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Preserve constness in trait objects up to hir ty lowering #143927

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Merged
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Jul 15, 2025
+27 −3
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Preserve constness in trait objects up to hir ty lowering #143927

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2 changes: 1 addition & 1 deletion compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
} = self.lower_poly_trait_ref(
&trait_bound.trait_ref,
trait_bound.span,
hir::BoundConstness::Never,
trait_bound.modifiers.constness,
hir::BoundPolarity::Positive,
dummy_self,
&mut user_written_bounds,
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2 changes: 2 additions & 0 deletions tests/ui/traits/const-traits/const-trait-bounds-trait-objects.rs
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Expand Up @@ -14,5 +14,7 @@ fn main() {
trait NonConst {}
const fn handle(_: &dyn const NonConst) {}
//~^ ERROR const trait bounds are not allowed in trait object types
//~| ERROR `const` can only be applied to `#[const_trait]` traits
const fn take(_: &dyn [const] NonConst) {}
//~^ ERROR `[const]` is not allowed here
//~| ERROR `[const]` can only be applied to `#[const_trait]` traits
26 changes: 24 additions & 2 deletions tests/ui/traits/const-traits/const-trait-bounds-trait-objects.stderr
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Expand Up @@ -19,12 +19,34 @@ LL | const fn handle(_: &dyn const NonConst) {}
| ^^^^^^^^^^^^^^

error: `[const]` is not allowed here
--> $DIR/const-trait-bounds-trait-objects.rs:17:23
--> $DIR/const-trait-bounds-trait-objects.rs:18:23
|
LL | const fn take(_: &dyn [const] NonConst) {}
| ^^^^^^^
|
= note: trait objects cannot have `[const]` trait bounds

error: aborting due to 4 previous errors
error: `const` can only be applied to `#[const_trait]` traits
--> $DIR/const-trait-bounds-trait-objects.rs:15:25
|
LL | const fn handle(_: &dyn const NonConst) {}
| ^^^^^ can't be applied to `NonConst`
|
help: mark `NonConst` as `#[const_trait]` to allow it to have `const` implementations
|
LL | #[const_trait] trait NonConst {}
| ++++++++++++++

error: `[const]` can only be applied to `#[const_trait]` traits
--> $DIR/const-trait-bounds-trait-objects.rs:18:23
|
LL | const fn take(_: &dyn [const] NonConst) {}
| ^^^^^^^ can't be applied to `NonConst`
|
help: mark `NonConst` as `#[const_trait]` to allow it to have `const` implementations
|
LL | #[const_trait] trait NonConst {}
| ++++++++++++++

error: aborting due to 6 previous errors

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