Add test for issue rust-lang#79636

Author: marmeladema

src/test/ui/generic-associated-types/issue-79636-1.rs

@@ -0,0 +1,24 @@
+#![allow(incomplete_features)]
+#![feature(generic_associated_types)]
+
+trait Monad {
+    type Unwrapped;
+    type Wrapped<B>;
+         //~^ ERROR: missing generics for associated type `Monad::Wrapped`
+
+    fn bind<B, F>(self, f: F) -> Self::Wrapped<B> {
+        todo!()
+    }
+}
+
+fn join<MOuter, MInner, A>(outer: MOuter) -> MOuter::Wrapped<A>
+where
+    MOuter: Monad<Unwrapped = MInner>,
+    MInner: Monad<Unwrapped = A, Wrapped = MOuter::Wrapped<A>>,
+{
+    outer.bind(|inner| inner)
+}
+
+fn main() {
+    assert_eq!(join(Some(Some(true))), Some(true));
+}

src/test/ui/generic-associated-types/issue-79636-1.stderr

@@ -0,0 +1,19 @@
+error[E0107]: missing generics for associated type `Monad::Wrapped`
+  --> $DIR/issue-79636-1.rs:6:10
+   |
+LL |     type Wrapped<B>;
+   |          ^^^^^^^ expected 1 type argument
+   |
+note: associated type defined here, with 1 type parameter: `B`
+  --> $DIR/issue-79636-1.rs:6:10
+   |
+LL |     type Wrapped<B>;
+   |          ^^^^^^^ -
+help: use angle brackets to add missing type argument
+   |
+LL |     type Wrapped<B><B>;
+   |                 ^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0107`.

src/test/ui/generic-associated-types/issue-79636-2.rs

@@ -0,0 +1,18 @@
+#![allow(incomplete_features)]
+#![feature(generic_associated_types)]
+
+trait SomeTrait {
+    type Wrapped<A>: SomeTrait;
+         //~^ ERROR: missing generics for associated type `SomeTrait::Wrapped`
+
+    fn f() -> ();
+}
+
+fn program<W>() -> ()
+where
+    W: SomeTrait<Wrapped = W>,
+{
+    return W::f();
+}
+
+fn main() {}

src/test/ui/generic-associated-types/issue-79636-2.stderr

@@ -0,0 +1,19 @@
+error[E0107]: missing generics for associated type `SomeTrait::Wrapped`
+  --> $DIR/issue-79636-2.rs:5:10
+   |
+LL |     type Wrapped<A>: SomeTrait;
+   |          ^^^^^^^ expected 1 type argument
+   |
+note: associated type defined here, with 1 type parameter: `A`
+  --> $DIR/issue-79636-2.rs:5:10
+   |
+LL |     type Wrapped<A>: SomeTrait;
+   |          ^^^^^^^ -
+help: use angle brackets to add missing type argument
+   |
+LL |     type Wrapped<A><A>: SomeTrait;
+   |                 ^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0107`.