add use_if_null_to_convert_null_to_bool

example/all.yaml

@@ -171,6 +171,7 @@ linter:
     - unsafe_html
     - use_full_hex_values_for_flutter_colors
     - use_function_type_syntax_for_parameters
+    - use_if_null_to_convert_nulls_to_bools
     - use_is_even_rather_than_modulo
     - use_key_in_widget_constructors
     - use_late_for_private_fields_and_variables

lib/src/rules.dart

@@ -175,6 +175,7 @@ import 'rules/unrelated_type_equality_checks.dart';
 import 'rules/unsafe_html.dart';
 import 'rules/use_full_hex_values_for_flutter_colors.dart';
 import 'rules/use_function_type_syntax_for_parameters.dart';
+import 'rules/use_if_null_to_convert_nulls_to_bools.dart';
 import 'rules/use_is_even_rather_than_modulo.dart';
 import 'rules/use_key_in_widget_constructors.dart';
 import 'rules/use_late_for_private_fields_and_variables.dart';
@@ -364,6 +365,7 @@ void registerLintRules() {
     ..register(UnsafeHtml())
     ..register(UseFullHexValuesForFlutterColors())
     ..register(UseFunctionTypeSyntaxForParameters())
+    ..register(UseIfNullToConvertNullsToBools())
     ..register(UseIsEvenRatherThanModuloCheck())
     ..register(UseKeyInWidgetConstructors())
     ..register(UseLateForPrivateFieldsAndVariables())

lib/src/rules/use_if_null_to_convert_nulls_to_bools.dart

@@ -0,0 +1,84 @@
+// Copyright (c) 2021, 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:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/type.dart';
+
+import '../analyzer.dart';
+
+const _desc = r'Use if-null operators to convert nulls to bools.';
+
+const _details = r'''
+
+Use if-null operators to convert nulls to bools.
+
+**BAD:**
+```
+if (nullableBool == true) {
+}
+if (nullableBool != false) {
+}
+```
+
+**GOOD:**
+```
+if (nullableBool ?? false) {
+}
+if (nullableBool ?? true) {
+}
+```
+
+''';
+
+class UseIfNullToConvertNullsToBools extends LintRule implements NodeLintRule {
+  UseIfNullToConvertNullsToBools()
+      : super(
+          name: 'use_if_null_to_convert_nulls_to_bools',
+          description: _desc,
+          details: _details,
+          group: Group.style,
+        );
+
+  @override
+  void registerNodeProcessors(
+      NodeLintRegistry registry, LinterContext context) {
+    if (!context.isEnabled(Feature.non_nullable)) return;
+
+    final visitor = _Visitor(this, context);
+    registry.addBinaryExpression(this, visitor);
+  }
+}
+
+class _Visitor extends SimpleAstVisitor<void> {
+  final LintRule rule;
+  final LinterContext context;
+
+  _Visitor(this.rule, this.context);
+
+  @override
+  void visitBinaryExpression(BinaryExpression node) {
+    var type = node.leftOperand.staticType;
+    var right = node.rightOperand;
+    if (node.operator.type == TokenType.EQ_EQ &&
+        isNullableBool(type) &&
+        right is BooleanLiteral &&
+        right.value) {
+      rule.reportLint(node);
+    }
+    if (node.operator.type == TokenType.BANG_EQ &&
+        isNullableBool(type) &&
+        right is BooleanLiteral &&
+        !right.value) {
+      rule.reportLint(node);
+    }
+  }
+
+  bool isNullableBool(DartType? type) =>
+      type != null &&
+      type.isDartCoreBool &&
+      context.typeSystem.isNullable(type);
+}

test/rules/experiments/nnbd/rules/use_if_null_to_convert_nulls_to_bools.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2021, 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.
+
+// test w/ `pub run test -N use_if_null_to_convert_nulls_to_bools`
+
+m() {
+  bool? e;
+  bool r;
+  r = e == true; // LINT
+  r = e == false; // OK
+  r = e ?? false; // OK
+  r = e != false; // LINT
+  r = e != true; // OK
+  r = e ?? true; // OK
+}