Add regression tests for #101903

tests/ui/type-alias-impl-trait/tait-in-function-return-type-issue-101903-fixed.rs

@@ -0,0 +1,26 @@
+//@ check-pass
+
+#![feature(type_alias_impl_trait)]
+#![allow(dead_code)]
+
+trait Duh {}
+
+impl Duh for i32 {}
+
+trait Trait {
+    type Assoc: Duh;
+}
+
+impl<R: Duh, F: FnMut() -> R> Trait for F {
+    type Assoc = R;
+}
+
+type Sendable = impl Send + Duh;
+
+type Foo = impl Trait<Assoc = Sendable>;
+
+fn foo() -> Foo {
+    || 42
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/tait-in-function-return-type-issue-101903.rs

@@ -0,0 +1,29 @@
+//@ check-pass
+
+// See https://doc.rust-lang.org/1.77.0/nightly-rustc/rustc_lint/opaque_hidden_inferred_bound/static.OPAQUE_HIDDEN_INFERRED_BOUND.html#example
+
+#![feature(type_alias_impl_trait)]
+#![allow(dead_code)]
+
+trait Duh {}
+
+impl Duh for i32 {}
+
+trait Trait {
+    type Assoc: Duh;
+}
+
+impl<R: Duh, F: FnMut() -> R> Trait for F {
+    type Assoc = R;
+}
+
+type Sendable = impl Send;
+
+type Foo = impl Trait<Assoc = Sendable>;
+                   //~^ WARNING opaque type `Foo` does not satisfy its associated type bounds
+
+fn foo() -> Foo {
+    || 42
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/tait-in-function-return-type-issue-101903.stderr

@@ -0,0 +1,13 @@
+warning: opaque type `Foo` does not satisfy its associated type bounds
+  --> $DIR/tait-in-function-return-type-issue-101903.rs:22:23
+   |
+LL |     type Assoc: Duh;
+   |                 --- this associated type bound is unsatisfied for `Sendable`
+...
+LL | type Foo = impl Trait<Assoc = Sendable>;
+   |                       ^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(opaque_hidden_inferred_bound)]` on by default
+
+warning: 1 warning emitted
+