2 files changed, 33 insertions, 3 deletions
diff --git a/tests/ui/nonminimal_bool.rs b/tests/ui/nonminimal_bool.rs
index 1eecc3dee3d..cacce9a7d1c 100644
--- a/tests/ui/nonminimal_bool.rs
+++ b/tests/ui/nonminimal_bool.rs
@@ -236,3 +236,21 @@ mod issue14404 {
         }
     }
 }
+
+fn dont_simplify_double_not_if_types_differ() {
+    struct S;
+
+    impl std::ops::Not for S {
+        type Output = bool;
+        fn not(self) -> bool {
+            true
+        }
+    }
+
+    // The lint must propose `if !!S`, not `if S`.
+    // FIXME: `bool_comparison` will propose to use `S == true`
+    // which is invalid.
+    if !S != true {}
+    //~^ nonminimal_bool
+    //~| bool_comparison
+}
diff --git a/tests/ui/nonminimal_bool.stderr b/tests/ui/nonminimal_bool.stderr
index ecb82a23da0..c20412974b2 100644
--- a/tests/ui/nonminimal_bool.stderr
+++ b/tests/ui/nonminimal_bool.stderr
@@ -179,7 +179,7 @@ error: inequality checks against true can be replaced by a negation
   --> tests/ui/nonminimal_bool.rs:186:8
    |
 LL |     if !b != true {}
-   |        ^^^^^^^^^^ help: try simplifying it as shown: `!!b`
+   |        ^^^^^^^^^^ help: try simplifying it as shown: `b`
 
 error: this boolean expression can be simplified
   --> tests/ui/nonminimal_bool.rs:189:8
@@ -209,7 +209,7 @@ error: inequality checks against true can be replaced by a negation
   --> tests/ui/nonminimal_bool.rs:193:8
    |
 LL |     if true != !b {}
-   |        ^^^^^^^^^^ help: try simplifying it as shown: `!!b`
+   |        ^^^^^^^^^^ help: try simplifying it as shown: `b`
 
 error: this boolean expression can be simplified
   --> tests/ui/nonminimal_bool.rs:196:8
@@ -235,5 +235,17 @@ error: this boolean expression can be simplified
 LL |         if !(matches!(ty, TyKind::Ref(_, _, _)) && !is_mutable(&expr)) {
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `!matches!(ty, TyKind::Ref(_, _, _)) || is_mutable(&expr)`
 
-error: aborting due to 31 previous errors
+error: this boolean expression can be simplified
+  --> tests/ui/nonminimal_bool.rs:253:8
+   |
+LL |     if !S != true {}
+   |        ^^^^^^^^^^ help: try: `S == true`
+
+error: inequality checks against true can be replaced by a negation
+  --> tests/ui/nonminimal_bool.rs:253:8
+   |
+LL |     if !S != true {}
+   |        ^^^^^^^^^^ help: try simplifying it as shown: `!!S`
+
+error: aborting due to 33 previous errors