Rollup merge of #125792 - compiler-errors:dont-drop-upcast-cand, r=lcnr

Don't drop `Unsize` candidate in intercrate mode

Fixes #125767
This commit is contained in:
Matthias Krüger 2024-06-05 18:21:09 +02:00 committed by GitHub
commit e1745122ae
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3 changed files with 30 additions and 0 deletions

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@ -921,6 +921,12 @@ fn need_migrate_deref_output_trait_object(
param_env: ty::ParamEnv<'tcx>,
cause: &ObligationCause<'tcx>,
) -> Option<ty::PolyExistentialTraitRef<'tcx>> {
// Don't drop any candidates in intercrate mode, as it's incomplete.
// (Not that it matters, since `Unsize` is not a stable trait.)
if self.infcx.intercrate {
return None;
}
let tcx = self.tcx();
if tcx.features().trait_upcasting {
return None;

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@ -0,0 +1,13 @@
#![feature(unsize)]
use std::marker::Unsize;
use std::ops::Deref;
trait Foo: Bar {}
trait Bar {}
impl<T> Bar for T where dyn Foo: Unsize<dyn Bar> {}
impl Bar for () {}
//~^ ERROR conflicting implementations of trait `Bar` for type `()`
fn main() {}

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@ -0,0 +1,11 @@
error[E0119]: conflicting implementations of trait `Bar` for type `()`
--> $DIR/dont-drop-upcast-candidate.rs:10:1
|
LL | impl<T> Bar for T where dyn Foo: Unsize<dyn Bar> {}
| ------------------------------------------------ first implementation here
LL | impl Bar for () {}
| ^^^^^^^^^^^^^^^ conflicting implementation for `()`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0119`.