path: root/src/librustdoc/clean/utils.rs

use crate::clean::auto_trait::AutoTraitFinder;
use crate::clean::blanket_impl::BlanketImplFinder;
use crate::clean::{
    inline, Clean, Crate, ExternalCrate, Generic, GenericArg, GenericArgs, ImportSource, Item,
    ItemKind, Lifetime, Path, PathSegment, Primitive, PrimitiveType, Type, TypeBinding, Visibility,
};
use crate::core::DocContext;
use crate::formats::item_type::ItemType;
use crate::visit_lib::LibEmbargoVisitor;

use rustc_ast as ast;
use rustc_ast::token::{self, BinOpToken, DelimToken};
use rustc_ast::tokenstream::{TokenStream, TokenTree};
use rustc_ast_pretty::pprust::state::State as Printer;
use rustc_ast_pretty::pprust::PrintState;
use rustc_data_structures::thin_vec::ThinVec;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LOCAL_CRATE};
use rustc_middle::mir::interpret::ConstValue;
use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
use rustc_middle::ty::{self, DefIdTree, TyCtxt};
use rustc_session::parse::ParseSess;
use rustc_span::source_map::FilePathMapping;
use rustc_span::symbol::{kw, sym, Symbol};
use std::fmt::Write as _;
use std::mem;

#[cfg(test)]
mod tests;

crate fn krate(cx: &mut DocContext<'_>) -> Crate {
    let module = crate::visit_ast::RustdocVisitor::new(cx).visit();

    for &cnum in cx.tcx.crates(()) {
        // Analyze doc-reachability for extern items
        LibEmbargoVisitor::new(cx).visit_lib(cnum);
    }

    // Clean the crate, translating the entire librustc_ast AST to one that is
    // understood by rustdoc.
    let mut module = module.clean(cx);

    match *module.kind {
        ItemKind::ModuleItem(ref module) => {
            for it in &module.items {
                // `compiler_builtins` should be masked too, but we can't apply
                // `#[doc(masked)]` to the injected `extern crate` because it's unstable.
                if it.is_extern_crate()
                    && (it.attrs.has_doc_flag(sym::masked)
                        || cx.tcx.is_compiler_builtins(it.def_id.krate()))
                {
                    cx.cache.masked_crates.insert(it.def_id.krate());
                }
            }
        }
        _ => unreachable!(),
    }

    let local_crate = ExternalCrate { crate_num: LOCAL_CRATE };
    let primitives = local_crate.primitives(cx.tcx);
    let keywords = local_crate.keywords(cx.tcx);
    {
        let m = match *module.kind {
            ItemKind::ModuleItem(ref mut m) => m,
            _ => unreachable!(),
        };
        m.items.extend(primitives.iter().map(|&(def_id, prim)| {
            Item::from_def_id_and_parts(
                def_id,
                Some(prim.as_sym()),
                ItemKind::PrimitiveItem(prim),
                cx,
            )
        }));
        m.items.extend(keywords.into_iter().map(|(def_id, kw)| {
            Item::from_def_id_and_parts(def_id, Some(kw), ItemKind::KeywordItem(kw), cx)
        }));
    }

    Crate { module, primitives, external_traits: cx.external_traits.clone() }
}

fn external_generic_args(
    cx: &mut DocContext<'_>,
    did: DefId,
    has_self: bool,
    bindings: Vec<TypeBinding>,
    substs: SubstsRef<'_>,
) -> GenericArgs {
    let mut skip_self = has_self;
    let mut ty_kind = None;
    let args: Vec<_> = substs
        .iter()
        .filter_map(|kind| match kind.unpack() {
            GenericArgKind::Lifetime(lt) => match lt {
                ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrAnon(_), .. }) => {
                    Some(GenericArg::Lifetime(Lifetime::elided()))
                }
                _ => lt.clean(cx).map(GenericArg::Lifetime),
            },
            GenericArgKind::Type(_) if skip_self => {
                skip_self = false;
                None
            }
            GenericArgKind::Type(ty) => {
                ty_kind = Some(ty.kind());
                Some(GenericArg::Type(ty.clean(cx)))
            }
            GenericArgKind::Const(ct) => Some(GenericArg::Const(Box::new(ct.clean(cx)))),
        })
        .collect();

    if cx.tcx.fn_trait_kind_from_lang_item(did).is_some() {
        let inputs = match ty_kind.unwrap() {
            ty::Tuple(tys) => tys.iter().map(|t| t.expect_ty().clean(cx)).collect(),
            _ => return GenericArgs::AngleBracketed { args, bindings: bindings.into() },
        };
        let output = None;
        // FIXME(#20299) return type comes from a projection now
        // match types[1].kind {
        //     ty::Tuple(ref v) if v.is_empty() => None, // -> ()
        //     _ => Some(types[1].clean(cx))
        // };
        GenericArgs::Parenthesized { inputs, output }
    } else {
        GenericArgs::AngleBracketed { args, bindings: bindings.into() }
    }
}

pub(super) fn external_path(
    cx: &mut DocContext<'_>,
    did: DefId,
    has_self: bool,
    bindings: Vec<TypeBinding>,
    substs: SubstsRef<'_>,
) -> Path {
    let def_kind = cx.tcx.def_kind(did);
    let name = cx.tcx.item_name(did);
    Path {
        res: Res::Def(def_kind, did),
        segments: vec![PathSegment {
            name,
            args: external_generic_args(cx, did, has_self, bindings, substs),
        }],
    }
}

/// Remove the generic arguments from a path.
crate fn strip_path_generics(mut path: Path) -> Path {
    for ps in path.segments.iter_mut() {
        ps.args = GenericArgs::AngleBracketed { args: vec![], bindings: ThinVec::new() }
    }

    path
}

crate fn qpath_to_string(p: &hir::QPath<'_>) -> String {
    let segments = match *p {
        hir::QPath::Resolved(_, path) => &path.segments,
        hir::QPath::TypeRelative(_, segment) => return segment.ident.to_string(),
        hir::QPath::LangItem(lang_item, ..) => return lang_item.name().to_string(),
    };

    let mut s = String::new();
    for (i, seg) in segments.iter().enumerate() {
        if i > 0 {
            s.push_str("::");
        }
        if seg.ident.name != kw::PathRoot {
            s.push_str(seg.ident.as_str());
        }
    }
    s
}

crate fn build_deref_target_impls(cx: &mut DocContext<'_>, items: &[Item], ret: &mut Vec<Item>) {
    let tcx = cx.tcx;

    for item in items {
        let target = match *item.kind {
            ItemKind::TypedefItem(ref t, true) => &t.type_,
            _ => continue,
        };

        if let Some(prim) = target.primitive_type() {
            let _prof_timer = cx.tcx.sess.prof.generic_activity("build_primitive_inherent_impls");
            for &did in prim.impls(tcx).iter().filter(|did| !did.is_local()) {
                inline::build_impl(cx, None, did, None, ret);
            }
        } else if let Type::Path { path } = target {
            let did = path.def_id();
            if !did.is_local() {
                inline::build_impls(cx, None, did, None, ret);
            }
        }
    }
}

crate fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
    use rustc_hir::*;
    debug!("trying to get a name from pattern: {:?}", p);

    Symbol::intern(&match p.kind {
        PatKind::Wild | PatKind::Struct(..) => return kw::Underscore,
        PatKind::Binding(_, _, ident, _) => return ident.name,
        PatKind::TupleStruct(ref p, ..) | PatKind::Path(ref p) => qpath_to_string(p),
        PatKind::Or(pats) => {
            pats.iter().map(|p| name_from_pat(p).to_string()).collect::<Vec<String>>().join(" | ")
        }
        PatKind::Tuple(elts, _) => format!(
            "({})",
            elts.iter().map(|p| name_from_pat(p).to_string()).collect::<Vec<String>>().join(", ")
        ),
        PatKind::Box(p) => return name_from_pat(&*p),
        PatKind::Ref(p, _) => return name_from_pat(&*p),
        PatKind::Lit(..) => {
            warn!(
                "tried to get argument name from PatKind::Lit, which is silly in function arguments"
            );
            return Symbol::intern("()");
        }
        PatKind::Range(..) => return kw::Underscore,
        PatKind::Slice(begin, ref mid, end) => {
            let begin = begin.iter().map(|p| name_from_pat(p).to_string());
            let mid = mid.as_ref().map(|p| format!("..{}", name_from_pat(&**p))).into_iter();
            let end = end.iter().map(|p| name_from_pat(p).to_string());
            format!("[{}]", begin.chain(mid).chain(end).collect::<Vec<_>>().join(", "))
        }
    })
}

crate fn print_const(cx: &DocContext<'_>, n: &ty::Const<'_>) -> String {
    match n.val {
        ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs: _, promoted }) => {
            let mut s = if let Some(def) = def.as_local() {
                let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def.did);
                print_const_expr(cx.tcx, cx.tcx.hir().body_owned_by(hir_id))
            } else {
                inline::print_inlined_const(cx.tcx, def.did)
            };
            if let Some(promoted) = promoted {
                s.push_str(&format!("::{:?}", promoted))
            }
            s
        }
        _ => {
            let mut s = n.to_string();
            // array lengths are obviously usize
            if s.ends_with("_usize") {
                let n = s.len() - "_usize".len();
                s.truncate(n);
                if s.ends_with(": ") {
                    let n = s.len() - ": ".len();
                    s.truncate(n);
                }
            }
            s
        }
    }
}

crate fn print_evaluated_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<String> {
    tcx.const_eval_poly(def_id).ok().and_then(|val| {
        let ty = tcx.type_of(def_id);
        match (val, ty.kind()) {
            (_, &ty::Ref(..)) => None,
            (ConstValue::Scalar(_), &ty::Adt(_, _)) => None,
            (ConstValue::Scalar(_), _) => {
                let const_ = ty::Const::from_value(tcx, val, ty);
                Some(print_const_with_custom_print_scalar(tcx, const_))
            }
            _ => None,
        }
    })
}

fn format_integer_with_underscore_sep(num: &str) -> String {
    let num_chars: Vec<_> = num.chars().collect();
    let mut num_start_index = if num_chars.get(0) == Some(&'-') { 1 } else { 0 };
    let chunk_size = match num[num_start_index..].as_bytes() {
        [b'0', b'b' | b'x', ..] => {
            num_start_index += 2;
            4
        }
        [b'0', b'o', ..] => {
            num_start_index += 2;
            let remaining_chars = num_chars.len() - num_start_index;
            if remaining_chars <= 6 {
                // don't add underscores to Unix permissions like 0755 or 100755
                return num.to_string();
            }
            3
        }
        _ => 3,
    };

    num_chars[..num_start_index]
        .iter()
        .chain(num_chars[num_start_index..].rchunks(chunk_size).rev().intersperse(&['_']).flatten())
        .collect()
}

fn print_const_with_custom_print_scalar(tcx: TyCtxt<'_>, ct: &ty::Const<'_>) -> String {
    // Use a slightly different format for integer types which always shows the actual value.
    // For all other types, fallback to the original `pretty_print_const`.
    match (ct.val, ct.ty.kind()) {
        (ty::ConstKind::Value(ConstValue::Scalar(int)), ty::Uint(ui)) => {
            format!("{}{}", format_integer_with_underscore_sep(&int.to_string()), ui.name_str())
        }
        (ty::ConstKind::Value(ConstValue::Scalar(int)), ty::Int(i)) => {
            let ty = tcx.lift(ct.ty).unwrap();
            let size = tcx.layout_of(ty::ParamEnv::empty().and(ty)).unwrap().size;
            let data = int.assert_bits(size);
            let sign_extended_data = size.sign_extend(data) as i128;

            format!(
                "{}{}",
                format_integer_with_underscore_sep(&sign_extended_data.to_string()),
                i.name_str()
            )
        }
        _ => ct.to_string(),
    }
}

crate fn is_literal_expr(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
    if let hir::Node::Expr(expr) = tcx.hir().get(hir_id) {
        if let hir::ExprKind::Lit(_) = &expr.kind {
            return true;
        }

        if let hir::ExprKind::Unary(hir::UnOp::Neg, expr) = &expr.kind {
            if let hir::ExprKind::Lit(_) = &expr.kind {
                return true;
            }
        }
    }

    false
}

crate fn print_const_expr(tcx: TyCtxt<'_>, body: hir::BodyId) -> String {
    let hir = tcx.hir();
    let value = &hir.body(body).value;

    let snippet = if !value.span.from_expansion() {
        tcx.sess.source_map().span_to_snippet(value.span).ok()
    } else {
        None
    };

    snippet.unwrap_or_else(|| rustc_hir_pretty::id_to_string(&hir, body.hir_id))
}

/// Given a type Path, resolve it to a Type using the TyCtxt
crate fn resolve_type(cx: &mut DocContext<'_>, path: Path) -> Type {
    debug!("resolve_type({:?})", path);

    match path.res {
        Res::PrimTy(p) => Primitive(PrimitiveType::from(p)),
        Res::SelfTy(..) if path.segments.len() == 1 => Generic(kw::SelfUpper),
        Res::Def(DefKind::TyParam, _) if path.segments.len() == 1 => Generic(path.segments[0].name),
        _ => {
            let _ = register_res(cx, path.res);
            Type::Path { path }
        }
    }
}

crate fn get_auto_trait_and_blanket_impls(
    cx: &mut DocContext<'_>,
    item_def_id: DefId,
) -> impl Iterator<Item = Item> {
    let auto_impls = cx
        .sess()
        .prof
        .generic_activity("get_auto_trait_impls")
        .run(|| AutoTraitFinder::new(cx).get_auto_trait_impls(item_def_id));
    let blanket_impls = cx
        .sess()
        .prof
        .generic_activity("get_blanket_impls")
        .run(|| BlanketImplFinder { cx }.get_blanket_impls(item_def_id));
    auto_impls.into_iter().chain(blanket_impls)
}

/// If `res` has a documentation page associated, store it in the cache.
///
/// This is later used by [`href()`] to determine the HTML link for the item.
///
/// [`href()`]: crate::html::format::href
crate fn register_res(cx: &mut DocContext<'_>, res: Res) -> DefId {
    use DefKind::*;
    debug!("register_res({:?})", res);

    let (did, kind) = match res {
        // These should be added to the cache using `record_extern_fqn`.
        Res::Def(
            kind @ (AssocTy | AssocFn | AssocConst | Variant | Fn | TyAlias | Enum | Trait | Struct
            | Union | Mod | ForeignTy | Const | Static | Macro(..) | TraitAlias),
            i,
        ) => (i, kind.into()),
        // This is part of a trait definition; document the trait.
        Res::SelfTy(Some(trait_def_id), _) => (trait_def_id, ItemType::Trait),
        // This is an inherent impl; it doesn't have its own page.
        Res::SelfTy(None, Some((impl_def_id, _))) => return impl_def_id,
        Res::SelfTy(None, None)
        | Res::PrimTy(_)
        | Res::ToolMod
        | Res::SelfCtor(_)
        | Res::Local(_)
        | Res::NonMacroAttr(_)
        | Res::Err => return res.def_id(),
        Res::Def(
            TyParam | ConstParam | Ctor(..) | ExternCrate | Use | ForeignMod | AnonConst
            | InlineConst | OpaqueTy | Field | LifetimeParam | GlobalAsm | Impl | Closure
            | Generator,
            id,
        ) => return id,
    };
    if did.is_local() {
        return did;
    }
    inline::record_extern_fqn(cx, did, kind);
    if let ItemType::Trait = kind {
        inline::record_extern_trait(cx, did);
    }
    did
}

crate fn resolve_use_source(cx: &mut DocContext<'_>, path: Path) -> ImportSource {
    ImportSource {
        did: if path.res.opt_def_id().is_none() { None } else { Some(register_res(cx, path.res)) },
        path,
    }
}

crate fn enter_impl_trait<F, R>(cx: &mut DocContext<'_>, f: F) -> R
where
    F: FnOnce(&mut DocContext<'_>) -> R,
{
    let old_bounds = mem::take(&mut cx.impl_trait_bounds);
    let r = f(cx);
    assert!(cx.impl_trait_bounds.is_empty());
    cx.impl_trait_bounds = old_bounds;
    r
}

/// Find the nearest parent module of a [`DefId`].
crate fn find_nearest_parent_module(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
    if def_id.is_top_level_module() {
        // The crate root has no parent. Use it as the root instead.
        Some(def_id)
    } else {
        let mut current = def_id;
        // The immediate parent might not always be a module.
        // Find the first parent which is.
        while let Some(parent) = tcx.parent(current) {
            if tcx.def_kind(parent) == DefKind::Mod {
                return Some(parent);
            }
            current = parent;
        }
        None
    }
}

/// Checks for the existence of `hidden` in the attribute below if `flag` is `sym::hidden`:
///
/// ```
/// #[doc(hidden)]
/// pub fn foo() {}
/// ```
///
/// This function exists because it runs on `hir::Attributes` whereas the other is a
/// `clean::Attributes` method.
crate fn has_doc_flag(attrs: ty::Attributes<'_>, flag: Symbol) -> bool {
    attrs.iter().any(|attr| {
        attr.has_name(sym::doc)
            && attr.meta_item_list().map_or(false, |l| rustc_attr::list_contains_name(&l, flag))
    })
}

/// A link to `doc.rust-lang.org` that includes the channel name. Use this instead of manual links
/// so that the channel is consistent.
///
/// Set by `bootstrap::Builder::doc_rust_lang_org_channel` in order to keep tests passing on beta/stable.
crate const DOC_RUST_LANG_ORG_CHANNEL: &str = env!("DOC_RUST_LANG_ORG_CHANNEL");

/// Render a sequence of macro arms in a format suitable for displaying to the user
/// as part of an item declaration.
pub(super) fn render_macro_arms<'a>(
    tcx: TyCtxt<'_>,
    matchers: impl Iterator<Item = &'a TokenTree>,
    arm_delim: &str,
) -> String {
    let mut out = String::new();
    for matcher in matchers {
        writeln!(out, "    {} => {{ ... }}{}", render_macro_matcher(tcx, matcher), arm_delim)
            .unwrap();
    }
    out
}

/// Render a macro matcher in a format suitable for displaying to the user
/// as part of an item declaration.
pub(super) fn render_macro_matcher(tcx: TyCtxt<'_>, matcher: &TokenTree) -> String {
    if let Some(snippet) = snippet_equal_to_token(tcx, matcher) {
        // If the original source code is known, we display the matcher exactly
        // as present in the source code.
        return snippet;
    }

    // If the matcher is macro-generated or some other reason the source code
    // snippet is not available, we attempt to nicely render the token tree.
    let mut printer = Printer::new();

    // If the inner ibox fits on one line, we get:
    //
    //     macro_rules! macroname {
    //         (the matcher) => {...};
    //     }
    //
    // If the inner ibox gets wrapped, the cbox will break and get indented:
    //
    //     macro_rules! macroname {
    //         (
    //             the matcher ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    //             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~!
    //         ) => {...};
    //     }
    printer.cbox(8);
    printer.word("(");
    printer.zerobreak();
    printer.ibox(0);
    match matcher {
        TokenTree::Delimited(_span, _delim, tts) => print_tts(&mut printer, tts),
        // Matcher which is not a Delimited is unexpected and should've failed
        // to compile, but we render whatever it is wrapped in parens.
        TokenTree::Token(_) => print_tt(&mut printer, matcher),
    }
    printer.end();
    printer.break_offset_if_not_bol(0, -4);
    printer.word(")");
    printer.end();
    printer.s.eof()
}

/// Find the source snippet for this token's Span, reparse it, and return the
/// snippet if the reparsed TokenTree matches the argument TokenTree.
fn snippet_equal_to_token(tcx: TyCtxt<'_>, matcher: &TokenTree) -> Option<String> {
    // Find what rustc thinks is the source snippet.
    // This may not actually be anything meaningful if this matcher was itself
    // generated by a macro.
    let source_map = tcx.sess.source_map();
    let span = matcher.span();
    let snippet = source_map.span_to_snippet(span).ok()?;

    // Create a Parser.
    let sess = ParseSess::new(FilePathMapping::empty());
    let file_name = source_map.span_to_filename(span);
    let mut parser =
        match rustc_parse::maybe_new_parser_from_source_str(&sess, file_name, snippet.clone()) {
            Ok(parser) => parser,
            Err(diagnostics) => {
                for mut diagnostic in diagnostics {
                    diagnostic.cancel();
                }
                return None;
            }
        };

    // Reparse a single token tree.
    let mut reparsed_trees = match parser.parse_all_token_trees() {
        Ok(reparsed_trees) => reparsed_trees,
        Err(mut diagnostic) => {
            diagnostic.cancel();
            return None;
        }
    };
    if reparsed_trees.len() != 1 {
        return None;
    }
    let reparsed_tree = reparsed_trees.pop().unwrap();

    // Compare against the original tree.
    if reparsed_tree.eq_unspanned(matcher) { Some(snippet) } else { None }
}

fn print_tt(printer: &mut Printer<'_>, tt: &TokenTree) {
    match tt {
        TokenTree::Token(token) => {
            let token_str = printer.token_to_string(token);
            printer.word(token_str);
            if let token::DocComment(..) = token.kind {
                printer.hardbreak()
            }
        }
        TokenTree::Delimited(_span, delim, tts) => {
            let open_delim = printer.token_kind_to_string(&token::OpenDelim(*delim));
            printer.word(open_delim);
            if !tts.is_empty() {
                if *delim == DelimToken::Brace {
                    printer.space();
                }
                print_tts(printer, tts);
                if *delim == DelimToken::Brace {
                    printer.space();
                }
            }
            let close_delim = printer.token_kind_to_string(&token::CloseDelim(*delim));
            printer.word(close_delim);
        }
    }
}

fn print_tts(printer: &mut Printer<'_>, tts: &TokenStream) {
    #[derive(Copy, Clone, PartialEq)]
    enum State {
        Start,
        Dollar,
        DollarIdent,
        DollarIdentColon,
        DollarParen,
        DollarParenSep,
        Pound,
        PoundBang,
        Ident,
        Other,
    }

    use State::*;

    let mut state = Start;
    for tt in tts.trees() {
        let (needs_space, next_state) = match &tt {
            TokenTree::Token(tt) => match (state, &tt.kind) {
                (Dollar, token::Ident(..)) => (false, DollarIdent),
                (DollarIdent, token::Colon) => (false, DollarIdentColon),
                (DollarIdentColon, token::Ident(..)) => (false, Other),
                (
                    DollarParen,
                    token::BinOp(BinOpToken::Plus | BinOpToken::Star) | token::Question,
                ) => (false, Other),
                (DollarParen, _) => (false, DollarParenSep),
                (DollarParenSep, token::BinOp(BinOpToken::Plus | BinOpToken::Star)) => {
                    (false, Other)
                }
                (Pound, token::Not) => (false, PoundBang),
                (_, token::Ident(symbol, /* is_raw */ false))
                    if !usually_needs_space_between_keyword_and_open_delim(*symbol) =>
                {
                    (true, Ident)
                }
                (_, token::Comma | token::Semi) => (false, Other),
                (_, token::Dollar) => (true, Dollar),
                (_, token::Pound) => (true, Pound),
                (_, _) => (true, Other),
            },
            TokenTree::Delimited(_, delim, _) => match (state, delim) {
                (Dollar, DelimToken::Paren) => (false, DollarParen),
                (Pound | PoundBang, DelimToken::Bracket) => (false, Other),
                (Ident, DelimToken::Paren | DelimToken::Bracket) => (false, Other),
                (_, _) => (true, Other),
            },
        };
        if state != Start && needs_space {
            printer.space();
        }
        print_tt(printer, &tt);
        state = next_state;
    }
}

// This rough subset of keywords is listed here to distinguish tokens resembling
// `f(0)` (no space between ident and paren) from tokens resembling `if let (0,
// 0) = x` (space between ident and paren).
fn usually_needs_space_between_keyword_and_open_delim(symbol: Symbol) -> bool {
    match symbol.as_str() {
        "as" | "box" | "break" | "const" | "continue" | "crate" | "else" | "enum" | "extern"
        | "for" | "if" | "impl" | "in" | "let" | "loop" | "macro" | "match" | "mod" | "move"
        | "mut" | "ref" | "return" | "static" | "struct" | "trait" | "type" | "unsafe" | "use"
        | "where" | "while" | "yield" => true,
        _ => false,
    }
}

pub(super) fn display_macro_source(
    cx: &mut DocContext<'_>,
    name: Symbol,
    def: &ast::MacroDef,
    def_id: DefId,
    vis: Visibility,
) -> String {
    let tts: Vec<_> = def.body.inner_tokens().into_trees().collect();
    // Extract the spans of all matchers. They represent the "interface" of the macro.
    let matchers = tts.chunks(4).map(|arm| &arm[0]);

    if def.macro_rules {
        format!("macro_rules! {} {{\n{}}}", name, render_macro_arms(cx.tcx, matchers, ";"))
    } else {
        if matchers.len() <= 1 {
            format!(
                "{}macro {}{} {{\n    ...\n}}",
                vis.to_src_with_space(cx.tcx, def_id),
                name,
                matchers.map(|matcher| render_macro_matcher(cx.tcx, matcher)).collect::<String>(),
            )
        } else {
            format!(
                "{}macro {} {{\n{}}}",
                vis.to_src_with_space(cx.tcx, def_id),
                name,
                render_macro_arms(cx.tcx, matchers, ","),
            )
        }
    }
}