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mgca: Lower all const paths as ConstArgKind::Path

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When `#![feature(min_generic_const_args)]` is enabled, we now lower all
const paths in generic arg position to `hir::ConstArgKind::Path`. We
then lower assoc const paths to `ty::ConstKind::Unevaluated` since we
can no longer use the anon const expression lowering machinery. In the
process of implementing this, I factored out `hir_ty_lowering` code that
is now shared between lowering assoc types and assoc consts.

This PR also introduces a `#[type_const]` attribute for trait assoc
consts that are allowed as const args. However, we still need to
implement code to check that assoc const definitions satisfy
`#[type_const]` if present (basically is it a const path or a
monomorphic anon const).
This commit is contained in:
Noah Lev 2025-01-06 21:15:56 -08:00
parent 2010bba886
commit 177e7ff548
35 changed files with 602 additions and 148 deletions
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17
compiler/rustc_ast_lowering/src/lib.rs
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@ -1094,7 +1094,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
.and_then(|partial_res| partial_res.full_res())
{
if !res.matches_ns(Namespace::TypeNS)
&& path.is_potential_trivial_const_arg()
&& path.is_potential_trivial_const_arg(false)
{
debug!(
"lower_generic_arg: Lowering type argument as const argument: {:?}",
@ -2061,8 +2061,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
) -> &'hir hir::ConstArg<'hir> {
let tcx = self.tcx;
// FIXME(min_generic_const_args): we only allow one-segment const paths for now
let ct_kind = if path.is_potential_trivial_const_arg()
let ct_kind = if path
.is_potential_trivial_const_arg(tcx.features().min_generic_const_args())
&& (tcx.features().min_generic_const_args()
|| matches!(res, Res::Def(DefKind::ConstParam, _)))
{
@ -2072,7 +2072,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
path,
ParamMode::Optional,
AllowReturnTypeNotation::No,
// FIXME(min_generic_const_args): update for `fn foo() -> Bar<FOO<impl Trait>>` support
// FIXME(mgca): update for `fn foo() -> Bar<FOO<impl Trait>>` support
ImplTraitContext::Disallowed(ImplTraitPosition::Path),
None,
);
@ -2136,19 +2136,18 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
};
let maybe_res =
self.resolver.get_partial_res(expr.id).and_then(|partial_res| partial_res.full_res());
// FIXME(min_generic_const_args): we only allow one-segment const paths for now
if let ExprKind::Path(None, path) = &expr.kind
&& path.is_potential_trivial_const_arg()
if let ExprKind::Path(qself, path) = &expr.kind
&& path.is_potential_trivial_const_arg(tcx.features().min_generic_const_args())
&& (tcx.features().min_generic_const_args()
|| matches!(maybe_res, Some(Res::Def(DefKind::ConstParam, _))))
{
let qpath = self.lower_qpath(
expr.id,
&None,
qself,
path,
ParamMode::Optional,
AllowReturnTypeNotation::No,
// FIXME(min_generic_const_args): update for `fn foo() -> Bar<FOO<impl Trait>>` support
// FIXME(mgca): update for `fn foo() -> Bar<FOO<impl Trait>>` support
ImplTraitContext::Disallowed(ImplTraitPosition::Path),
None,
);