1 files changed, 49 insertions, 0 deletions
diff --git a/src/test/ui/impl-trait/equal-hidden-lifetimes.rs b/src/test/ui/impl-trait/equal-hidden-lifetimes.rs
new file mode 100644
index 000000000..79db88828
--- /dev/null
+++ b/src/test/ui/impl-trait/equal-hidden-lifetimes.rs
@@ -0,0 +1,49 @@
+// Test that we consider equal regions when checking for hidden regions in
+// opaque types
+
+// check-pass
+
+// `'a == 'static` so `&'a i32` is fine as the return type
+fn equal_regions_static<'a: 'static>(x: &'a i32) -> impl Sized {
+    //~^ WARNING unnecessary lifetime parameter `'a`
+    x
+}
+
+// `'a == 'b` so `&'b i32` is fine as the return type
+fn equal_regions<'a: 'b, 'b: 'a>(x: &'b i32) -> impl Sized + 'a {
+    let y: &'a i32 = x;
+    let z: &'b i32 = y;
+    x
+}
+
+// `'a == 'b` so `&'a i32` is fine as the return type
+fn equal_regions_rev<'a: 'b, 'b: 'a>(x: &'a i32) -> impl Sized + 'b {
+    let y: &'a i32 = x;
+    let z: &'b i32 = y;
+    x
+}
+
+// `'a == 'b` so `*mut &'b i32` is fine as the return type
+fn equal_regions_inv<'a: 'b, 'b: 'a>(x: *mut &'b i32) -> impl Sized + 'a {
+    let y: *mut &'a i32 = x;
+    let z: *mut &'b i32 = y;
+    x
+}
+
+// `'a == 'b` so `*mut &'a i32` is fine as the return type
+fn equal_regions_inv_rev<'a: 'b, 'b: 'a>(x: *mut &'a i32) -> impl Sized + 'b {
+    let y: *mut &'a i32 = x;
+    let z: *mut &'b i32 = y;
+    x
+}
+
+// Should be able to infer `fn(&'static ())` as the return type.
+fn contravariant_lub<'a, 'b: 'a, 'c: 'a, 'd: 'b + 'c>(
+    x: fn(&'b ()),
+    y: fn(&'c ()),
+    c: bool,
+) -> impl Sized + 'a {
+    if c { x } else { y }
+}
+
+fn main() {}