Add test for #65774

Closes #65774

Author: jonas-schievink

src/test/ui/associated-types/issue-65774-1.rs

@@ -0,0 +1,57 @@
+#![feature(associated_type_defaults)]
+
+trait MyDisplay { fn method(&self) { } }
+
+impl<'a, T: MyDisplay> MyDisplay for &'a mut T { }
+
+struct T;
+
+trait MPU {
+    type MpuConfig: MyDisplay = T;
+    //~^ ERROR the trait bound `T: MyDisplay` is not satisfied
+}
+
+struct S;
+
+impl MPU for S { }
+//~^ ERROR the trait bound `T: MyDisplay` is not satisfied
+
+trait MyWrite {
+    fn my_write(&self, _: &dyn MyDisplay) { }
+}
+
+trait ProcessType {
+    fn process_detail_fmt(&self, _: &mut dyn MyWrite);
+}
+
+struct Process;
+
+impl ProcessType for Process {
+    fn process_detail_fmt(&self, writer: &mut dyn MyWrite)
+    {
+
+        let mut val: Option<<S as MPU>::MpuConfig> = None;
+        let valref: &mut <S as MPU>::MpuConfig = val.as_mut().unwrap();
+
+        // // This causes a different ICE (but its similar if you squint right):
+        // //
+        // // `Unimplemented` selecting `Binder(<T as MyDisplay>)` during codegen
+        //
+        // writer.my_write(valref)
+
+        // This one causes the ICE:
+        // FulfillmentError(Obligation(predicate=Binder(TraitPredicate(<T as MyDisplay>)), depth=1),Unimplemented)
+        let closure = |config: &mut <S as MPU>::MpuConfig| writer.my_write(&config);
+        closure(valref);
+    }
+}
+
+fn create() -> &'static dyn ProcessType {
+    let input: Option<&mut Process> = None;
+    let process: &mut Process = input.unwrap();
+    process
+}
+
+pub fn main() {
+    create();
+}

src/test/ui/associated-types/issue-65774-1.stderr

@@ -0,0 +1,17 @@
+error[E0277]: the trait bound `T: MyDisplay` is not satisfied
+  --> $DIR/issue-65774-1.rs:10:21
+   |
+LL | trait MPU {
+   | --------- required by `MPU`
+LL |     type MpuConfig: MyDisplay = T;
+   |                     ^^^^^^^^^ the trait `MyDisplay` is not implemented for `T`
+
+error[E0277]: the trait bound `T: MyDisplay` is not satisfied
+  --> $DIR/issue-65774-1.rs:16:6
+   |
+LL | impl MPU for S { }
+   |      ^^^ the trait `MyDisplay` is not implemented for `T`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/associated-types/issue-65774-2.rs

@@ -0,0 +1,57 @@
+#![feature(associated_type_defaults)]
+
+trait MyDisplay { fn method(&self) { } }
+
+impl<'a, T: MyDisplay> MyDisplay for &'a mut T { }
+
+struct T;
+
+trait MPU {
+    type MpuConfig: MyDisplay = T;
+    //~^ ERROR the trait bound `T: MyDisplay` is not satisfied
+}
+
+struct S;
+
+impl MPU for S { }
+//~^ ERROR the trait bound `T: MyDisplay` is not satisfied
+
+trait MyWrite {
+    fn my_write(&self, _: &dyn MyDisplay) { }
+}
+
+trait ProcessType {
+    fn process_detail_fmt(&self, _: &mut dyn MyWrite);
+}
+
+struct Process;
+
+impl ProcessType for Process {
+    fn process_detail_fmt(&self, writer: &mut dyn MyWrite)
+    {
+
+        let mut val: Option<<S as MPU>::MpuConfig> = None;
+        let valref: &mut <S as MPU>::MpuConfig = val.as_mut().unwrap();
+
+        // // This causes a different ICE (but its similar if you squint right):
+        // //
+        // // `Unimplemented` selecting `Binder(<T as MyDisplay>)` during codegen
+        //
+        writer.my_write(valref)
+
+        // This one causes the ICE:
+        // FulfillmentError(Obligation(predicate=Binder(TraitPredicate(<T as MyDisplay>)), depth=1),Unimplemented)
+        /*let closure = |config: &mut <S as MPU>::MpuConfig| writer.my_write(&config);
+        closure(valref);*/
+    }
+}
+
+fn create() -> &'static dyn ProcessType {
+    let input: Option<&mut Process> = None;
+    let process: &mut Process = input.unwrap();
+    process
+}
+
+pub fn main() {
+    create();
+}

src/test/ui/associated-types/issue-65774-2.stderr

@@ -0,0 +1,17 @@
+error[E0277]: the trait bound `T: MyDisplay` is not satisfied
+  --> $DIR/issue-65774-2.rs:10:21
+   |
+LL | trait MPU {
+   | --------- required by `MPU`
+LL |     type MpuConfig: MyDisplay = T;
+   |                     ^^^^^^^^^ the trait `MyDisplay` is not implemented for `T`
+
+error[E0277]: the trait bound `T: MyDisplay` is not satisfied
+  --> $DIR/issue-65774-2.rs:16:6
+   |
+LL | impl MPU for S { }
+   |      ^^^ the trait `MyDisplay` is not implemented for `T`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.