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Rollup merge of #139858 - oli-obk:new-const-traits-syntax, r=fee1-dead

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New const traits syntax

This PR only affects the AST and doesn't actually change anything semantically.

All occurrences of `~const` outside of libcore have been replaced by `[const]`. Within libcore we have to wait for rustfmt to be bumped in the bootstrap compiler. This will happen "automatically" (when rustfmt is run) during the bootstrap bump, as rustfmt converts `~const` into `[const]`. After this we can remove the `~const` support from the parser

Caveat discovered during impl: there is no legacy bare trait object recovery for `[const] Trait` as that snippet in type position goes down the slice /array parsing code and will error

r? ``@fee1-dead``

cc ``@nikomatsakis`` ``@traviscross`` ``@compiler-errors``
This commit is contained in:
Matthias Krüger
2025-06-27 22:13:00 +02:00
committed by GitHub
parent fe5f3dedf7 512ff95206
commit 36c2b011cb
243 changed files with 1641 additions and 1571 deletions
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50
compiler/rustc_parse/src/parser/ty.rs
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@@ -885,6 +885,7 @@ impl<'a> Parser<'a> {
|| self.check(exp!(Tilde))
|| self.check_keyword(exp!(For))
|| self.check(exp!(OpenParen))
|| self.check(exp!(OpenBracket))
|| self.check_keyword(exp!(Const))
|| self.check_keyword(exp!(Async))
|| self.check_keyword(exp!(Use))
@@ -982,12 +983,12 @@ impl<'a> Parser<'a> {
Ok(())
}
/// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
/// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `[const] Trait`.
///
/// If no modifiers are present, this does not consume any tokens.
///
/// ```ebnf
/// CONSTNESS = [["~"] "const"]
/// CONSTNESS = [["["] "const" ["]"]]
/// ASYNCNESS = ["async"]
/// POLARITY = ["?" | "!"]
/// ```
@@ -995,18 +996,7 @@ impl<'a> Parser<'a> {
/// See `parse_generic_ty_bound` for the complete grammar of trait bound modifiers.
fn parse_trait_bound_modifiers(&mut self) -> PResult<'a, TraitBoundModifiers> {
let modifier_lo = self.token.span;
let constness = if self.eat(exp!(Tilde)) {
let tilde = self.prev_token.span;
self.expect_keyword(exp!(Const))?;
let span = tilde.to(self.prev_token.span);
self.psess.gated_spans.gate(sym::const_trait_impl, span);
BoundConstness::Maybe(span)
} else if self.eat_keyword(exp!(Const)) {
self.psess.gated_spans.gate(sym::const_trait_impl, self.prev_token.span);
BoundConstness::Always(self.prev_token.span)
} else {
BoundConstness::Never
};
let constness = self.parse_bound_constness()?;
let asyncness = if self.token_uninterpolated_span().at_least_rust_2018()
&& self.eat_keyword(exp!(Async))
@@ -1068,13 +1058,41 @@ impl<'a> Parser<'a> {
Ok(TraitBoundModifiers { constness, asyncness, polarity })
}
pub fn parse_bound_constness(&mut self) -> PResult<'a, BoundConstness> {
// FIXME(const_trait_impl): remove `~const` parser support once bootstrap has the new syntax
// in rustfmt
Ok(if self.eat(exp!(Tilde)) {
let tilde = self.prev_token.span;
self.expect_keyword(exp!(Const))?;
let span = tilde.to(self.prev_token.span);
self.psess.gated_spans.gate(sym::const_trait_impl, span);
BoundConstness::Maybe(span)
} else if self.check(exp!(OpenBracket))
&& self.look_ahead(1, |t| t.is_keyword(kw::Const))
&& self.look_ahead(2, |t| *t == token::CloseBracket)
{
let start = self.prev_token.span;
self.bump();
self.expect_keyword(exp!(Const)).unwrap();
self.bump();
let span = start.to(self.prev_token.span);
self.psess.gated_spans.gate(sym::const_trait_impl, span);
BoundConstness::Maybe(span)
} else if self.eat_keyword(exp!(Const)) {
self.psess.gated_spans.gate(sym::const_trait_impl, self.prev_token.span);
BoundConstness::Always(self.prev_token.span)
} else {
BoundConstness::Never
})
}
/// Parses a type bound according to:
/// ```ebnf
/// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
/// TY_BOUND_NOPAREN = [for<GENERIC_PARAMS> CONSTNESS ASYNCNESS | POLARITY] SIMPLE_PATH
/// ```
///
/// For example, this grammar accepts `for<'a: 'b> ~const ?m::Trait<'a>`.
/// For example, this grammar accepts `for<'a: 'b> [const] ?m::Trait<'a>`.
fn parse_generic_ty_bound(
&mut self,
lo: Span,
@@ -1101,7 +1119,7 @@ impl<'a> Parser<'a> {
}
// Recover erroneous lifetime bound with modifiers or binder.
// e.g. `T: for<'a> 'a` or `T: ~const 'a`.
// e.g. `T: for<'a> 'a` or `T: [const] 'a`.
if self.token.is_lifetime() {
let _: ErrorGuaranteed = self.error_lt_bound_with_modifiers(modifiers, binder_span);
return self.parse_generic_lt_bound(lo, has_parens);