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Rollup merge of #126697 - vincenzopalazzo:macros/find_the_expression_tok, r=eholk,compiler-errors

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[RFC] mbe: consider the `_` in 2024 an expression

This commit is adding the possibility to parse the `_` as an expression inside the esition 2024.

Link: https://rust-lang.zulipchat.com/#narrow/stream/404510-wg-macros/topic/supporting.20.60_.60.20expressions

Issue https://github.com/rust-lang/rust/issues/123742

r? `@eholk`
This commit is contained in:
Matthias Krüger 2024-07-31 23:20:09 +02:00 • committed by GitHub
commit 3acd910036
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4 changed files with 83 additions and 1 deletions
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11
compiler/rustc_parse/src/parser/nonterminal.rs
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@ -39,6 +39,7 @@ impl<'a> Parser<'a> {
}
match kind {
// `expr_2021` and earlier
NonterminalKind::Expr(Expr2021 { .. }) => {
token.can_begin_expr()
// This exception is here for backwards compatibility.
@ -46,8 +47,16 @@ impl<'a> Parser<'a> {
// This exception is here for backwards compatibility.
&& !token.is_keyword(kw::Const)
}
// Current edition expressions
NonterminalKind::Expr(Expr) => {
token.can_begin_expr()
// In Edition 2024, `_` is considered an expression, so we
// need to allow it here because `token.can_begin_expr()` does
// not consider `_` to be an expression.
//
// Because `can_begin_expr` is used elsewhere, we need to reduce
// the scope of where the `_` is considered an expression to
// just macro parsing code.
(token.can_begin_expr() || token.is_keyword(kw::Underscore))
// This exception is here for backwards compatibility.
&& !token.is_keyword(kw::Let)
}