null assert pattern support for null_check_on_nullable_type_parameter (#4148)

* null assert pattern support for `null_check_on_nullable_type_parameter`

* ++

* fmt

Author: pq

lib/src/rules/null_check_on_nullable_type_parameter.dart

@@ -70,6 +70,7 @@ class NullCheckOnNullableTypeParameter extends LintRule {
 
     var visitor = _Visitor(this, context);
     registry.addPostfixExpression(this, visitor);
+    registry.addRecordPattern(this, visitor);
   }
 }
 
@@ -79,19 +80,33 @@ class _Visitor extends SimpleAstVisitor<void> {
   final LinterContext context;
   _Visitor(this.rule, this.context);
 
+  bool isNullableTypeParameterType(DartType? type) =>
+      type is TypeParameterType && context.typeSystem.isNullable(type);
+
   @override
   void visitPostfixExpression(PostfixExpression node) {
     if (node.operator.type != TokenType.BANG) return;
 
     var expectedType = getExpectedType(node);
     var type = node.operand.staticType;
-    if (type is TypeParameterType &&
-        context.typeSystem.isNullable(type) &&
+    if (isNullableTypeParameterType(type) &&
         expectedType != null &&
         context.typeSystem.isPotentiallyNullable(expectedType) &&
-        context.typeSystem.promoteToNonNull(type) ==
+        context.typeSystem.promoteToNonNull(type!) ==
             context.typeSystem.promoteToNonNull(expectedType)) {
       rule.reportLintForToken(node.operator);
     }
   }
+
+  @override
+  void visitRecordPattern(RecordPattern node) {
+    for (var field in node.fields) {
+      var pattern = field.pattern;
+      if (pattern is NullAssertPattern) {
+        if (isNullableTypeParameterType(pattern.matchedValueType)) {
+          rule.reportLintForToken(pattern.operator);
+        }
+      }
+    }
+  }
 }

test/rule_test_support.dart

@@ -129,7 +129,7 @@ mixin LanguageVersion300Mixin on PubPackageResolutionTest {
 }
 
 abstract class LintRuleTest extends PubPackageResolutionTest {
-  bool get dumpAstOnFailures => false;
+  bool get dumpAstOnFailures => true;
 
   String? get lintRule;
 

test/rules/all.dart

@@ -58,6 +58,8 @@ import 'no_duplicate_case_values_test.dart' as no_duplicate_case_values;
 import 'non_adjacent_strings_in_list_test.dart' as no_adjacent_strings_in_list;
 import 'non_constant_identifier_names_test.dart'
     as non_constant_identifier_names;
+import 'null_check_on_nullable_type_parameter_test.dart'
+    as null_check_on_nullable_type_parameter;
 import 'null_closures_test.dart' as null_closures;
 import 'omit_local_variable_types_test.dart' as omit_local_variable_types;
 import 'one_member_abstracts_test.dart' as one_member_abstracts;
@@ -157,6 +159,7 @@ void main() {
   no_adjacent_strings_in_list.main();
   no_duplicate_case_values.main();
   non_constant_identifier_names.main();
+  null_check_on_nullable_type_parameter.main();
   null_closures.main();
   omit_local_variable_types.main();
   one_member_abstracts.main();

test/rules/null_check_on_nullable_type_parameter_test.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2023, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../rule_test_support.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(NullCheckOnNullableTypeParameterTestLanguage300);
+  });
+}
+
+@reflectiveTest
+class NullCheckOnNullableTypeParameterTestLanguage300 extends LintRuleTest
+    with LanguageVersion300Mixin {
+  @override
+  String get lintRule => 'null_check_on_nullable_type_parameter';
+
+  test_nullAssertPattern() async {
+    await assertDiagnostics(r'''
+void f<T>((T?, T?) p){
+  var (x!, y) = p;
+}
+''', [
+      error(HintCode.UNUSED_LOCAL_VARIABLE, 30, 1),
+      lint(31, 1),
+      error(HintCode.UNUSED_LOCAL_VARIABLE, 34, 1),
+    ]);
+  }
+}