Test recursive TAIT declarations

Author: oli-obk

src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.rs

@@ -0,0 +1,29 @@
+#![feature(type_alias_impl_trait)]
+
+mod a {
+    type Foo = impl PartialEq<(Foo, i32)>;
+    //~^ ERROR could not find defining uses
+
+    struct Bar;
+
+    impl PartialEq<(Bar, i32)> for Bar {
+        fn eq(&self, _other: &(Foo, i32)) -> bool {
+            true
+        }
+    }
+}
+
+mod b {
+    type Foo = impl PartialEq<(Foo, i32)>;
+    //~^ ERROR could not find defining uses
+
+    struct Bar;
+
+    impl PartialEq<(Foo, i32)> for Bar {
+        fn eq(&self, _other: &(Bar, i32)) -> bool {
+            true
+        }
+    }
+}
+
+fn main() {}

src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr

@@ -0,0 +1,14 @@
+error: could not find defining uses
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:4:16
+   |
+LL |     type Foo = impl PartialEq<(Foo, i32)>;
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: could not find defining uses
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:17:16
+   |
+LL |     type Foo = impl PartialEq<(Foo, i32)>;
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+

src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration.rs

@@ -0,0 +1,37 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+
+mod direct {
+    type Foo = impl PartialEq<(Foo, i32)>;
+
+    struct Bar;
+
+    impl PartialEq<(Foo, i32)> for Bar {
+        fn eq(&self, _other: &(Foo, i32)) -> bool {
+            true
+        }
+    }
+
+    fn foo() -> Foo {
+        Bar
+    }
+}
+
+mod indirect {
+    type Foo = impl PartialEq<(Foo, i32)>;
+
+    struct Bar;
+
+    impl PartialEq<(Bar, i32)> for Bar {
+        fn eq(&self, _other: &(Bar, i32)) -> bool {
+            true
+        }
+    }
+
+    fn foo() -> Foo {
+        Bar
+    }
+}
+
+fn main() {}