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unify the AST repr of type const and const RHS #159596

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unify the AST repr of type const and const RHS #159596

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42 changes: 7 additions & 35 deletions compiler/rustc_ast/src/ast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4010,44 +4010,16 @@ pub struct ConstItem {
pub ident: Ident,
pub generics: Generics,
pub ty: Box<Ty>,
pub rhs_kind: ConstItemRhsKind,
pub body: Option<Box<Expr>>,
#[visitable(ignore)]
pub kind: ConstItemKind,

@khyperia khyperia Jul 20, 2026 •
edited by rustbot
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these names are all bikesheddable, fwiw, just kinda kept the names that were there before.

  • body or expr?
  • ConstItemKind::Body or ConstItemKind::Normal? Or Regular or Standard or Plain or...
  • kind or something specific to, like, is_type_const: TypeConstness::{Yes, No}?
  • or just, is_type_const: bool?

View changes since the review

@BoxyUwU BoxyUwU Jul 22, 2026

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I like enums instead of bools ✨

pub define_opaque: Option<ThinVec<(NodeId, Path)>>,
}

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

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 has_expr(&self) -> bool {
match self {
Self::Body { rhs: Some(_) } => true,
Self::TypeConst { rhs: Some(_) } => true,
_ => false,
}
}

pub fn is_type_const(&self) -> bool {
matches!(self, &Self::TypeConst { .. })
}
#[derive(Clone, Copy, Encodable, Decodable, Debug, PartialEq, Eq)]
pub enum ConstItemKind {
Body,
TypeConst,
}

#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_ast/src/visit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -427,7 +427,6 @@ macro_rules! common_visitor_and_walkers {
Const,
ConstBlockItem,
ConstItem,
ConstItemRhsKind,
Defaultness,
Delegation,
DelegationMac,
Expand Down
21 changes: 12 additions & 9 deletions compiler/rustc_ast_lowering/src/item.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -270,7 +270,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
ident,
generics,
ty,
rhs_kind,
body,
kind,
define_opaque,
}) => {
let ident = self.lower_ident(*ident);
Expand All @@ -282,7 +283,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
ty,
ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy),
);
let rhs = this.lower_const_item_rhs(rhs_kind, span);
let rhs = this.lower_const_item_rhs(body, *kind, span);
(ty, rhs)
},
);
Expand Down Expand Up @@ -918,7 +919,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
ident,
generics,
ty,
rhs_kind,
body,
kind,
define_opaque,
..
}) => {
Expand All @@ -931,8 +933,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy),
);
// 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))
let rhs = if body.is_some() {
Some(this.lower_const_item_rhs(body, *kind, i.span))
} else {
None
};
Expand All @@ -941,7 +943,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
);

if define_opaque.is_some() {
if rhs_kind.has_expr() {
if body.is_some() {
self.lower_define_opaque(hir_id, &define_opaque);
} else {
self.dcx().span_err(
Expand All @@ -951,7 +953,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
}
}

(*ident, generics, kind, rhs_kind.has_expr())
(*ident, generics, kind, body.is_some())
}
AssocItemKind::Fn(Fn { sig, ident, generics, body: None, define_opaque, .. }) => {
// FIXME(contracts): Deny contract here since it won't apply to
Expand Down Expand Up @@ -1180,7 +1182,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
ident,
generics,
ty,
rhs_kind,
body,
kind,
define_opaque,
..
}) => (
Expand All @@ -1194,7 +1197,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy),
);
this.lower_define_opaque(hir_id, &define_opaque);
let rhs = this.lower_const_item_rhs(rhs_kind, i.span);
let rhs = this.lower_const_item_rhs(body, *kind, i.span);
hir::ImplItemKind::Const(ty, rhs)
},
),
Expand Down
20 changes: 9 additions & 11 deletions compiler/rustc_ast_lowering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2671,28 +2671,26 @@ impl<'hir> LoweringContext<'_, 'hir> {

fn lower_const_item_rhs(
&mut self,
rhs_kind: &ConstItemRhsKind,
body: &Option<Box<Expr>>,
kind: ConstItemKind,
span: Span,
) -> hir::ConstItemRhs<'hir> {
match rhs_kind {
ConstItemRhsKind::Body { rhs: Some(body) } => {
hir::ConstItemRhs::Body(self.lower_const_body(span, Some(body)))
match (body, kind) {
(body, ConstItemKind::Body) => {
hir::ConstItemRhs::Body(self.lower_const_body(span, body.as_deref()))
}
ConstItemRhsKind::Body { rhs: None } => {
hir::ConstItemRhs::Body(self.lower_const_body(span, None))
}
ConstItemRhsKind::TypeConst { rhs: Some(anon) } => {
(Some(body), ConstItemKind::TypeConst) => {
hir::ConstItemRhs::TypeConst(self.arena.alloc(
match self.can_lower_expr_to_const_arg_direct(
&anon.value,
&body,
DirectConstArgContext::MacrolessMinGenericConstArgs,
) {
Ok(()) => self.lower_expr_to_const_arg_direct(&anon.value, Some(anon.id)),
Ok(()) => self.lower_expr_to_const_arg_direct(&body, None),
Err(err) => err.emit(self),
},
))
}
ConstItemRhsKind::TypeConst { rhs: None } => {
(None, ConstItemKind::TypeConst) => {
let const_arg = ConstArg {
hir_id: self.next_id(),
kind: hir::ConstArgKind::Error(
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_ast_passes/src/ast_validation.rs
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Expand Up @@ -1544,9 +1544,9 @@ impl Visitor<'_> for AstValidator<'_> {
visit::walk_item(this, item)
});
}
ItemKind::Const(ConstItem { defaultness, ident, rhs_kind, .. }) => {
ItemKind::Const(ConstItem { defaultness, ident, body, .. }) => {
self.check_defaultness(item.span, *defaultness, AllowDefault::No, AllowFinal::No);
if !rhs_kind.has_expr() {
if body.is_none() {
self.dcx().emit_err(diagnostics::ConstWithoutBody {
span: item.span,
replace_span: self.ending_semi_or_hi(item.span),
Expand Down Expand Up @@ -1941,8 +1941,8 @@ impl Visitor<'_> for AstValidator<'_> {

if let AssocCtxt::Impl { .. } = ctxt {
match &item.kind {
AssocItemKind::Const(ConstItem { rhs_kind, .. }) => {
if !rhs_kind.has_expr() {
AssocItemKind::Const(ConstItem { body, .. }) => {
if body.is_none() {
self.dcx().emit_err(diagnostics::AssocConstWithoutBody {
span: item.span,
replace_span: self.ending_semi_or_hi(item.span),
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_ast_passes/src/feature_gate.rs
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Expand Up @@ -220,8 +220,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
self.check_impl_trait(ty, false)
}
ast::ItemKind::Const(ast::ConstItem {
rhs_kind: ast::ConstItemRhsKind::TypeConst { .. },
..
kind: ast::ConstItemKind::TypeConst, ..
}) => {
// Make sure this is only allowed if the feature gate is enabled.
// #![feature(min_generic_const_args)]
Expand Down Expand Up @@ -400,7 +399,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
false
}
ast::AssocItemKind::Const(ast::ConstItem {
rhs_kind: ast::ConstItemRhsKind::TypeConst { rhs },
body,
kind: ast::ConstItemKind::TypeConst,
..
}) => {
// Make sure this is only allowed if the feature gate is enabled.
Expand All @@ -409,7 +409,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
// Make sure associated `type const` defaults in traits are only allowed
// if the feature gate is enabled.
// #![feature(associated_type_defaults)]
if ctxt == AssocCtxt::Trait && rhs.is_some() {
if ctxt == AssocCtxt::Trait && body.is_some() {
gate!(
self,
associated_type_defaults,
Expand Down
10 changes: 6 additions & 4 deletions compiler/rustc_ast_pretty/src/pprust/state/item.rs
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Expand Up @@ -229,15 +229,16 @@ impl<'a> State<'a> {
ident,
generics,
ty,
rhs_kind,
body,
kind: _,
define_opaque,
}) => {
self.print_item_const(
*ident,
None,
generics,
ty,
rhs_kind.expr(),
body.as_deref(),
&item.vis,
ast::Safety::Default,
*defaultness,
Expand Down Expand Up @@ -617,15 +618,16 @@ impl<'a> State<'a> {
ident,
generics,
ty,
rhs_kind,
body,
kind: _,
define_opaque,
}) => {
self.print_item_const(
*ident,
None,
generics,
ty,
rhs_kind.expr(),
body.as_deref(),
vis,
ast::Safety::Default,
*defaultness,
Expand Down
10 changes: 8 additions & 2 deletions compiler/rustc_builtin_macros/src/alloc_error_handler.rs
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Expand Up @@ -43,8 +43,14 @@ 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::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_body = ecx.expr_block(ecx.block(span, stmts));
let const_item = ecx.item_const(
span,
Ident::new(kw::Underscore, span),
const_ty,
Some(const_body),
ast::ConstItemKind::Body,
);
let const_item = if is_stmt {
Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
} else {
Expand Down
3 changes: 2 additions & 1 deletion compiler/rustc_builtin_macros/src/eii.rs
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Expand Up @@ -335,7 +335,8 @@ fn generate_default_impl(
span,
underscore,
unit,
ast::ConstItemRhsKind::new_body(ecx.expr_block(ecx.block(span, stmts))),
Some(ecx.expr_block(ecx.block(span, stmts))),
ast::ConstItemKind::Body,
)
};

Expand Down
10 changes: 8 additions & 2 deletions compiler/rustc_builtin_macros/src/global_allocator.rs
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Expand Up @@ -54,8 +54,14 @@ 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::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_body = ecx.expr_block(ecx.block(span, stmts));
let const_item = ecx.item_const(
span,
Ident::new(kw::Underscore, span),
const_ty,
Some(const_body),
ast::ConstItemKind::Body,
);
let const_item = if is_stmt {
Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
} else {
Expand Down
7 changes: 4 additions & 3 deletions compiler/rustc_builtin_macros/src/proc_macro_harness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -361,15 +361,16 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> Box<ast::Item> {
cx.attr_nested_word(sym::allow, sym::deprecated, span),
]);

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

let anon_constant = cx.item_const(
span,
Ident::new(kw::Underscore, span),
cx.ty(span, ast::TyKind::Tup(ThinVec::new())),
block,
Some(block),
ast::ConstItemKind::Body,
);

// Integrate the new item into existing module structures.
Expand Down
3 changes: 2 additions & 1 deletion compiler/rustc_builtin_macros/src/test.rs
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Expand Up @@ -286,8 +286,9 @@ pub(crate) fn expand_test_or_bench(
generics: ast::Generics::default(),
ty: cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
define_opaque: None,
kind: ast::ConstItemKind::Body,
// test::TestDescAndFn {
rhs_kind: ast::ConstItemRhsKind::new_body(
body: Some(
cx.expr_struct(
sp,
test_path("TestDescAndFn"),
Expand Down
6 changes: 4 additions & 2 deletions compiler/rustc_expand/src/build.rs
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Expand Up @@ -719,7 +719,8 @@ impl<'a> ExtCtxt<'a> {
span: Span,
ident: Ident,
ty: Box<ast::Ty>,
rhs_kind: ast::ConstItemRhsKind,
body: Option<Box<Expr>>,
kind: ast::ConstItemKind,
) -> Box<ast::Item> {
let defaultness = ast::Defaultness::Implicit;
self.item(
Expand All @@ -732,7 +733,8 @@ impl<'a> ExtCtxt<'a> {
// FIXME(generic_const_items): Pass the generics as a parameter.
generics: ast::Generics::default(),
ty,
rhs_kind,
body,
kind,
define_opaque: None,
}
.into(),
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_lint/src/unused.rs
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Expand Up @@ -510,8 +510,8 @@ trait UnusedDelimLint {
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
use ast::ItemKind::*;

let expr = if let Const(ast::ConstItem { rhs_kind, .. }) = &item.kind {
if let Some(e) = rhs_kind.expr() { e } else { return }
let expr = if let Const(ast::ConstItem { body: Some(expr), .. }) = &item.kind {
expr
} else if let Static(ast::StaticItem { expr: Some(expr), .. }) = &item.kind {
expr
} else {
Expand Down
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