add invariance test

Author: b-naber

src/test/ui/mir/field-projection-invariant.rs

@@ -0,0 +1,24 @@
+// build-pass
+struct Inv<'a>(&'a mut &'a ());
+enum Foo<T> {
+    Bar,
+    Var(T),
+}
+type Supertype = Foo<for<'a> fn(Inv<'a>, Inv<'a>)>;
+
+fn foo(x: Foo<for<'a, 'b> fn(Inv<'a>, Inv<'b>)>) {
+    match x {
+        Supertype::Bar => {}
+        Supertype::Var(x) => {}
+    }
+}
+
+fn foo_nested(x: Foo<Foo<for<'a, 'b> fn(Inv<'a>, Inv<'b>)>>) {
+    match x {
+        Foo::Bar => {}
+        Foo::Var(Supertype::Bar) => {}
+        Foo::Var(Supertype::Var(x)) => {}
+    }
+}
+
+fn main() {}