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Do not consider _ to be an expression for macro_rules!

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Chayim Refael Friedman 2022-03-02 01:50:54 +00:00 committed by GitHub
parent d9f0731bd2
commit 10d30be331
1 changed files with 11 additions and 1 deletions
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12
crates/mbe/src/expander/matcher.rs
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@ -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 {