Add regression tests for op_ref

tests/ui/eq_op.rs

@@ -2,7 +2,7 @@
 #![plugin(clippy)]
 
 #[deny(eq_op)]
-#[allow(identity_op, double_parens)]
+#[allow(identity_op, double_parens, many_single_char_names)]
 #[allow(no_effect, unused_variables, unnecessary_operation, short_circuit_statement)]
 #[deny(nonminimal_bool)]
 fn main() {
@@ -59,4 +59,40 @@ fn main() {
     a == a;
     2*a.len() == 2*a.len(); // ok, functions
     a.pop() == a.pop(); // ok, functions
+
+    use std::ops::BitAnd;
+    struct X(i32);
+    impl BitAnd for X {
+        type Output = X;
+        fn bitand(self, rhs: X) -> X {
+            X(self.0 & rhs.0)
+        }
+    }
+    impl<'a> BitAnd<&'a X> for X {
+        type Output = X;
+        fn bitand(self, rhs: &'a X) -> X {
+            X(self.0 & rhs.0)
+        }
+    }
+    let x = X(1);
+    let y = X(2);
+    let z = x & &y;
+
+    #[derive(Copy, Clone)]
+    struct Y(i32);
+    impl BitAnd for Y {
+        type Output = Y;
+        fn bitand(self, rhs: Y) -> Y {
+            Y(self.0 & rhs.0)
+        }
+    }
+    impl<'a> BitAnd<&'a Y> for Y {
+        type Output = Y;
+        fn bitand(self, rhs: &'a Y) -> Y {
+            Y(self.0 & rhs.0)
+        }
+    }
+    let x = Y(1);
+    let y = Y(2);
+    let z = x & &y;
 }

tests/ui/eq_op.stderr

@@ -219,5 +219,15 @@ error: equal expressions as operands to `==`
 59 |     a == a;
    |     ^^^^^^
 
+warning: taken reference of right operand
+  --> $DIR/eq_op.rs:97:13
+   |
+97 |     let z = x & &y;
+   |             ^^^^^^
+   |
+   = note: #[warn(op_ref)] on by default
+help: use the right value directly
+   |     let z = y & &y;
+
 error: aborting due to 32 previous errors