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Rollup merge of rust-lang#122942 - Luv-Ray:master, r=lcnr
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Add test in higher ranked subtype

I'm a beginner in this repository, and there are some things I'm not sure about:

- Is it okay that there is a warning:
```
rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, '^0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit) }
```
- Is it okay that there are two duplicate errors in the same line?
- Did I put the test in the right place?

Any suggestions would be appreciated.

Fixes rust-lang#121649
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matthiaskrgr authored and RenjiSann committed Mar 25, 2024
2 parents e896fd1 + e9e9f7f commit 819e891
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17 changes: 17 additions & 0 deletions tests/ui/higher-ranked/structually-relate-aliases.rs
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@@ -0,0 +1,17 @@
// regression test for issue #121649.

trait ToUnit<'a> {
type Unit;
}

trait Overlap<T> {}

type Assoc<'a, T> = <T as ToUnit<'a>>::Unit;

impl<T> Overlap<T> for T {}

impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
//~^ ERROR 13:17: 13:49: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied [E0277]
//~| ERROR 13:36: 13:48: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied [E0277]

fn main() {}
27 changes: 27 additions & 0 deletions tests/ui/higher-ranked/structually-relate-aliases.stderr
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WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, '^0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit) }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, !2_0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit) }
error[E0277]: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied
--> $DIR/structually-relate-aliases.rs:13:36
|
LL | impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
| ^^^^^^^^^^^^ the trait `for<'a> ToUnit<'a>` is not implemented for `T`
|
help: consider restricting type parameter `T`
|
LL | impl<T: for<'a> ToUnit<'a>> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
| ++++++++++++++++++++

error[E0277]: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied
--> $DIR/structually-relate-aliases.rs:13:17
|
LL | impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> ToUnit<'a>` is not implemented for `T`
|
help: consider restricting type parameter `T`
|
LL | impl<T: for<'a> ToUnit<'a>> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
| ++++++++++++++++++++

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0277`.

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