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Distinguish error message for #[diagnostic::on_const] on const trait impls #152054

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Merged
rust-bors merged 1 commit into from
Feb 4, 2026
Merged

Distinguish error message for #[diagnostic::on_const] on const trait impls #152054

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4 changes: 4 additions & 0 deletions compiler/rustc_passes/messages.ftl
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Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,10 @@ passes_deprecated_annotation_has_no_effect =
passes_deprecated_attribute =
deprecated attribute must be paired with either stable or unstable attribute
passes_diagnostic_diagnostic_on_const_only_for_non_const_trait_impls =
`#[diagnostic::on_const]` can only be applied to non-const trait impls
.label = this is a const trait impl
passes_diagnostic_diagnostic_on_const_only_for_trait_impls =
`#[diagnostic::on_const]` can only be applied to trait impls
.label = not a trait impl
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18 changes: 17 additions & 1 deletion compiler/rustc_passes/src/check_attr.rs
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Expand Up @@ -67,6 +67,13 @@ struct DiagnosticOnConstOnlyForTraitImpls {
item_span: Span,
}

#[derive(LintDiagnostic)]
#[diag(passes_diagnostic_diagnostic_on_const_only_for_non_const_trait_impls)]
struct DiagnosticOnConstOnlyForNonConstTraitImpls {
#[label]
item_span: Span,
}

fn target_from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
match impl_item.kind {
hir::ImplItemKind::Const(..) => Target::AssocConst,
Expand Down Expand Up @@ -629,7 +636,16 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
if target == (Target::Impl { of_trait: true }) {
match item.unwrap() {
ItemLike::Item(it) => match it.expect_impl().constness {
Constness::Const => {}
Constness::Const => {
let item_span = self.tcx.hir_span(hir_id);
self.tcx.emit_node_span_lint(
MISPLACED_DIAGNOSTIC_ATTRIBUTES,
hir_id,
attr_span,
DiagnosticOnConstOnlyForNonConstTraitImpls { item_span },
);
return;
}
Constness::NotConst => return,
},
ItemLike::ForeignItem => {}
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2 changes: 1 addition & 1 deletion tests/ui/diagnostic_namespace/on_const/misplaced_attr.rs
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Expand Up @@ -6,7 +6,7 @@
pub struct Foo;

#[diagnostic::on_const(message = "tadaa", note = "boing")]
//~^ ERROR: `#[diagnostic::on_const]` can only be applied to trait impls
//~^ ERROR: `#[diagnostic::on_const]` can only be applied to non-const trait impls
impl const PartialEq for Foo {
fn eq(&self, _other: &Foo) -> bool {
true
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4 changes: 2 additions & 2 deletions tests/ui/diagnostic_namespace/on_const/misplaced_attr.stderr
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Expand Up @@ -13,14 +13,14 @@ note: the lint level is defined here
LL | #![deny(misplaced_diagnostic_attributes)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: `#[diagnostic::on_const]` can only be applied to trait impls
error: `#[diagnostic::on_const]` can only be applied to non-const trait impls
--> $DIR/misplaced_attr.rs:8:1
|
LL | #[diagnostic::on_const(message = "tadaa", note = "boing")]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL |
LL | impl const PartialEq for Foo {
| ---------------------------- not a trait impl
| ---------------------------- this is a const trait impl

error: `#[diagnostic::on_const]` can only be applied to trait impls
--> $DIR/misplaced_attr.rs:16:1
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