_sess, &attr, name, template);
+}