feat: make avoid-unnecessary-type-assertions handle is! checks (#995)

* make avoid-unnecessary-type-assertions handle is! checks

* feat: make avoid-unnecessary-type-assertions handle is! checks

* test: update tests

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: incendial

CHANGELOG.md

@@ -4,7 +4,8 @@
 
 * feat: support passing file paths to all commands.
 * fix: avoid-top-level-members-in-tests ignore lib
-* fix: `--reporter=json` for `check-unnecessary-nullable` crashes, saying `Converting object to an encodable object failed: Instance of 'MappedIterable<FormalParameter, String>'`
+* fix: `--reporter=json` for `check-unnecessary-nullable` crashes, saying `Converting object to an encodable object failed: Instance of 'MappedIterable<FormalParameter, String>'`.
+* feat: make [`avoid-unnecessary-type-assertions`](https://dartcodemetrics.dev/docs/rules/common/avoid-unnecessary-type-assertions) handle is! checks.
 
 ## 4.18.0-dev.2
 

lib/src/analyzers/lint_analyzer/rules/rules_list/avoid_unnecessary_type_assertions/visitor.dart

@@ -42,13 +42,25 @@ class _Visitor extends RecursiveAstVisitor<void> {
 
     final objectType = node.expression.staticType;
     final castedType = node.type.type;
+
+    if (node.notOperator != null) {
+      if (_isUselessTypeCheck(castedType, objectType, true)) {
+        _expressions[node] =
+            '${node.isOperator.keyword?.lexeme ?? ''}${node.notOperator ?? ''}';
+      }
+    }
+
     if (_isUselessTypeCheck(objectType, castedType)) {
       _expressions[node] =
           '${node.isOperator.keyword?.lexeme ?? ''}${node.notOperator ?? ''}';
     }
   }
 
-  bool _isUselessTypeCheck(DartType? objectType, DartType? castedType) {
+  bool _isUselessTypeCheck(
+    DartType? objectType,
+    DartType? castedType, [
+    bool isReversed = false,
+  ]) {
     if (objectType == null || castedType == null) {
       return false;
     }
@@ -60,14 +72,14 @@ class _Visitor extends RecursiveAstVisitor<void> {
     final objectCastedType =
         _foundCastedTypeInObjectTypeHierarchy(objectType, castedType);
     if (objectCastedType == null) {
-      return false;
+      return isReversed;
     }
 
     if (!_checkGenerics(objectCastedType, castedType)) {
       return false;
     }
 
-    return true;
+    return !isReversed;
   }
 
   bool _checkNullableCompatibility(DartType objectType, DartType castedType) {

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_unnecessary_type_assertions/avoid_unnecessary_type_assertions_rule_test.dart

@@ -7,6 +7,7 @@ import '../../../../../helpers/rule_test_helper.dart';
 const _path = 'avoid_unnecessary_type_assertions/examples';
 const _classExampleWithIs = '$_path/example_with_is.dart';
 const _classExampleCases = '$_path/example_cases.dart';
+const _notIsExamplePath = '$_path/example_with_not_is.dart';
 
 void main() {
   group('AvoidUnnecessaryTypeAssertionsRule', () {
@@ -21,7 +22,7 @@ void main() {
       );
     });
 
-    test('reports about found all issues in example_with_is.dart', () async {
+    test('reports about all found issues in example_with_is.dart', () async {
       final unit = await RuleTestHelper.resolveFromFile(_classExampleWithIs);
       final issues = AvoidUnnecessaryTypeAssertionsRule().check(unit);
 
@@ -45,6 +46,7 @@ void main() {
           67,
           77,
           78,
+          80,
           81,
           82,
           86,
@@ -69,6 +71,7 @@ void main() {
           18,
           18,
           21,
+          21,
           18,
           21,
           18,
@@ -93,6 +96,7 @@ void main() {
           'nullableCats.whereType<Cat?>()',
           'cat is Cat?',
           'cat is! Cat?',
+          'cat is! Dog',
           'cat is Animal',
           'cat is! Animal',
           'dogs.whereType<Dog?>()',
@@ -117,6 +121,7 @@ void main() {
           'Avoid unnecessary "whereType<Cat?>()" assertion.',
           'Avoid unnecessary "is" assertion. The result is always "true".',
           'Avoid unnecessary "is!" assertion. The result is always "false".',
+          'Avoid unnecessary "is!" assertion. The result is always "false".',
           'Avoid unnecessary "is" assertion. The result is always "true".',
           'Avoid unnecessary "is!" assertion. The result is always "false".',
           'Avoid unnecessary "whereType<Dog?>()" assertion.',
@@ -126,7 +131,31 @@ void main() {
       );
     });
 
-    test('reports about found all issues in example_cases.dart', () async {
+    test(
+      'reports about all found issues in example_with_not_is.dart',
+      () async {
+        final unit = await RuleTestHelper.resolveFromFile(_notIsExamplePath);
+        final issues = AvoidUnnecessaryTypeAssertionsRule().check(unit);
+
+        RuleTestHelper.verifyIssues(
+          issues: issues,
+          startLines: [14, 16, 17],
+          startColumns: [17, 17, 17],
+          locationTexts: [
+            'cat is! Cat',
+            'cat is! Dog',
+            'cat is! NotAnimal',
+          ],
+          messages: [
+            'Avoid unnecessary "is!" assertion. The result is always "false".',
+            'Avoid unnecessary "is!" assertion. The result is always "false".',
+            'Avoid unnecessary "is!" assertion. The result is always "false".',
+          ],
+        );
+      },
+    );
+
+    test('reports about all found issues in example_cases.dart', () async {
       final unit = await RuleTestHelper.resolveFromFile(_classExampleCases);
       final issues = AvoidUnnecessaryTypeAssertionsRule().check(unit);
 

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_unnecessary_type_assertions/examples/example_with_is.dart

@@ -77,7 +77,7 @@ void checkSameOrInheritor() {
   final check1 = cat is Cat?; // Lint
   final check1Not = cat is! Cat?; // Lint
   final check2 = cat is Dog;
-  final check2Not = cat is! Dog;
+  final check2Not = cat is! Dog; // LINT
   final check3 = cat is Animal; // Lint
   final check3Not = cat is! Animal; // Lint
   final check4 = homeAnimal is Dog?;

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_unnecessary_type_assertions/examples/example_with_not_is.dart

@@ -0,0 +1,22 @@
+class Animal {}
+
+class NotAnimal {}
+
+class HomeAnimal extends Animal {}
+
+class Dog extends HomeAnimal {}
+
+class Cat extends HomeAnimal {}
+
+void checkSameOrInheritor() {
+  final cat = Cat();
+
+  final check = cat is! Cat; // Lint
+  final check = cat is Dog;
+  final check = cat is! Dog; // LINT
+  final check = cat is! NotAnimal; // Lint
+
+  final Cat? nullableCat = null;
+
+  final check = nullableCat is! Cat;
+}