1 files changed, 111 insertions, 0 deletions
diff --git a/src/test/ui/hr-subtype/hr-subtype.rs b/src/test/ui/hr-subtype/hr-subtype.rs
new file mode 100644
index 000000000..c770e0de8
--- /dev/null
+++ b/src/test/ui/hr-subtype/hr-subtype.rs
@@ -0,0 +1,111 @@
+// Targeted tests for the higher-ranked subtyping code.
+
+#![allow(dead_code)]
+
+// revisions: bound_a_vs_bound_a
+// revisions: bound_a_vs_bound_b
+// revisions: bound_inv_a_vs_bound_inv_b
+// revisions: bound_co_a_vs_bound_co_b
+// revisions: bound_a_vs_free_x
+// revisions: free_x_vs_free_x
+// revisions: free_x_vs_free_y
+// revisions: free_inv_x_vs_free_inv_y
+// revisions: bound_a_b_vs_bound_a
+// revisions: bound_co_a_b_vs_bound_co_a
+// revisions: bound_contra_a_contra_b_ret_co_a
+// revisions: bound_co_a_co_b_ret_contra_a
+// revisions: bound_inv_a_b_vs_bound_inv_a
+// revisions: bound_a_b_ret_a_vs_bound_a_ret_a
+
+//[bound_a_vs_bound_a] check-pass
+//[bound_a_vs_bound_b] check-pass
+//[bound_inv_a_vs_bound_inv_b] check-pass
+//[bound_co_a_vs_bound_co_b] check-pass
+//[free_x_vs_free_x] check-pass
+//[bound_co_a_b_vs_bound_co_a] check-pass
+//[bound_co_a_co_b_ret_contra_a] check-pass
+//[bound_a_b_vs_bound_a] check-pass
+//[bound_contra_a_contra_b_ret_co_a] check-pass
+
+fn gimme<T>(_: Option<T>) {}
+
+struct Inv<'a> {
+    x: *mut &'a u32,
+}
+
+struct Co<'a> {
+    x: fn(&'a u32),
+}
+
+struct Contra<'a> {
+    x: &'a u32,
+}
+
+macro_rules! check {
+    ($rev:ident: ($t1:ty, $t2:ty)) => {
+        #[cfg($rev)]
+        fn subtype<'x, 'y: 'x, 'z: 'y>() {
+            gimme::<$t2>(None::<$t1>);
+            //[free_inv_x_vs_free_inv_y]~^ ERROR
+        }
+
+        #[cfg($rev)]
+        fn supertype<'x, 'y: 'x, 'z: 'y>() {
+            gimme::<$t1>(None::<$t2>);
+            //[bound_a_vs_free_x]~^ ERROR
+            //[free_x_vs_free_y]~^^ ERROR
+            //[bound_inv_a_b_vs_bound_inv_a]~^^^ ERROR
+            //[bound_inv_a_b_vs_bound_inv_a]~| ERROR
+            //[bound_a_b_ret_a_vs_bound_a_ret_a]~^^^^^ ERROR
+            //[free_inv_x_vs_free_inv_y]~^^^^^^ ERROR
+        }
+    };
+}
+
+// If both have bound regions, they are equivalent, regardless of
+// variant.
+check! { bound_a_vs_bound_a: (for<'a> fn(&'a u32),
+for<'a> fn(&'a u32)) }
+check! { bound_a_vs_bound_b: (for<'a> fn(&'a u32),
+for<'b> fn(&'b u32)) }
+check! { bound_inv_a_vs_bound_inv_b: (for<'a> fn(Inv<'a>),
+for<'b> fn(Inv<'b>)) }
+check! { bound_co_a_vs_bound_co_b: (for<'a> fn(Co<'a>),
+for<'b> fn(Co<'b>)) }
+
+// Bound is a subtype of free.
+check! { bound_a_vs_free_x: (for<'a> fn(&'a u32),
+fn(&'x u32)) }
+
+// Two free regions are relatable if subtyping holds.
+check! { free_x_vs_free_x: (fn(&'x u32),
+fn(&'x u32)) }
+check! { free_x_vs_free_y: (fn(&'x u32),
+fn(&'y u32)) }
+check! { free_inv_x_vs_free_inv_y: (fn(Inv<'x>),
+fn(Inv<'y>)) }
+
+// Somewhat surprisingly, a fn taking two distinct bound lifetimes and
+// a fn taking one bound lifetime can be interchangeable, but only if
+// we are co- or contra-variant with respect to both lifetimes.
+//
+// The reason is:
+// - if we are covariant, then 'a and 'b can be set to the call-site
+//   intersection;
+// - if we are contravariant, then 'a can be inferred to 'static.
+check! { bound_a_b_vs_bound_a: (for<'a,'b> fn(&'a u32, &'b u32),
+for<'a>    fn(&'a u32, &'a u32)) }
+check! { bound_co_a_b_vs_bound_co_a: (for<'a,'b> fn(Co<'a>, Co<'b>),
+for<'a>    fn(Co<'a>, Co<'a>)) }
+check! { bound_contra_a_contra_b_ret_co_a: (for<'a,'b> fn(Contra<'a>, Contra<'b>) -> Co<'a>,
+for<'a>    fn(Contra<'a>, Contra<'a>) -> Co<'a>) }
+check! { bound_co_a_co_b_ret_contra_a: (for<'a,'b> fn(Co<'a>, Co<'b>) -> Contra<'a>,
+for<'a>    fn(Co<'a>, Co<'a>) -> Contra<'a>) }
+
+// If we make those lifetimes invariant, then the two types are not interchangeable.
+check! { bound_inv_a_b_vs_bound_inv_a: (for<'a,'b> fn(Inv<'a>, Inv<'b>),
+for<'a>    fn(Inv<'a>, Inv<'a>)) }
+check! { bound_a_b_ret_a_vs_bound_a_ret_a: (for<'a,'b> fn(&'a u32, &'b u32) -> &'a u32,
+for<'a>    fn(&'a u32, &'a u32) -> &'a u32) }
+
+fn main() {}