Rollup merge of #154359 - TaKO8Ki:fix-154189-generalize-associated-type-alias, r=Kivooeo

Add regression test for #154189

Fixes #154189

Author: JonathanBrouwer

tests/ui/coherence/generalize-associated-type-alias.rs

@@ -0,0 +1,22 @@
+// Regression test for https://github.com/rust-lang/rust/issues/154189.
+#![feature(unboxed_closures)]
+
+trait ToUnit<'a> {
+    type Unit;
+}
+
+impl ToUnit<'_> for *const u32 {
+    type Unit = ();
+}
+
+trait Overlap<T> {}
+
+type Assoc<'a, T> = <*const T as ToUnit<'a>>::Unit;
+
+impl<T> Overlap<T> for T {}
+
+impl<'a, T> Overlap<(&'a (), Assoc<'a, T>)> for T {}
+//~^ ERROR the trait bound `*const T: ToUnit<'a>` is not satisfied
+//~| ERROR the trait bound `T: Overlap<(&'a (), _)>` is not satisfied
+
+fn main() {}

tests/ui/coherence/generalize-associated-type-alias.stderr

@@ -0,0 +1,28 @@
+error[E0277]: the trait bound `*const T: ToUnit<'a>` is not satisfied
+  --> $DIR/generalize-associated-type-alias.rs:18:13
+   |
+LL | impl<'a, T> Overlap<(&'a (), Assoc<'a, T>)> for T {}
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `ToUnit<'a>` is not implemented for `*const T`
+   |
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | impl<'a, T> Overlap<(&'a (), Assoc<'a, T>)> for T where *const T: ToUnit<'a> {}
+   |                                                   ++++++++++++++++++++++++++
+
+error[E0277]: the trait bound `T: Overlap<(&'a (), _)>` is not satisfied
+  --> $DIR/generalize-associated-type-alias.rs:18:49
+   |
+LL | impl<'a, T> Overlap<(&'a (), Assoc<'a, T>)> for T {}
+   |                                                 ^ the trait `Overlap<(&'a (), _)>` is not implemented for `T`
+   |
+help: the trait `Overlap<(&'a (), _)>` is not implemented for `T`
+      but trait `Overlap<(&(), ())>` is implemented for `u32`
+  --> $DIR/generalize-associated-type-alias.rs:18:1
+   |
+LL | impl<'a, T> Overlap<(&'a (), Assoc<'a, T>)> for T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = help: for that trait implementation, expected `u32`, found `T`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.