3 files changed, 95 insertions, 1 deletions
diff --git a/tests/ui/implied_bounds_in_impls.fixed b/tests/ui/implied_bounds_in_impls.fixed
index fa117aaddcd..18f29e900c1 100644
--- a/tests/ui/implied_bounds_in_impls.fixed
+++ b/tests/ui/implied_bounds_in_impls.fixed
@@ -121,4 +121,33 @@ mod issue11435 {
     fn f3() -> impl Trait4<i8, X = i32, Y = i128> {}
 }
 
+fn issue11880() {
+    trait X {
+        type T;
+        type U;
+    }
+    trait Y: X {
+        type T;
+        type V;
+    }
+    impl X for () {
+        type T = i32;
+        type U = String;
+    }
+    impl Y for () {
+        type T = u32;
+        type V = Vec<u8>;
+    }
+
+    // Can't constrain `X::T` through `Y`
+    fn f() -> impl X<T = i32> + Y {}
+    fn f2() -> impl X<T = i32> + Y<T = u32> {}
+
+    // X::T is never constrained in the first place, so it can be omitted
+    // and left unconstrained
+    fn f3() -> impl Y {}
+    fn f4() -> impl Y<T = u32> {}
+    fn f5() -> impl Y<T = u32, U = String> {}
+}
+
 fn main() {}
diff --git a/tests/ui/implied_bounds_in_impls.rs b/tests/ui/implied_bounds_in_impls.rs
index c96aac151a7..b7951e7dfba 100644
--- a/tests/ui/implied_bounds_in_impls.rs
+++ b/tests/ui/implied_bounds_in_impls.rs
@@ -121,4 +121,33 @@ mod issue11435 {
     fn f3() -> impl Trait3<i8, i16, i64, X = i32, Y = i128> + Trait4<i8, X = i32> {}
 }
 
+fn issue11880() {
+    trait X {
+        type T;
+        type U;
+    }
+    trait Y: X {
+        type T;
+        type V;
+    }
+    impl X for () {
+        type T = i32;
+        type U = String;
+    }
+    impl Y for () {
+        type T = u32;
+        type V = Vec<u8>;
+    }
+
+    // Can't constrain `X::T` through `Y`
+    fn f() -> impl X<T = i32> + Y {}
+    fn f2() -> impl X<T = i32> + Y<T = u32> {}
+
+    // X::T is never constrained in the first place, so it can be omitted
+    // and left unconstrained
+    fn f3() -> impl X + Y {}
+    fn f4() -> impl X + Y<T = u32> {}
+    fn f5() -> impl X<U = String> + Y<T = u32> {}
+}
+
 fn main() {}
diff --git a/tests/ui/implied_bounds_in_impls.stderr b/tests/ui/implied_bounds_in_impls.stderr
index fb44f2aba17..3b09e4582e3 100644
--- a/tests/ui/implied_bounds_in_impls.stderr
+++ b/tests/ui/implied_bounds_in_impls.stderr
@@ -192,5 +192,41 @@ LL -     fn f3() -> impl Trait3<i8, i16, i64, X = i32, Y = i128> + Trait4<i8, X
 LL +     fn f3() -> impl Trait4<i8, X = i32, Y = i128> {}
    |
 
-error: aborting due to 16 previous errors
+error: this bound is already specified as the supertrait of `Y`
+  --> $DIR/implied_bounds_in_impls.rs:148:21
+   |
+LL |     fn f3() -> impl X + Y {}
+   |                     ^
+   |
+help: try removing this bound
+   |
+LL -     fn f3() -> impl X + Y {}
+LL +     fn f3() -> impl Y {}
+   |
+
+error: this bound is already specified as the supertrait of `Y<T = u32>`
+  --> $DIR/implied_bounds_in_impls.rs:149:21
+   |
+LL |     fn f4() -> impl X + Y<T = u32> {}
+   |                     ^
+   |
+help: try removing this bound
+   |
+LL -     fn f4() -> impl X + Y<T = u32> {}
+LL +     fn f4() -> impl Y<T = u32> {}
+   |
+
+error: this bound is already specified as the supertrait of `Y<T = u32>`
+  --> $DIR/implied_bounds_in_impls.rs:150:21
+   |
+LL |     fn f5() -> impl X<U = String> + Y<T = u32> {}
+   |                     ^^^^^^^^^^^^^
+   |
+help: try removing this bound
+   |
+LL -     fn f5() -> impl X<U = String> + Y<T = u32> {}
+LL +     fn f5() -> impl Y<T = u32, U = String> {}
+   |
+
+error: aborting due to 19 previous errors