add tests

src/test/ui/mir/field-ty-ascription.rs

@@ -0,0 +1,21 @@
+// build-pass
+
+struct Foo<T>(T); // `T` is covariant.
+
+fn foo<'b>(x: Foo<for<'a> fn(&'a ())>) {
+    let Foo(y): Foo<fn(&'b ())> = x;
+}
+
+fn foo_nested<'b>(x: Foo<Foo<for<'a> fn(&'a ())>>) {
+    let Foo(Foo(y)): Foo<Foo<fn(&'b ())>> = x;
+}
+
+fn tuple<'b>(x: (u32, for<'a> fn(&'a ()))) {
+    let (_, y): (u32, fn(&'b ())) = x;
+}
+
+fn tuple_nested<'b>(x: (u32, (u32, for<'a> fn(&'a ())))) {
+    let (_, (_, y)): (u32, (u32, fn(&'b ()))) = x;
+}
+
+fn main() {}