Add some more tests

tests/ui/type-alias-impl-trait/constrain_in_projection.rs

@@ -0,0 +1,27 @@
+//! Check that projections will constrain opaque types while looking for
+//! matching impls.
+
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@check-pass
+
+#![feature(type_alias_impl_trait)]
+
+struct Foo;
+
+type Bar = impl Sized;
+
+trait Trait<T> {
+    type Assoc: Default;
+}
+
+impl Trait<()> for Foo {
+    type Assoc = u32;
+}
+
+fn bop(_: Bar) {
+    let x = <Foo as Trait<Bar>>::Assoc::default();
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/constrain_in_projection2.current.stderr

@@ -0,0 +1,19 @@
+error[E0283]: type annotations needed: cannot satisfy `Foo: Trait<Bar>`
+  --> $DIR/constrain_in_projection2.rs:27:14
+   |
+LL |     let x = <Foo as Trait<Bar>>::Assoc::default();
+   |              ^^^ help: use the fully qualified path to an implementation: `<Type as Trait>::Assoc`
+   |
+note: multiple `impl`s satisfying `Foo: Trait<Bar>` found
+  --> $DIR/constrain_in_projection2.rs:18:1
+   |
+LL | impl Trait<()> for Foo {
+   | ^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | impl Trait<u32> for Foo {
+   | ^^^^^^^^^^^^^^^^^^^^^^^
+   = note: associated types cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.

tests/ui/type-alias-impl-trait/constrain_in_projection2.next.stderr

@@ -0,0 +1,19 @@
+error[E0283]: type annotations needed: cannot satisfy `Foo: Trait<Bar>`
+  --> $DIR/constrain_in_projection2.rs:27:14
+   |
+LL |     let x = <Foo as Trait<Bar>>::Assoc::default();
+   |              ^^^ help: use the fully qualified path to an implementation: `<Type as Trait>::Assoc`
+   |
+note: multiple `impl`s satisfying `Foo: Trait<Bar>` found
+  --> $DIR/constrain_in_projection2.rs:18:1
+   |
+LL | impl Trait<()> for Foo {
+   | ^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | impl Trait<u32> for Foo {
+   | ^^^^^^^^^^^^^^^^^^^^^^^
+   = note: associated types cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.

tests/ui/type-alias-impl-trait/constrain_in_projection2.rs

@@ -0,0 +1,31 @@
+//! Check that projections will constrain opaque types while looking for
+//! matching impls and error if ambiguous.
+
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+#![feature(type_alias_impl_trait)]
+
+struct Foo;
+
+type Bar = impl Sized;
+
+trait Trait<T> {
+    type Assoc: Default;
+}
+
+impl Trait<()> for Foo {
+    type Assoc = u32;
+}
+
+impl Trait<u32> for Foo {
+    type Assoc = u32;
+}
+
+fn bop(_: Bar) {
+    let x = <Foo as Trait<Bar>>::Assoc::default();
+    //~^ ERROR: cannot satisfy `Foo: Trait<Bar>`
+}
+
+fn main() {}