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Auto merge of #152324 - Keith-Cancel:mgca4, r=BoxyUwU

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Update mgca to use `type const` syntax instead of the `#[type_const]` attribute. 

This PR changes the `#[type_const]` attribute to the `type const` syntax for  https://github.com/rust-lang/rust/issues/132980.

This will fixes https://github.com/rust-lang/rust/issues/151273 and similar issues, since we need to check `type const` of items before expansion. The move to add a syntax was mentioned here: https://github.com/rust-lang/rust/pull/151289#issuecomment-3765241397

The first part of this PR adds support by allowing `type const <IDENT>: <TYPE> { = <EXPR> };` syntax in `rustc_parse/src/parser/item.rs`.

The next part since the AST item does not contain enough information to determine if we have a `type const` was rework `ConstItemRhs` into `ConstItemRhsKind` to store the information since we no longer have the attribute acting as a source of extra data/metadata. 

The hir node `ConstItemRhsKind` current shape mostly works, except in the case of `TraitItemKind` where it is an option. I initially went about giving `hir::ConstItemRhsKind` a similar form the AST, but it touches a lot more lines of code and files so because of that, the less invasive option was to add a simple boolean flag to `TraitItemKind`. 

The forth part of this PR includes adding a query I called `is_rhs_type_const` so that we can handle both local and foreign def_ids. 

The fifth aspect of the PR is adding a `mgca_type_const_syntax` feature gate that is checked before expansion. The standard mgca feature gate is ran after expansion. This feature gate allows for conditional compilation (e.g #[cfg(..)]) of the `type const` syntax  in nightly without `min_generic_const_args` being enabled. 

The last bit is updating all the the tests that used the `#[type_const]` attribute to use the new syntax that failed because of the changes. This is the bulk of touched/edited files in the PR. 

r? @BoxyUwU 
@rustbot label +F-associated_const_equality +F-min_generic_const_args
This commit is contained in:
bors 2026-02-09 22:37:29 +00:00
commit 381e9ef09e
204 changed files with 1014 additions and 906 deletions
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1
compiler/rustc_passes/src/check_attr.rs
View file

@ -358,7 +358,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
| AttributeKind::RustcVarianceOfOpaques
| AttributeKind::ShouldPanic { .. }
| AttributeKind::ThreadLocal
| AttributeKind::TypeConst{..}
| AttributeKind::TypeLengthLimit { .. }
| AttributeKind::UnstableFeatureBound(..)
| AttributeKind::Used { .. }

8
compiler/rustc_passes/src/reachable.rs
View file

@ -145,7 +145,7 @@ impl<'tcx> ReachableContext<'tcx> {
_ => false,
},
Node::TraitItem(trait_method) => match trait_method.kind {
hir::TraitItemKind::Const(_, ref default) => default.is_some(),
hir::TraitItemKind::Const(_, ref default, _) => default.is_some(),
hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
| hir::TraitItemKind::Type(..) => false,
@ -209,7 +209,7 @@ impl<'tcx> ReachableContext<'tcx> {
self.visit_nested_body(body);
}
}
// For #[type_const] we want to evaluate the RHS.
// For `type const` we want to evaluate the RHS.
hir::ItemKind::Const(_, _, _, init @ hir::ConstItemRhs::TypeConst(_)) => {
self.visit_const_item_rhs(init);
}
@ -258,11 +258,11 @@ impl<'tcx> ReachableContext<'tcx> {
}
Node::TraitItem(trait_method) => {
match trait_method.kind {
hir::TraitItemKind::Const(_, None)
hir::TraitItemKind::Const(_, None, _)
| hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
// Keep going, nothing to get exported
}
hir::TraitItemKind::Const(_, Some(rhs)) => self.visit_const_item_rhs(rhs),
hir::TraitItemKind::Const(_, Some(rhs), _) => self.visit_const_item_rhs(rhs),
hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
self.visit_nested_body(body_id);
}