diff options
| -rw-r--r-- | crates/mbe/src/expander/matcher.rs | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/crates/mbe/src/expander/matcher.rs b/crates/mbe/src/expander/matcher.rs index 944d3ef87d8..aefb3d059ff 100644 --- a/crates/mbe/src/expander/matcher.rs +++ b/crates/mbe/src/expander/matcher.rs @@ -690,9 +690,19 @@ fn match_meta_var(kind: &str, input: &mut TtIter) -> ExpandResult<Option<Fragmen "item" => parser::PrefixEntryPoint::Item, "vis" => parser::PrefixEntryPoint::Vis, "expr" => { + // `expr` should not match underscores. + // HACK: Macro expansion should not be done using "rollback and try another alternative". + // rustc [explicitly checks the next token][0]. + // [0]: https://github.com/rust-lang/rust/blob/f0c4da499/compiler/rustc_expand/src/mbe/macro_parser.rs#L576 + match input.peek_n(0) { + Some(tt::TokenTree::Leaf(tt::Leaf::Ident(it))) if it.text == "_" => { + return ExpandResult::only_err(ExpandError::NoMatchingRule) + } + _ => {} + }; return input .expect_fragment(parser::PrefixEntryPoint::Expr) - .map(|tt| tt.map(Fragment::Expr)) + .map(|tt| tt.map(Fragment::Expr)); } _ => { let tt_result = match kind { |