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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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21
compiler/rustc_passes/src/check_attr.rs
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@ -14,6 +14,7 @@ use rustc_attr_parsing::{AttributeKind, ReprAttr, find_attr};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{Applicability, DiagCtxtHandle, IntoDiagArg, MultiSpan, StashKey};
use rustc_feature::{AttributeDuplicates, AttributeType, BUILTIN_ATTRIBUTE_MAP, BuiltinAttribute};
use rustc_hir::def::DefKind;
use rustc_hir::def_id::LocalModDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{
@ -257,6 +258,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
[sym::coroutine, ..] => {
self.check_coroutine(attr, target);
}
[sym::type_const, ..] => {
self.check_type_const(hir_id,attr, target);
}
[sym::linkage, ..] => self.check_linkage(attr, span, target),
[sym::rustc_pub_transparent, ..] => self.check_rustc_pub_transparent(attr.span(), span, attrs),
[
@ -2519,6 +2523,23 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
}
}
fn check_type_const(&self, hir_id: HirId, attr: &Attribute, target: Target) {
let tcx = self.tcx;
if target == Target::AssocConst
&& let parent = tcx.parent(hir_id.expect_owner().to_def_id())
&& self.tcx.def_kind(parent) == DefKind::Trait
{
return;
} else {
self.dcx()
.struct_span_err(
attr.span(),
"`#[type_const]` must only be applied to trait associated constants",
)
.emit();
}
}
fn check_linkage(&self, attr: &Attribute, span: Span, target: Target) {
match target {
Target::Fn