New rule: no_condition_parens_rule (sass#15)

lib/src/engine.dart

@@ -9,6 +9,7 @@ import 'linter.dart';
 import 'rule.dart';
 import 'rules/no_debug.dart';
 import 'rules/no_empty_style.dart';
+import 'rules/no_condition_parens.dart';
 import 'rules/no_loud_comment.dart';
 import 'rules/non_numeric_dimension.dart';
 import 'rules/quote_map_keys.dart';
@@ -21,6 +22,7 @@ import 'rules/use_falsey_null.dart';
 final allRules = <Rule>[
   new NoDebugRule(),
   new NoEmptyStyleRule(),
+  new NoConditionParensRule(),
   new NoLoudCommentRule(),
   new NonNumericDimensionRule(),
   new QuoteMapKeysRule(),
@@ -86,7 +88,7 @@ class Engine {
 }
 
 Iterable<String> _scssFilesInDir(String path) => new Directory(path)
-      .listSync(recursive: true)
-      .where((entity) => entity is File)
-      .map((entity) => entity.path)
-      .where((path) => path.endsWith('.scss'));
+    .listSync(recursive: true)
+    .where((entity) => entity is File)
+    .map((entity) => entity.path)
+    .where((path) => path.endsWith('.scss'));

lib/src/rules/no_condition_parens.dart

@@ -0,0 +1,49 @@
+// Copyright 2018 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+// The sass package's API is not necessarily stable. It is being imported with
+// the Sass team's explicit knowledge and approval. See
+// https://github.com/sass/dart-sass/issues/236.
+import 'package:sass/src/ast/sass.dart';
+
+import '../lint.dart';
+import '../rule.dart';
+
+/// A lint rule that reports unnecessary parentheses in conditionals.
+///
+/// Sometimes users who are familiar with other languages forget that Sass
+/// doesn't need parentheses around its conditionals  (as in, `@if (...) {`, or
+/// `@else if (...) {`, or `@while (...) {`). This rule suggests removing these
+/// parentheses.
+class NoConditionParensRule extends Rule {
+  NoConditionParensRule() : super('no_condition_parens_rule');
+
+  @override
+  List<Lint> visitIfRule(IfRule node) {
+    var lint = <Lint>[];
+    for (var clause in node.clauses) {
+      if (clause.expression is ParenthesizedExpression) {
+        lint.add(Lint(
+            rule: this,
+            span: clause.expression.span,
+            message:
+                'Parentheses around ${clause.expression.span.text} are unnecessary'));
+      }
+    }
+    return lint..addAll(super.visitIfRule(node));
+  }
+
+  @override
+  List<Lint> visitWhileRule(WhileRule node) {
+    var lint = <Lint>[];
+    if (node.condition is ParenthesizedExpression) {
+      lint.add(Lint(
+          rule: this,
+          span: node.condition.span,
+          message:
+              'Parentheses around ${node.condition.span.text} are unnecessary'));
+    }
+    return lint..addAll(super.visitWhileRule(node));
+  }
+}

test/rules/no_condition_parens_test.dart

@@ -0,0 +1,67 @@
+// Copyright 2018 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:sass_linter/src/rules/no_condition_parens.dart';
+import 'package:sass_linter/src/lint.dart';
+import 'package:sass_linter/src/linter.dart';
+import 'package:test/test.dart';
+
+final url = 'a.scss';
+final rule = new NoConditionParensRule();
+
+void main() {
+  test('does not report lint when there are no parens', () {
+    var lints = getLints(r'@if 1 != 7 { @debug("quack"); }');
+
+    expect(lints, isEmpty);
+  });
+
+  test('reports lint when there is a paren in @if', () {
+    var lints = getLints(r'@if (1 != 7) { @debug("quack"); }');
+
+    expect(lints, hasLength(1));
+
+    var lint = lints.single;
+    expect(lint.rule, rule);
+    expect(lint.message, contains('Parentheses'));
+    expect(lint.message, contains('(1 != 7)'));
+    expect(lint.message, contains('unnecessary'));
+    expect(lint.url, new Uri.file(url));
+    expect(lint.line, 0);
+    expect(lint.column, 4);
+  });
+
+  test('reports lint when there is a paren in @else if', () {
+    var lints = getLints(r'@if 1 {} @else if (2 != 3) { @debug("quack"); }');
+
+    expect(lints, hasLength(1));
+
+    var lint = lints.single;
+    expect(lint.rule, rule);
+    expect(lint.message, contains('Parentheses'));
+    expect(lint.message, contains('(2 != 3)'));
+    expect(lint.message, contains('unnecessary'));
+    expect(lint.url, new Uri.file(url));
+    expect(lint.line, 0);
+    expect(lint.column, 18);
+  });
+
+  test('reports lint when there is a paren in @while', () {
+    var lints = getLints(r'@while (2 == 3) { @debug("quack"); }');
+
+    expect(lints, hasLength(1));
+
+    var lint = lints.single;
+    expect(lint.rule, rule);
+    expect(lint.message, contains('Parentheses'));
+    expect(lint.message, contains('(2 == 3)'));
+    expect(lint.message, contains('unnecessary'));
+    expect(lint.url, new Uri.file(url));
+    expect(lint.line, 0);
+    expect(lint.column, 18);
+  });
+}
+
+List<Lint> getLints(String source) =>
+    new Linter(source, [rule], url: url).run();