Rollup merge of rust-lang#58725 - jamwt:fix-27949, r=Centril

Test that binop subtyping in rustc_typeck fixes rust-lang#27949

src/test/run-pass/issues/issue-27949.rs

@@ -0,0 +1,41 @@
+// run-pass
+//
+// At one time, the `==` operator (and other binary operators) did not
+// support subtyping during type checking, and would therefore require
+// LHS and RHS to be exactly identical--i.e. to have the same lifetimes.
+//
+// This was fixed in 1a7fb7dc78439a704f024609ce3dc0beb1386552.
+
+#[derive(Copy, Clone)]
+struct Input<'a> {
+    foo: &'a u32
+}
+
+impl <'a> std::cmp::PartialEq<Input<'a>> for Input<'a> {
+    fn eq(&self, other: &Input<'a>) -> bool {
+        self.foo == other.foo
+    }
+
+    fn ne(&self, other: &Input<'a>) -> bool {
+        self.foo != other.foo
+    }
+}
+
+
+fn check_equal<'a, 'b>(x: Input<'a>, y: Input<'b>) -> bool {
+    // Type checking error due to 'a != 'b prior to 1a7fb7dc78
+    x == y
+}
+
+fn main() {
+    let i = 1u32;
+    let j = 1u32;
+    let k = 2u32;
+
+    let input_i = Input { foo: &i };
+    let input_j = Input { foo: &j };
+    let input_k = Input { foo: &k };
+    assert!(check_equal(input_i, input_i));
+    assert!(check_equal(input_i, input_j));
+    assert!(!check_equal(input_i, input_k));
+}