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Allow constraining opaque types during auto trait casting

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This commit is contained in:
Oli Scherer 2024-05-27 10:44:35 +00:00
parent cbadf786bc
commit 4a86ef6f4c
5 changed files with 30 additions and 32 deletions
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2
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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@ -1161,7 +1161,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let InferOk { mut obligations, .. } = self
.infcx
.at(&obligation.cause, obligation.param_env)
.sup(DefineOpaqueTypes::No, target, source_trait)
.sup(DefineOpaqueTypes::Yes, target, source_trait)
.map_err(|_| Unimplemented)?;
// Register one obligation for 'a: 'b.

4
tests/ui/impl-trait/trait_upcasting.rs
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@ -1,5 +1,7 @@
//! Test that we allow unsizing `Trait<Concrete>` to `Trait<Opaque>` and vice versa
//@ check-pass
trait Trait<T> {}
impl<T, U> Trait<T> for U {}
@ -8,7 +10,6 @@ fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
if false {
let x = hello();
let _: &'static dyn Trait<()> = x;
//~^ ERROR: mismatched types
}
todo!()
}
@ -18,7 +19,6 @@ fn bye() -> &'static dyn Trait<impl Sized> {
let mut x = bye();
let y: &'static (dyn Trait<()> + Send) = &();
x = y;
//~^ ERROR: mismatched types
}
todo!()
}

29
tests/ui/impl-trait/trait_upcasting.stderr
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@ -1,29 +0,0 @@
error[E0308]: mismatched types
--> $DIR/trait_upcasting.rs:10:41
|
LL | fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
| ---------- the found opaque type
...
LL | let _: &'static dyn Trait<()> = x;
| ---------------------- ^ expected trait `Trait<()>`, found trait `Trait<impl Sized> + Send`
| |
| expected due to this
|
= note: expected reference `&'static (dyn Trait<()> + 'static)`
found reference `&dyn Trait<impl Sized> + Send`
error[E0308]: mismatched types
--> $DIR/trait_upcasting.rs:20:13
|
LL | fn bye() -> &'static dyn Trait<impl Sized> {
| ---------- the expected opaque type
...
LL | x = y;
| ^ expected trait `Trait<impl Sized>`, found trait `Trait<()> + Send`
|
= note: expected reference `&dyn Trait<impl Sized>`
found reference `&'static (dyn Trait<()> + Send + 'static)`
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0308`.

18
tests/ui/impl-trait/trait_upcasting_reference_mismatch.rs Normal file
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@ -0,0 +1,18 @@
//! Show an uninformative diagnostic that we could possibly improve in the future
trait Trait<T> {}
impl<T, U> Trait<T> for U {}
fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
//~^ ERROR: type annotations needed
if false {
let x = hello();
let _: &'static dyn Trait<()> = &x;
//^ Note the extra `&`, paired with the blanket impl causing
// `impl Sized` to never get a hidden type registered.
}
todo!()
}
fn main() {}

9
tests/ui/impl-trait/trait_upcasting_reference_mismatch.stderr Normal file
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@ -0,0 +1,9 @@
error[E0282]: type annotations needed
--> $DIR/trait_upcasting_reference_mismatch.rs:7:35
|
LL | fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
| ^^^^^^^^^^ cannot infer type
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0282`.