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Reject static item as direct const generic arg #158479

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Reject static item as direct const generic arg #158479

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c6ee50d
Add test for two cases 1. const argument expression 2. const argument…
Shourya742 Jun 27, 2026
c5de45f
make sure to emite ConstKindArg::Error while AST lowering itselff for…
Shourya742 Jun 27, 2026
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11 changes: 10 additions & 1 deletion compiler/rustc_ast_lowering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2549,7 +2549,10 @@ impl<'hir> LoweringContext<'_, 'hir> {

let is_trivial_path = path.is_potential_trivial_const_arg()
&& matches!(res, Res::Def(DefKind::ConstParam, _));
let ct_kind = if is_trivial_path || tcx.features().min_generic_const_args() {
let ct_kind = if matches!(res, Res::Def(DefKind::Static { .. }, _)) {
let msg = "complex const arguments must be placed inside of a `const` block";
hir::ConstArgKind::Error(self.dcx().struct_span_err(span, msg).emit())
} else if is_trivial_path || tcx.features().min_generic_const_args() {
let qpath = self.lower_qpath(

@BoxyUwU BoxyUwU Jul 8, 2026 •
edited by rustbot
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cc @khyperia i don't think we handled this codepath in your PR overhauling ast lowering for mgca. we should probably be checking can_lower_to_direct_const_arg here and then also reusing the lower_expr_to_direct logic here? though it would really just be the path arms right now but still... seems nice for consistency/sharing logic 🤔

unrelated to this PR, just something i realised while reading this

View changes since the review

@khyperia khyperia Jul 8, 2026

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yus, the logic here happens to be identical even with the syntax flip PR, but, it's a very wishy-washy "happens to be correct" and you're absolutely right that these should share a codepath so they don't accidentally diverge

ty_id,
&None,
Expand Down Expand Up @@ -2677,6 +2680,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
ConstArg { hir_id: self.next_id(), kind: hir::ConstArgKind::Tup(exprs), span }
}
ExprKind::Path(qself, path) => {
if let Some(Res::Def(DefKind::Static { .. }, _)) =
self.get_partial_res(expr.id).and_then(|partial_res| partial_res.full_res())
{
return overly_complex_const(self);
}

let qpath = self.lower_qpath(
expr.id,
qself,
Expand Down
18 changes: 18 additions & 0 deletions tests/ui/const-generics/mgca/static-const-arg.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
// Regression test for #132986.
// FIXME(min_generic_const_args): using statics as direct const arguments should error instead of
// ICEing until const eval can evaluate statics to valtrees for const generics.

#![feature(min_generic_const_args)]
#![allow(incomplete_features)]

static A: u32 = 0;

struct Foo<const N: u32>;

const _: Foo<{ A }> = Foo;
//~^ ERROR complex const arguments must be placed inside of a `const` block

const _: Foo<A> = Foo;
//~^ ERROR complex const arguments must be placed inside of a `const` block

fn main() {}
14 changes: 14 additions & 0 deletions tests/ui/const-generics/mgca/static-const-arg.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
error: complex const arguments must be placed inside of a `const` block
--> $DIR/static-const-arg.rs:12:16
|
LL | const _: Foo<{ A }> = Foo;
| ^

error: complex const arguments must be placed inside of a `const` block
--> $DIR/static-const-arg.rs:15:14
|
LL | const _: Foo<A> = Foo;
| ^

error: aborting due to 2 previous errors

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