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Function item should not be used as const arg #157962

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Function item should not be used as const arg #157962

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b4dbd51
add test when function item is used as const arg
Shourya742 Jun 16, 2026
dd56e6b
Previously both free functions and associated functions creates a FnD…
Shourya742 Jun 16, 2026
f227e79
Remove crashtest and mention the issue in the ui test
Shourya742 Jun 17, 2026
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7 changes: 6 additions & 1 deletion compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2791,8 +2791,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
Res::Def(DefKind::Static { .. }, _) => {
span_bug!(span, "use of bare `static` ConstArgKind::Path's not yet supported")
}
Res::Def(DefKind::AssocFn, _) => {
let guar =
self.dcx().span_err(span, "function items cannot be used as const arguments");
Const::new_error(tcx, guar)
}
// FIXME(const_generics): create real const to allow fn items as const paths
Res::Def(DefKind::Fn | DefKind::AssocFn, did) => {
Res::Def(DefKind::Fn, did) => {
Comment on lines +2794 to +2800

@Shourya742 Shourya742 Jun 16, 2026 •
edited by rustbot
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Previous both free function and associated function, where lowering to zero_sized fn def which would later emit diagnostics, but to lower the assoc it required the parent trait. This now emits an error, instead of lowering.

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self.dcx().span_delayed_bug(span, "function items cannot be used as const args");
let args = self.lower_generic_args_of_path_segment(
span,
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5 changes: 0 additions & 5 deletions tests/crashes/138088.rs
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This file was deleted.

10 changes: 10 additions & 0 deletions tests/ui/const-generics/mgca/trait-assoc-fn-as-const-arg.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
#![feature(min_generic_const_args)]

// Regression test for #138088. assoc functions cannot be lowered as const
// args, and this should emit a regular diagnostic instead of ICEing.
trait Bar {
fn x(&self) -> [i32; Bar::x];
//~^ ERROR function items cannot be used as const arguments
}

fn main() {}
8 changes: 8 additions & 0 deletions tests/ui/const-generics/mgca/trait-assoc-fn-as-const-arg.stderr
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@@ -0,0 +1,8 @@
error: function items cannot be used as const arguments
--> $DIR/trait-assoc-fn-as-const-arg.rs:6:26
|
LL | fn x(&self) -> [i32; Bar::x];
| ^^^^^^

error: aborting due to 1 previous error

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