[Lint] Prefer intValue.isEven check (#2076)
diff --git a/example/all.yaml b/example/all.yaml
index 8598d91..92a35c6 100644
--- a/example/all.yaml
+++ b/example/all.yaml
@@ -160,6 +160,7 @@
- unsafe_html
- use_full_hex_values_for_flutter_colors
- use_function_type_syntax_for_parameters
+ - use_is_even_rather_than_modulo
- use_key_in_widget_constructors
- use_raw_strings
- use_rethrow_when_possible
diff --git a/lib/src/rules.dart b/lib/src/rules.dart
index 5bc3f38..502e537 100644
--- a/lib/src/rules.dart
+++ b/lib/src/rules.dart
@@ -115,6 +115,7 @@
import 'rules/prefer_initializing_formals.dart';
import 'rules/prefer_inlined_adds.dart';
import 'rules/prefer_int_literals.dart';
+import 'rules/use_is_even_rather_than_modulo.dart';
import 'rules/prefer_interpolation_to_compose_strings.dart';
import 'rules/prefer_is_empty.dart';
import 'rules/prefer_is_not_empty.dart';
@@ -337,6 +338,7 @@
..register(UnsafeHtml())
..register(UseFullHexValuesForFlutterColors())
..register(UseFunctionTypeSyntaxForParameters())
+ ..register(UseIsEvenRatherThanModuloCheck())
..register(UseKeyInWidgetConstructors())
..register(UseRethrowWhenPossible())
..register(UseRawStrings())
diff --git a/lib/src/rules/use_is_even_rather_than_modulo.dart b/lib/src/rules/use_is_even_rather_than_modulo.dart
new file mode 100644
index 0000000..cfbb248
--- /dev/null
+++ b/lib/src/rules/use_is_even_rather_than_modulo.dart
@@ -0,0 +1,80 @@
+// Copyright (c) 2020, 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/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+import '../analyzer.dart';
+
+const _desc =
+ r'Prefer intValue.isOdd/isEven instead of checking the result of % 2.';
+
+const _details = r'''
+
+**PREFER** the use of intValue.isOdd/isEven to check for evenness.
+
+**BAD:**
+```
+bool isEven = 1 % 2 == 0;
+bool isOdd = 13 % 2 == 1;
+```
+
+**GOOD:**
+```
+bool isEven = 1.isEven;
+bool isOdd = 13.isOdd;
+```
+
+''';
+
+class UseIsEvenRatherThanModuloCheck extends LintRule implements NodeLintRule {
+ UseIsEvenRatherThanModuloCheck()
+ : super(
+ name: 'use_is_even_rather_than_modulo',
+ description: _desc,
+ details: _details,
+ group: Group.style);
+
+ @override
+ void registerNodeProcessors(NodeLintRegistry registry,
+ [LinterContext context]) {
+ final visitor = _Visitor(this);
+ registry.addBinaryExpression(this, visitor);
+ }
+}
+
+class _Visitor extends SimpleAstVisitor<void> {
+ final LintRule rule;
+ _Visitor(this.rule);
+
+ @override
+ void visitBinaryExpression(BinaryExpression node) {
+ // This lint error only happens when the operator is equality.
+ if (node.operator.type != TokenType.EQ_EQ) {
+ return;
+ }
+ var left = node.leftOperand;
+ var leftType = left.staticType;
+ var right = node.rightOperand;
+ var rightType = right.staticType;
+ // Both sides have to have static type of int
+ if (!(right is IntegerLiteral &&
+ leftType.isDartCoreInt == true &&
+ rightType.isDartCoreInt == true)) {
+ return;
+ }
+ // The left side expression has to be modulo by 2 type.
+ if (left is BinaryExpression) {
+ var rightChild = left.rightOperand;
+ var rightChildType = rightChild.staticType;
+ if (left.operator.type == TokenType.PERCENT &&
+ rightChild is IntegerLiteral &&
+ rightChild.value == 2 &&
+ rightChildType.isDartCoreInt == true) {
+ rule.reportLint(node);
+ }
+ }
+ }
+}
diff --git a/test/rules/use_is_even_rather_than_modulo.dart b/test/rules/use_is_even_rather_than_modulo.dart
new file mode 100644
index 0000000..d8d8ac7
--- /dev/null
+++ b/test/rules/use_is_even_rather_than_modulo.dart
@@ -0,0 +1,29 @@
+// Copyright (c) 2020, 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_is_even_rather_than_modulo`
+
+bool isEven = 1 % 2 == 0; //LINT
+bool isOdd = 13 % 2 == 1; //LINT
+int number = 3;
+bool c = number % 2 == 0; //LINT
+
+// Not equality operator is okay
+bool a = 1 % 2 >= 0;
+bool d = number % 2 != 0;
+
+// Modulo by any other number than 2 is okay
+d = number % 3 == 1;
+
+// Not modulo operation is okay.
+d = number + 2 == 0;
+
+// Compare to not an IntegerLiteral is okay.
+bool b = 1 % 2 == 3-3;
+// Unknown operand type is okay.
+Class tmp;
+a = tmp % 2 == 0;
+
+a = 1.isEven;
+a = 2.isOdd;
