cmp_owned correct error message if rhs is deref

Author: JoshMcguigan

clippy_lints/src/misc.rs

@@ -579,6 +579,10 @@ fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr, other: &Expr) {
                     }
                 }
             }
+            if other_gets_derefed {
+                db.span_label(lint_span, "try implementing the comparison without allocating");
+                return;
+            }
             db.span_suggestion_with_applicability(
                 lint_span,
                 "try",

tests/ui/cmp_owned.stderr

@@ -40,13 +40,13 @@ error: this creates an owned instance just for comparison
   --> $DIR/cmp_owned.rs:42:5
    |
 42 |     y.to_owned() == *x;
-   |     ^^^^^^^^^^^^^^^^^^ help: try: `y == x`
+   |     ^^^^^^^^^^^^^^^^^^ try implementing the comparison without allocating
 
 error: this creates an owned instance just for comparison
   --> $DIR/cmp_owned.rs:47:5
    |
 47 |     y.to_owned() == **x;
-   |     ^^^^^^^^^^^^^^^^^^^ help: try: `y == *x`
+   |     ^^^^^^^^^^^^^^^^^^^ try implementing the comparison without allocating
 
 error: this creates an owned instance just for comparison
   --> $DIR/cmp_owned.rs:54:9