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Update mgca to use type const syntax instead of the #[type_const] attribute. #152324

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Merged
rust-bors merged 1 commit into from
Feb 10, 2026
Merged

Update mgca to use type const syntax instead of the #[type_const] attribute. #152324

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37 changes: 27 additions & 10 deletions compiler/rustc_ast/src/ast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3869,27 +3869,44 @@ pub struct ConstItem {
pub ident: Ident,
pub generics: Generics,
pub ty: Box<Ty>,
pub rhs: Option<ConstItemRhs>,
pub rhs_kind: ConstItemRhsKind,
pub define_opaque: Option<ThinVec<(NodeId, Path)>>,
}

#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
pub enum ConstItemRhs {
TypeConst(AnonConst),
Body(Box<Expr>),
pub enum ConstItemRhsKind {
Body { rhs: Option<Box<Expr>> },
TypeConst { rhs: Option<AnonConst> },
}

impl ConstItemRhs {
pub fn span(&self) -> Span {
self.expr().span
impl ConstItemRhsKind {
pub fn new_body(rhs: Box<Expr>) -> Self {
Self::Body { rhs: Some(rhs) }
}

pub fn span(&self) -> Option<Span> {
Some(self.expr()?.span)
}

pub fn expr(&self) -> Option<&Expr> {
match self {
Self::Body { rhs: Some(body) } => Some(&body),
Self::TypeConst { rhs: Some(anon) } => Some(&anon.value),
_ => None,
}
}

pub fn expr(&self) -> &Expr {
pub fn has_expr(&self) -> bool {
match self {
ConstItemRhs::TypeConst(anon_const) => &anon_const.value,
ConstItemRhs::Body(expr) => expr,
Self::Body { rhs: Some(_) } => true,
Self::TypeConst { rhs: Some(_) } => true,
_ => false,
}
}

pub fn is_type_const(&self) -> bool {
matches!(self, &Self::TypeConst { .. })
}
}

#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_ast/src/visit.rs
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Expand Up @@ -427,7 +427,7 @@ macro_rules! common_visitor_and_walkers {
Const,
ConstBlockItem,
ConstItem,
ConstItemRhs,
ConstItemRhsKind,
Defaultness,
Delegation,
DelegationMac,
Expand Down
35 changes: 24 additions & 11 deletions compiler/rustc_ast_lowering/src/item.rs
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Expand Up @@ -288,7 +288,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
ident,
generics,
ty,
rhs,
rhs_kind,
define_opaque,
}) => {
let ident = self.lower_ident(*ident);
Expand All @@ -301,7 +301,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
ty,
ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy),
);
let rhs = this.lower_const_item_rhs(attrs, rhs.as_ref(), span);
let rhs = this.lower_const_item_rhs(rhs_kind, span);
(ty, rhs)
},
);
Expand Down Expand Up @@ -941,7 +941,12 @@ impl<'hir> LoweringContext<'_, 'hir> {

let (ident, generics, kind, has_default) = match &i.kind {
AssocItemKind::Const(box ConstItem {
ident, generics, ty, rhs, define_opaque, ..
ident,
generics,
ty,
rhs_kind,
define_opaque,
..
}) => {
let (generics, kind) = self.lower_generics(
generics,
Expand All @@ -952,15 +957,18 @@ impl<'hir> LoweringContext<'_, 'hir> {
ty,
ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy),
);
let rhs = rhs
.as_ref()
.map(|rhs| this.lower_const_item_rhs(attrs, Some(rhs), i.span));
hir::TraitItemKind::Const(ty, rhs)
// Trait associated consts don't need an expression/body.
let rhs = if rhs_kind.has_expr() {
Some(this.lower_const_item_rhs(rhs_kind, i.span))
} else {
None
};
hir::TraitItemKind::Const(ty, rhs, rhs_kind.is_type_const().into())
},
);

if define_opaque.is_some() {
if rhs.is_some() {
if rhs_kind.has_expr() {
self.lower_define_opaque(hir_id, &define_opaque);
} else {
self.dcx().span_err(
Expand All @@ -970,7 +978,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
}
}

(*ident, generics, kind, rhs.is_some())
(*ident, generics, kind, rhs_kind.has_expr())
}
AssocItemKind::Fn(box Fn {
sig, ident, generics, body: None, define_opaque, ..
Expand Down Expand Up @@ -1154,7 +1162,12 @@ impl<'hir> LoweringContext<'_, 'hir> {

let (ident, (generics, kind)) = match &i.kind {
AssocItemKind::Const(box ConstItem {
ident, generics, ty, rhs, define_opaque, ..
ident,
generics,
ty,
rhs_kind,
define_opaque,
..
}) => (
*ident,
self.lower_generics(
Expand All @@ -1167,7 +1180,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy),
);
this.lower_define_opaque(hir_id, &define_opaque);
let rhs = this.lower_const_item_rhs(attrs, rhs.as_ref(), i.span);
let rhs = this.lower_const_item_rhs(rhs_kind, i.span);
hir::ImplItemKind::Const(ty, rhs)
},
),
Expand Down
19 changes: 10 additions & 9 deletions compiler/rustc_ast_lowering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2374,15 +2374,20 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {

fn lower_const_item_rhs(
&mut self,
attrs: &[hir::Attribute],
rhs: Option<&ConstItemRhs>,
rhs_kind: &ConstItemRhsKind,
span: Span,
) -> hir::ConstItemRhs<'hir> {
match rhs {
Some(ConstItemRhs::TypeConst(anon)) => {
match rhs_kind {
ConstItemRhsKind::Body { rhs: Some(body) } => {
hir::ConstItemRhs::Body(self.lower_const_body(span, Some(body)))
}
ConstItemRhsKind::Body { rhs: None } => {
hir::ConstItemRhs::Body(self.lower_const_body(span, None))
}
ConstItemRhsKind::TypeConst { rhs: Some(anon) } => {
hir::ConstItemRhs::TypeConst(self.lower_anon_const_to_const_arg_and_alloc(anon))
}
None if find_attr!(attrs, AttributeKind::TypeConst(_)) => {
ConstItemRhsKind::TypeConst { rhs: None } => {
let const_arg = ConstArg {
hir_id: self.next_id(),
kind: hir::ConstArgKind::Error(
Expand All @@ -2392,10 +2397,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
};
hir::ConstItemRhs::TypeConst(self.arena.alloc(const_arg))
}
Some(ConstItemRhs::Body(body)) => {
hir::ConstItemRhs::Body(self.lower_const_body(span, Some(body)))
}
None => hir::ConstItemRhs::Body(self.lower_const_body(span, None)),
}
}

Expand Down
16 changes: 9 additions & 7 deletions compiler/rustc_ast_passes/src/ast_validation.rs
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Expand Up @@ -1361,9 +1361,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
}
});
}
ItemKind::Const(box ConstItem { defaultness, ident, rhs, .. }) => {
ItemKind::Const(box ConstItem { defaultness, ident, rhs_kind, .. }) => {
self.check_defaultness(item.span, *defaultness);
if rhs.is_none() {
if !rhs_kind.has_expr() {
self.dcx().emit_err(errors::ConstWithoutBody {
span: item.span,
replace_span: self.ending_semi_or_hi(item.span),
Expand Down Expand Up @@ -1715,11 +1715,13 @@ impl<'a> Visitor<'a> for AstValidator<'a> {

if let AssocCtxt::Impl { .. } = ctxt {
match &item.kind {
AssocItemKind::Const(box ConstItem { rhs: None, .. }) => {
self.dcx().emit_err(errors::AssocConstWithoutBody {
span: item.span,
replace_span: self.ending_semi_or_hi(item.span),
});
AssocItemKind::Const(box ConstItem { rhs_kind, .. }) => {
if !rhs_kind.has_expr() {
self.dcx().emit_err(errors::AssocConstWithoutBody {
span: item.span,
replace_span: self.ending_semi_or_hi(item.span),
});
}
}
AssocItemKind::Fn(box Fn { body, .. }) => {
if body.is_none() && !self.is_sdylib_interface {
Expand Down
43 changes: 43 additions & 0 deletions compiler/rustc_ast_passes/src/feature_gate.rs
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Expand Up @@ -249,6 +249,14 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ty), .. }) => {
self.check_impl_trait(ty, false)
}
ast::ItemKind::Const(box ast::ConstItem {
rhs_kind: ast::ConstItemRhsKind::TypeConst { .. },
..
}) => {
// Make sure this is only allowed if the feature gate is enabled.
// #![feature(min_generic_const_args)]
gate!(&self, min_generic_const_args, i.span, "top-level `type const` are unstable");
}

_ => {}
}
Expand Down Expand Up @@ -422,6 +430,20 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
}
false
}
ast::AssocItemKind::Const(box ast::ConstItem {
rhs_kind: ast::ConstItemRhsKind::TypeConst { .. },
..
}) => {
// Make sure this is only allowed if the feature gate is enabled.
// #![feature(min_generic_const_args)]
gate!(
&self,
min_generic_const_args,
i.span,
"associated `type const` are unstable"
);
false
}
_ => false,
};
if let ast::Defaultness::Default(_) = i.kind.defaultness() {
Expand Down Expand Up @@ -528,6 +550,27 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
}
}
}
// `mgca_type_const_syntax` is part of `min_generic_const_args` so either
// or both are enabled we don't need to emit a feature error.
if let Some(spans) = spans.get(&sym::mgca_type_const_syntax) {
for span in spans {
if visitor.features.min_generic_const_args()
|| visitor.features.mgca_type_const_syntax()
|| span.allows_unstable(sym::min_generic_const_args)
|| span.allows_unstable(sym::mgca_type_const_syntax)
{
continue;
}
feature_err(
&visitor.sess,
sym::min_generic_const_args,
*span,
"`type const` syntax is experimental",
)
.emit();
}
}

gate_all!(global_registration, "global registration is experimental");
gate_all!(return_type_notation, "return type notation is experimental");
gate_all!(pin_ergonomics, "pinned reference syntax is experimental");
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_ast_pretty/src/pprust/state/item.rs
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Expand Up @@ -221,15 +221,15 @@ impl<'a> State<'a> {
ident,
generics,
ty,
rhs,
rhs_kind,
define_opaque,
}) => {
self.print_item_const(
*ident,
None,
generics,
ty,
rhs.as_ref().map(|ct| ct.expr()),
rhs_kind.expr(),
&item.vis,
ast::Safety::Default,
*defaultness,
Expand Down Expand Up @@ -573,15 +573,15 @@ impl<'a> State<'a> {
ident,
generics,
ty,
rhs,
rhs_kind,
define_opaque,
}) => {
self.print_item_const(
*ident,
None,
generics,
ty,
rhs.as_ref().map(|ct| ct.expr()),
rhs_kind.expr(),
vis,
ast::Safety::Default,
*defaultness,
Expand Down
9 changes: 0 additions & 9 deletions compiler/rustc_attr_parsing/src/attributes/traits.rs
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Expand Up @@ -66,15 +66,6 @@ impl<S: Stage> NoArgsAttributeParser<S> for ParenSugarParser {
const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcParenSugar;
}

pub(crate) struct TypeConstParser;
impl<S: Stage> NoArgsAttributeParser<S> for TypeConstParser {
const PATH: &[Symbol] = &[sym::type_const];
const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
const ALLOWED_TARGETS: AllowedTargets =
AllowedTargets::AllowList(&[Allow(Target::Const), Allow(Target::AssocConst)]);
const CREATE: fn(Span) -> AttributeKind = AttributeKind::TypeConst;
}

// Markers

pub(crate) struct MarkerParser;
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_attr_parsing/src/context.rs
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Expand Up @@ -297,7 +297,6 @@ attribute_parsers!(
Single<WithoutArgs<StdInternalSymbolParser>>,
Single<WithoutArgs<ThreadLocalParser>>,
Single<WithoutArgs<TrackCallerParser>>,
Single<WithoutArgs<TypeConstParser>>,
Single<WithoutArgs<UnsafeSpecializationMarkerParser>>,
// tidy-alphabetical-end
];
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/alloc_error_handler.rs
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Expand Up @@ -43,7 +43,7 @@ pub(crate) fn expand(

// Generate anonymous constant serving as container for the allocator methods.
let const_ty = ecx.ty(sig_span, TyKind::Tup(ThinVec::new()));
let const_body = ast::ConstItemRhs::Body(ecx.expr_block(ecx.block(span, stmts)));
let const_body = ast::ConstItemRhsKind::new_body(ecx.expr_block(ecx.block(span, stmts)));
let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
let const_item = if is_stmt {
Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/eii.rs
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Expand Up @@ -232,7 +232,7 @@ fn generate_default_impl(
span,
underscore,
unit,
ast::ConstItemRhs::Body(ecx.expr_block(ecx.block(span, stmts))),
ast::ConstItemRhsKind::new_body(ecx.expr_block(ecx.block(span, stmts))),
)
};

Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/global_allocator.rs
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Expand Up @@ -47,7 +47,7 @@ pub(crate) fn expand(

// Generate anonymous constant serving as container for the allocator methods.
let const_ty = ecx.ty(ty_span, TyKind::Tup(ThinVec::new()));
let const_body = ast::ConstItemRhs::Body(ecx.expr_block(ecx.block(span, stmts)));
let const_body = ast::ConstItemRhsKind::new_body(ecx.expr_block(ecx.block(span, stmts)));
let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
let const_item = if is_stmt {
Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/proc_macro_harness.rs
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Expand Up @@ -385,7 +385,7 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> Box<ast::Item> {
cx.attr_nested_word(sym::allow, sym::deprecated, span),
]);

let block = ast::ConstItemRhs::Body(cx.expr_block(
let block = ast::ConstItemRhsKind::new_body(cx.expr_block(
cx.block(span, thin_vec![cx.stmt_item(span, krate), cx.stmt_item(span, decls_static)]),
));

Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_builtin_macros/src/test.rs
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Expand Up @@ -289,7 +289,7 @@ pub(crate) fn expand_test_or_bench(
ty: cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
define_opaque: None,
// test::TestDescAndFn {
rhs: Some(ast::ConstItemRhs::Body(
rhs_kind: ast::ConstItemRhsKind::new_body(
cx.expr_struct(
sp,
test_path("TestDescAndFn"),
Expand Down Expand Up @@ -371,7 +371,7 @@ pub(crate) fn expand_test_or_bench(
field("testfn", test_fn), // }
],
), // }
)),
),
}
.into(),
),
Expand Down
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