Add test for bad suggestion

src/test/ui/generic-associated-types/mismatched-where-clause-regions.rs

@@ -0,0 +1,12 @@
+trait Foo {
+    type T<'a1, 'b1>
+    where
+        'a1: 'b1;
+}
+
+impl Foo for () {
+    type T<'a2, 'b2> = () where 'b2: 'a2;
+    //~^ ERROR impl has stricter requirements than trait
+}
+
+fn main() {}

src/test/ui/generic-associated-types/mismatched-where-clause-regions.stderr

@@ -0,0 +1,17 @@
+error[E0276]: impl has stricter requirements than trait
+  --> $DIR/mismatched-where-clause-regions.rs:8:38
+   |
+LL |     type T<'a1, 'b1>
+   |     ---------------- definition of `T` from trait
+...
+LL |     type T<'a2, 'b2> = () where 'b2: 'a2;
+   |                                      ^^^ impl has extra requirement `'b2: 'a2`
+   |
+help: copy the `where` clause predicates from the trait
+   |
+LL |     type T<'a2, 'b2> = () where 'a2: 'b2;
+   |                           ~~~~~~~~~~~~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0276`.