Auto merge of #74862 - mark-i-m:mv-compiler, r=petrochenkov

Move almost all compiler crates to compiler/

This PR implements https://github.com/rust-lang/compiler-team/issues/336 and moves all `rustc_*` crates from `src` to the new `compiler` directory.

`librustc_foo` directories are renamed to `rustc_foo`.
`src` directories are introduced inside `rustc_*` directories to mirror the scheme already use for `library` crates.

1 files changed, 595 insertions, 0 deletions

diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
new file mode 100644
index 00000000000..bc857c97742
--- /dev/null
+++ b/compiler/rustc_parse/src/lib.rs
@@ -0,0 +1,595 @@
+//! The main parser interface.
+
+#![feature(bool_to_option)]
+#![feature(crate_visibility_modifier)]
+#![feature(bindings_after_at)]
+#![feature(try_blocks)]
+#![feature(or_patterns)]
+
+use rustc_ast as ast;
+use rustc_ast::token::{self, DelimToken, Nonterminal, Token, TokenKind};
+use rustc_ast::tokenstream::{self, IsJoint, TokenStream, TokenTree};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::{Diagnostic, FatalError, Level, PResult};
+use rustc_session::parse::ParseSess;
+use rustc_span::{symbol::kw, FileName, SourceFile, Span, DUMMY_SP};
+
+use smallvec::SmallVec;
+use std::mem;
+use std::path::Path;
+use std::str;
+
+use tracing::{debug, info};
+
+pub const MACRO_ARGUMENTS: Option<&'static str> = Some("macro arguments");
+
+#[macro_use]
+pub mod parser;
+use parser::{emit_unclosed_delims, make_unclosed_delims_error, Parser};
+pub mod lexer;
+pub mod validate_attr;
+
+// A bunch of utility functions of the form `parse_<thing>_from_<source>`
+// where <thing> includes crate, expr, item, stmt, tts, and one that
+// uses a HOF to parse anything, and <source> includes file and
+// `source_str`.
+
+/// A variant of 'panictry!' that works on a Vec<Diagnostic> instead of a single DiagnosticBuilder.
+macro_rules! panictry_buffer {
+    ($handler:expr, $e:expr) => {{
+        use rustc_errors::FatalError;
+        use std::result::Result::{Err, Ok};
+        match $e {
+            Ok(e) => e,
+            Err(errs) => {
+                for e in errs {
+                    $handler.emit_diagnostic(&e);
+                }
+                FatalError.raise()
+            }
+        }
+    }};
+}
+
+pub fn parse_crate_from_file<'a>(input: &Path, sess: &'a ParseSess) -> PResult<'a, ast::Crate> {
+    let mut parser = new_parser_from_file(sess, input, None);
+    parser.parse_crate_mod()
+}
+
+pub fn parse_crate_attrs_from_file<'a>(
+    input: &Path,
+    sess: &'a ParseSess,
+) -> PResult<'a, Vec<ast::Attribute>> {
+    let mut parser = new_parser_from_file(sess, input, None);
+    parser.parse_inner_attributes()
+}
+
+pub fn parse_crate_from_source_str(
+    name: FileName,
+    source: String,
+    sess: &ParseSess,
+) -> PResult<'_, ast::Crate> {
+    new_parser_from_source_str(sess, name, source).parse_crate_mod()
+}
+
+pub fn parse_crate_attrs_from_source_str(
+    name: FileName,
+    source: String,
+    sess: &ParseSess,
+) -> PResult<'_, Vec<ast::Attribute>> {
+    new_parser_from_source_str(sess, name, source).parse_inner_attributes()
+}
+
+pub fn parse_stream_from_source_str(
+    name: FileName,
+    source: String,
+    sess: &ParseSess,
+    override_span: Option<Span>,
+) -> TokenStream {
+    let (stream, mut errors) =
+        source_file_to_stream(sess, sess.source_map().new_source_file(name, source), override_span);
+    emit_unclosed_delims(&mut errors, &sess);
+    stream
+}
+
+/// Creates a new parser from a source string.
+pub fn new_parser_from_source_str(sess: &ParseSess, name: FileName, source: String) -> Parser<'_> {
+    panictry_buffer!(&sess.span_diagnostic, maybe_new_parser_from_source_str(sess, name, source))
+}
+
+/// Creates a new parser from a source string. Returns any buffered errors from lexing the initial
+/// token stream.
+pub fn maybe_new_parser_from_source_str(
+    sess: &ParseSess,
+    name: FileName,
+    source: String,
+) -> Result<Parser<'_>, Vec<Diagnostic>> {
+    maybe_source_file_to_parser(sess, sess.source_map().new_source_file(name, source))
+}
+
+/// Creates a new parser, handling errors as appropriate if the file doesn't exist.
+/// If a span is given, that is used on an error as the as the source of the problem.
+pub fn new_parser_from_file<'a>(sess: &'a ParseSess, path: &Path, sp: Option<Span>) -> Parser<'a> {
+    source_file_to_parser(sess, file_to_source_file(sess, path, sp))
+}
+
+/// Creates a new parser, returning buffered diagnostics if the file doesn't exist,
+/// or from lexing the initial token stream.
+pub fn maybe_new_parser_from_file<'a>(
+    sess: &'a ParseSess,
+    path: &Path,
+) -> Result<Parser<'a>, Vec<Diagnostic>> {
+    let file = try_file_to_source_file(sess, path, None).map_err(|db| vec![db])?;
+    maybe_source_file_to_parser(sess, file)
+}
+
+/// Given a `source_file` and config, returns a parser.
+fn source_file_to_parser(sess: &ParseSess, source_file: Lrc<SourceFile>) -> Parser<'_> {
+    panictry_buffer!(&sess.span_diagnostic, maybe_source_file_to_parser(sess, source_file))
+}
+
+/// Given a `source_file` and config, return a parser. Returns any buffered errors from lexing the
+/// initial token stream.
+fn maybe_source_file_to_parser(
+    sess: &ParseSess,
+    source_file: Lrc<SourceFile>,
+) -> Result<Parser<'_>, Vec<Diagnostic>> {
+    let end_pos = source_file.end_pos;
+    let (stream, unclosed_delims) = maybe_file_to_stream(sess, source_file, None)?;
+    let mut parser = stream_to_parser(sess, stream, None);
+    parser.unclosed_delims = unclosed_delims;
+    if parser.token == token::Eof {
+        parser.token.span = Span::new(end_pos, end_pos, parser.token.span.ctxt());
+    }
+
+    Ok(parser)
+}
+
+// Must preserve old name for now, because `quote!` from the *existing*
+// compiler expands into it.
+pub fn new_parser_from_tts(sess: &ParseSess, tts: Vec<TokenTree>) -> Parser<'_> {
+    stream_to_parser(sess, tts.into_iter().collect(), crate::MACRO_ARGUMENTS)
+}
+
+// Base abstractions
+
+/// Given a session and a path and an optional span (for error reporting),
+/// add the path to the session's source_map and return the new source_file or
+/// error when a file can't be read.
+fn try_file_to_source_file(
+    sess: &ParseSess,
+    path: &Path,
+    spanopt: Option<Span>,
+) -> Result<Lrc<SourceFile>, Diagnostic> {
+    sess.source_map().load_file(path).map_err(|e| {
+        let msg = format!("couldn't read {}: {}", path.display(), e);
+        let mut diag = Diagnostic::new(Level::Fatal, &msg);
+        if let Some(sp) = spanopt {
+            diag.set_span(sp);
+        }
+        diag
+    })
+}
+
+/// Given a session and a path and an optional span (for error reporting),
+/// adds the path to the session's `source_map` and returns the new `source_file`.
+fn file_to_source_file(sess: &ParseSess, path: &Path, spanopt: Option<Span>) -> Lrc<SourceFile> {
+    match try_file_to_source_file(sess, path, spanopt) {
+        Ok(source_file) => source_file,
+        Err(d) => {
+            sess.span_diagnostic.emit_diagnostic(&d);
+            FatalError.raise();
+        }
+    }
+}
+
+/// Given a `source_file`, produces a sequence of token trees.
+pub fn source_file_to_stream(
+    sess: &ParseSess,
+    source_file: Lrc<SourceFile>,
+    override_span: Option<Span>,
+) -> (TokenStream, Vec<lexer::UnmatchedBrace>) {
+    panictry_buffer!(&sess.span_diagnostic, maybe_file_to_stream(sess, source_file, override_span))
+}
+
+/// Given a source file, produces a sequence of token trees. Returns any buffered errors from
+/// parsing the token stream.
+pub fn maybe_file_to_stream(
+    sess: &ParseSess,
+    source_file: Lrc<SourceFile>,
+    override_span: Option<Span>,
+) -> Result<(TokenStream, Vec<lexer::UnmatchedBrace>), Vec<Diagnostic>> {
+    let srdr = lexer::StringReader::new(sess, source_file, override_span);
+    let (token_trees, unmatched_braces) = srdr.into_token_trees();
+
+    match token_trees {
+        Ok(stream) => Ok((stream, unmatched_braces)),
+        Err(err) => {
+            let mut buffer = Vec::with_capacity(1);
+            err.buffer(&mut buffer);
+            // Not using `emit_unclosed_delims` to use `db.buffer`
+            for unmatched in unmatched_braces {
+                if let Some(err) = make_unclosed_delims_error(unmatched, &sess) {
+                    err.buffer(&mut buffer);
+                }
+            }
+            Err(buffer)
+        }
+    }
+}
+
+/// Given a stream and the `ParseSess`, produces a parser.
+pub fn stream_to_parser<'a>(
+    sess: &'a ParseSess,
+    stream: TokenStream,
+    subparser_name: Option<&'static str>,
+) -> Parser<'a> {
+    Parser::new(sess, stream, false, subparser_name)
+}
+
+/// Runs the given subparser `f` on the tokens of the given `attr`'s item.
+pub fn parse_in<'a, T>(
+    sess: &'a ParseSess,
+    tts: TokenStream,
+    name: &'static str,
+    mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+) -> PResult<'a, T> {
+    let mut parser = Parser::new(sess, tts, false, Some(name));
+    let result = f(&mut parser)?;
+    if parser.token != token::Eof {
+        parser.unexpected()?;
+    }
+    Ok(result)
+}
+
+// NOTE(Centril): The following probably shouldn't be here but it acknowledges the
+// fact that architecturally, we are using parsing (read on below to understand why).
+
+pub fn nt_to_tokenstream(nt: &Nonterminal, sess: &ParseSess, span: Span) -> TokenStream {
+    // A `Nonterminal` is often a parsed AST item. At this point we now
+    // need to convert the parsed AST to an actual token stream, e.g.
+    // un-parse it basically.
+    //
+    // Unfortunately there's not really a great way to do that in a
+    // guaranteed lossless fashion right now. The fallback here is to just
+    // stringify the AST node and reparse it, but this loses all span
+    // information.
+    //
+    // As a result, some AST nodes are annotated with the token stream they
+    // came from. Here we attempt to extract these lossless token streams
+    // before we fall back to the stringification.
+    let tokens = match *nt {
+        Nonterminal::NtItem(ref item) => {
+            prepend_attrs(sess, &item.attrs, item.tokens.as_ref(), span)
+        }
+        Nonterminal::NtPat(ref pat) => pat.tokens.clone(),
+        Nonterminal::NtIdent(ident, is_raw) => {
+            Some(tokenstream::TokenTree::token(token::Ident(ident.name, is_raw), ident.span).into())
+        }
+        Nonterminal::NtLifetime(ident) => {
+            Some(tokenstream::TokenTree::token(token::Lifetime(ident.name), ident.span).into())
+        }
+        Nonterminal::NtTT(ref tt) => Some(tt.clone().into()),
+        Nonterminal::NtExpr(ref expr) => {
+            if expr.tokens.is_none() {
+                debug!("missing tokens for expr {:?}", expr);
+            }
+            prepend_attrs(sess, &expr.attrs, expr.tokens.as_ref(), span)
+        }
+        _ => None,
+    };
+
+    // FIXME(#43081): Avoid this pretty-print + reparse hack
+    let source = pprust::nonterminal_to_string(nt);
+    let filename = FileName::macro_expansion_source_code(&source);
+    let tokens_for_real = parse_stream_from_source_str(filename, source, sess, Some(span));
+
+    // During early phases of the compiler the AST could get modified
+    // directly (e.g., attributes added or removed) and the internal cache
+    // of tokens my not be invalidated or updated. Consequently if the
+    // "lossless" token stream disagrees with our actual stringification
+    // (which has historically been much more battle-tested) then we go
+    // with the lossy stream anyway (losing span information).
+    //
+    // Note that the comparison isn't `==` here to avoid comparing spans,
+    // but it *also* is a "probable" equality which is a pretty weird
+    // definition. We mostly want to catch actual changes to the AST
+    // like a `#[cfg]` being processed or some weird `macro_rules!`
+    // expansion.
+    //
+    // What we *don't* want to catch is the fact that a user-defined
+    // literal like `0xf` is stringified as `15`, causing the cached token
+    // stream to not be literal `==` token-wise (ignoring spans) to the
+    // token stream we got from stringification.
+    //
+    // Instead the "probably equal" check here is "does each token
+    // recursively have the same discriminant?" We basically don't look at
+    // the token values here and assume that such fine grained token stream
+    // modifications, including adding/removing typically non-semantic
+    // tokens such as extra braces and commas, don't happen.
+    if let Some(tokens) = tokens {
+        if tokenstream_probably_equal_for_proc_macro(&tokens, &tokens_for_real, sess) {
+            return tokens;
+        }
+        info!(
+            "cached tokens found, but they're not \"probably equal\", \
+                going with stringified version"
+        );
+        info!("cached tokens: {:?}", tokens);
+        info!("reparsed tokens: {:?}", tokens_for_real);
+    }
+    tokens_for_real
+}
+
+// See comments in `Nonterminal::to_tokenstream` for why we care about
+// *probably* equal here rather than actual equality
+//
+// This is otherwise the same as `eq_unspanned`, only recursing with a
+// different method.
+pub fn tokenstream_probably_equal_for_proc_macro(
+    first: &TokenStream,
+    other: &TokenStream,
+    sess: &ParseSess,
+) -> bool {
+    // When checking for `probably_eq`, we ignore certain tokens that aren't
+    // preserved in the AST. Because they are not preserved, the pretty
+    // printer arbitrarily adds or removes them when printing as token
+    // streams, making a comparison between a token stream generated from an
+    // AST and a token stream which was parsed into an AST more reliable.
+    fn semantic_tree(tree: &TokenTree) -> bool {
+        if let TokenTree::Token(token) = tree {
+            if let
+                // The pretty printer tends to add trailing commas to
+                // everything, and in particular, after struct fields.
+                | token::Comma
+                // The pretty printer emits `NoDelim` as whitespace.
+                | token::OpenDelim(DelimToken::NoDelim)
+                | token::CloseDelim(DelimToken::NoDelim)
+                // The pretty printer collapses many semicolons into one.
+                | token::Semi
+                // The pretty printer collapses whitespace arbitrarily and can
+                // introduce whitespace from `NoDelim`.
+                | token::Whitespace
+                // The pretty printer can turn `$crate` into `::crate_name`
+                | token::ModSep = token.kind {
+                return false;
+            }
+        }
+        true
+    }
+
+    // When comparing two `TokenStream`s, we ignore the `IsJoint` information.
+    //
+    // However, `rustc_parse::lexer::tokentrees::TokenStreamBuilder` will
+    // use `Token.glue` on adjacent tokens with the proper `IsJoint`.
+    // Since we are ignoreing `IsJoint`, a 'glued' token (e.g. `BinOp(Shr)`)
+    // and its 'split'/'unglued' compoenents (e.g. `Gt, Gt`) are equivalent
+    // when determining if two `TokenStream`s are 'probably equal'.
+    //
+    // Therefore, we use `break_two_token_op` to convert all tokens
+    // to the 'unglued' form (if it exists). This ensures that two
+    // `TokenStream`s which differ only in how their tokens are glued
+    // will be considered 'probably equal', which allows us to keep spans.
+    //
+    // This is important when the original `TokenStream` contained
+    // extra spaces (e.g. `f :: < Vec < _ > > ( ) ;'). These extra spaces
+    // will be omitted when we pretty-print, which can cause the original
+    // and reparsed `TokenStream`s to differ in the assignment of `IsJoint`,
+    // leading to some tokens being 'glued' together in one stream but not
+    // the other. See #68489 for more details.
+    fn break_tokens(tree: TokenTree) -> impl Iterator<Item = TokenTree> {
+        // In almost all cases, we should have either zero or one levels
+        // of 'unglueing'. However, in some unusual cases, we may need
+        // to iterate breaking tokens mutliple times. For example:
+        // '[BinOpEq(Shr)] => [Gt, Ge] -> [Gt, Gt, Eq]'
+        let mut token_trees: SmallVec<[_; 2]>;
+        if let TokenTree::Token(token) = &tree {
+            let mut out = SmallVec::<[_; 2]>::new();
+            out.push(token.clone());
+            // Iterate to fixpoint:
+            // * We start off with 'out' containing our initial token, and `temp` empty
+            // * If we are able to break any tokens in `out`, then `out` will have
+            //   at least one more element than 'temp', so we will try to break tokens
+            //   again.
+            // * If we cannot break any tokens in 'out', we are done
+            loop {
+                let mut temp = SmallVec::<[_; 2]>::new();
+                let mut changed = false;
+
+                for token in out.into_iter() {
+                    if let Some((first, second)) = token.kind.break_two_token_op() {
+                        temp.push(Token::new(first, DUMMY_SP));
+                        temp.push(Token::new(second, DUMMY_SP));
+                        changed = true;
+                    } else {
+                        temp.push(token);
+                    }
+                }
+                out = temp;
+                if !changed {
+                    break;
+                }
+            }
+            token_trees = out.into_iter().map(TokenTree::Token).collect();
+        } else {
+            token_trees = SmallVec::new();
+            token_trees.push(tree);
+        }
+        token_trees.into_iter()
+    }
+
+    let expand_nt = |tree: TokenTree| {
+        if let TokenTree::Token(Token { kind: TokenKind::Interpolated(nt), span }) = &tree {
+            // When checking tokenstreams for 'probable equality', we are comparing
+            // a captured (from parsing) `TokenStream` to a reparsed tokenstream.
+            // The reparsed Tokenstream will never have `None`-delimited groups,
+            // since they are only ever inserted as a result of macro expansion.
+            // Therefore, inserting a `None`-delimtied group here (when we
+            // convert a nested `Nonterminal` to a tokenstream) would cause
+            // a mismatch with the reparsed tokenstream.
+            //
+            // Note that we currently do not handle the case where the
+            // reparsed stream has a `Parenthesis`-delimited group
+            // inserted. This will cause a spurious mismatch:
+            // issue #75734 tracks resolving this.
+            nt_to_tokenstream(nt, sess, *span).into_trees()
+        } else {
+            TokenStream::new(vec![(tree, IsJoint::NonJoint)]).into_trees()
+        }
+    };
+
+    // Break tokens after we expand any nonterminals, so that we break tokens
+    // that are produced as a result of nonterminal expansion.
+    let mut t1 = first.trees().filter(semantic_tree).flat_map(expand_nt).flat_map(break_tokens);
+    let mut t2 = other.trees().filter(semantic_tree).flat_map(expand_nt).flat_map(break_tokens);
+    for (t1, t2) in t1.by_ref().zip(t2.by_ref()) {
+        if !tokentree_probably_equal_for_proc_macro(&t1, &t2, sess) {
+            return false;
+        }
+    }
+    t1.next().is_none() && t2.next().is_none()
+}
+
+// See comments in `Nonterminal::to_tokenstream` for why we care about
+// *probably* equal here rather than actual equality
+//
+// This is otherwise the same as `eq_unspanned`, only recursing with a
+// different method.
+pub fn tokentree_probably_equal_for_proc_macro(
+    first: &TokenTree,
+    other: &TokenTree,
+    sess: &ParseSess,
+) -> bool {
+    match (first, other) {
+        (TokenTree::Token(token), TokenTree::Token(token2)) => {
+            token_probably_equal_for_proc_macro(token, token2)
+        }
+        (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => {
+            delim == delim2 && tokenstream_probably_equal_for_proc_macro(&tts, &tts2, sess)
+        }
+        _ => false,
+    }
+}
+
+// See comments in `Nonterminal::to_tokenstream` for why we care about
+// *probably* equal here rather than actual equality
+fn token_probably_equal_for_proc_macro(first: &Token, other: &Token) -> bool {
+    if mem::discriminant(&first.kind) != mem::discriminant(&other.kind) {
+        return false;
+    }
+    use rustc_ast::token::TokenKind::*;
+    match (&first.kind, &other.kind) {
+        (&Eq, &Eq)
+        | (&Lt, &Lt)
+        | (&Le, &Le)
+        | (&EqEq, &EqEq)
+        | (&Ne, &Ne)
+        | (&Ge, &Ge)
+        | (&Gt, &Gt)
+        | (&AndAnd, &AndAnd)
+        | (&OrOr, &OrOr)
+        | (&Not, &Not)
+        | (&Tilde, &Tilde)
+        | (&At, &At)
+        | (&Dot, &Dot)
+        | (&DotDot, &DotDot)
+        | (&DotDotDot, &DotDotDot)
+        | (&DotDotEq, &DotDotEq)
+        | (&Comma, &Comma)
+        | (&Semi, &Semi)
+        | (&Colon, &Colon)
+        | (&ModSep, &ModSep)
+        | (&RArrow, &RArrow)
+        | (&LArrow, &LArrow)
+        | (&FatArrow, &FatArrow)
+        | (&Pound, &Pound)
+        | (&Dollar, &Dollar)
+        | (&Question, &Question)
+        | (&Whitespace, &Whitespace)
+        | (&Comment, &Comment)
+        | (&Eof, &Eof) => true,
+
+        (&BinOp(a), &BinOp(b)) | (&BinOpEq(a), &BinOpEq(b)) => a == b,
+
+        (&OpenDelim(a), &OpenDelim(b)) | (&CloseDelim(a), &CloseDelim(b)) => a == b,
+
+        (&DocComment(a1, a2, a3), &DocComment(b1, b2, b3)) => a1 == b1 && a2 == b2 && a3 == b3,
+
+        (&Shebang(a), &Shebang(b)) => a == b,
+
+        (&Literal(a), &Literal(b)) => a == b,
+
+        (&Lifetime(a), &Lifetime(b)) => a == b,
+        (&Ident(a, b), &Ident(c, d)) => {
+            b == d && (a == c || a == kw::DollarCrate || c == kw::DollarCrate)
+        }
+
+        (&Interpolated(..), &Interpolated(..)) => panic!("Unexpanded Interpolated!"),
+
+        _ => panic!("forgot to add a token?"),
+    }
+}
+
+fn prepend_attrs(
+    sess: &ParseSess,
+    attrs: &[ast::Attribute],
+    tokens: Option<&tokenstream::TokenStream>,
+    span: rustc_span::Span,
+) -> Option<tokenstream::TokenStream> {
+    let tokens = tokens?;
+    if attrs.is_empty() {
+        return Some(tokens.clone());
+    }
+    let mut builder = tokenstream::TokenStreamBuilder::new();
+    for attr in attrs {
+        assert_eq!(
+            attr.style,
+            ast::AttrStyle::Outer,
+            "inner attributes should prevent cached tokens from existing"
+        );
+
+        let source = pprust::attribute_to_string(attr);
+        let macro_filename = FileName::macro_expansion_source_code(&source);
+
+        let item = match attr.kind {
+            ast::AttrKind::Normal(ref item) => item,
+            ast::AttrKind::DocComment(..) => {
+                let stream = parse_stream_from_source_str(macro_filename, source, sess, Some(span));
+                builder.push(stream);
+                continue;
+            }
+        };
+
+        // synthesize # [ $path $tokens ] manually here
+        let mut brackets = tokenstream::TokenStreamBuilder::new();
+
+        // For simple paths, push the identifier directly
+        if item.path.segments.len() == 1 && item.path.segments[0].args.is_none() {
+            let ident = item.path.segments[0].ident;
+            let token = token::Ident(ident.name, ident.as_str().starts_with("r#"));
+            brackets.push(tokenstream::TokenTree::token(token, ident.span));
+
+        // ... and for more complicated paths, fall back to a reparse hack that
+        // should eventually be removed.
+        } else {
+            let stream = parse_stream_from_source_str(macro_filename, source, sess, Some(span));
+            brackets.push(stream);
+        }
+
+        brackets.push(item.args.outer_tokens());
+
+        // The span we list here for `#` and for `[ ... ]` are both wrong in
+        // that it encompasses more than each token, but it hopefully is "good
+        // enough" for now at least.
+        builder.push(tokenstream::TokenTree::token(token::Pound, attr.span));
+        let delim_span = tokenstream::DelimSpan::from_single(attr.span);
+        builder.push(tokenstream::TokenTree::Delimited(
+            delim_span,
+            token::DelimToken::Bracket,
+            brackets.build(),
+        ));
+    }
+    builder.push(tokens.clone());
+    Some(builder.build())
+}