Add a ParenthesizedExpression class (#503)

This allows us to accurately track the source spans for parenthesized
expressions, which in turn allows us to print accurate error
indications.

Adding a new class for this more accurately represents the structure
of the expression, but it also involves an extra allocation during
parsing and an extra level of nesting during evaluation which could
have a small but real performance impact.

We could alternatively add a package-internal setter for
Expression.span, and update the source span for parenthesized
expressions after they're initially parsed. However, this has its own
downsides: it adds complexity and mutability to the object model; and
many expression classes currently use lazily-generated spans, so
making them settable would require adding extra slots on those
classes.

I decided to go with the extra class because it only adds overhead
when parentheses are actually used in practice, as opposed to adding
overhead to every list/color/etc. The runtime overhead is also likely
to be mitigated if at any point we add a constant-folding step.

CHANGELOG.md

@@ -6,6 +6,9 @@
 * When running in compressed mode, remove spaces around combinators in complex
   selectors, so a selector like `a > b` is output as `a>b`.
 
+* Properly indicate the source span for errors involving binary operation
+  expressions whose operands are parenthesized.
+
 ## 1.14.2
 
 * Fix a bug where loading the same stylesheet from two different import paths

lib/src/ast/sass.dart

@@ -17,6 +17,7 @@ export 'sass/expression/list.dart';
 export 'sass/expression/map.dart';
 export 'sass/expression/null.dart';
 export 'sass/expression/number.dart';
+export 'sass/expression/parenthesized.dart';
 export 'sass/expression/selector.dart';
 export 'sass/expression/string.dart';
 export 'sass/expression/unary_operation.dart';

lib/src/ast/sass/expression/parenthesized.dart

@@ -0,0 +1,24 @@
+// 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:source_span/source_span.dart';
+
+import '../../../value.dart';
+import '../../../visitor/interface/expression.dart';
+import '../expression.dart';
+
+/// An expression wrapped in parentheses.
+class ParenthesizedExpression implements Expression {
+  /// The internal expression.
+  final Expression expression;
+
+  final FileSpan span;
+
+  ParenthesizedExpression(this.expression, this.span);
+
+  T accept<T>(ExpressionVisitor<T> visitor) =>
+      visitor.visitParenthesizedExpression(this);
+
+  String toString() => expression.toString();
+}

lib/src/parse/stylesheet.dart

@@ -1772,7 +1772,7 @@ relase. For details, see http://bit.ly/moz-document.
 
       if (!scanner.scanChar($comma)) {
         scanner.expectChar($rparen);
-        return first;
+        return new ParenthesizedExpression(first, scanner.spanFrom(start));
       }
       whitespace();
 

lib/src/visitor/async_evaluate.dart

@@ -1252,6 +1252,9 @@ class _EvaluateVisitor
   Future<SassNumber> visitNumberExpression(NumberExpression node) async =>
       new SassNumber(node.value, node.unit);
 
+  Future<Value> visitParenthesizedExpression(ParenthesizedExpression node) =>
+      node.expression.accept(this);
+
   Future<SassColor> visitColorExpression(ColorExpression node) async =>
       node.value;
 

lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/synchronize.dart for details.
 //
-// Checksum: f20e0967bae462f7d1728053fa0a41c09bcc0e03
+// Checksum: ce258987d3496f06c82ca1f31df4a0ac778fe326
 
 import 'async_evaluate.dart' show EvaluateResult;
 export 'async_evaluate.dart' show EvaluateResult;
@@ -1242,6 +1242,9 @@ class _EvaluateVisitor
   SassNumber visitNumberExpression(NumberExpression node) =>
       new SassNumber(node.value, node.unit);
 
+  Value visitParenthesizedExpression(ParenthesizedExpression node) =>
+      node.expression.accept(this);
+
   SassColor visitColorExpression(ColorExpression node) => node.value;
 
   SassList visitListExpression(ListExpression node) => new SassList(

lib/src/visitor/interface/expression.dart

@@ -17,6 +17,7 @@ abstract class ExpressionVisitor<T> {
   T visitMapExpression(MapExpression node);
   T visitNullExpression(NullExpression node);
   T visitNumberExpression(NumberExpression node);
+  T visitParenthesizedExpression(ParenthesizedExpression node);
   T visitSelectorExpression(SelectorExpression node);
   T visitStringExpression(StringExpression node);
   T visitUnaryOperationExpression(UnaryOperationExpression node);

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.14.3-dev
+version: 1.14.3
 description: A Sass implementation in Dart.
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/sass/dart-sass

test/cli/shared.dart

@@ -253,6 +253,24 @@ void sharedTests(Future<TestProcess> runSass(Iterable<String> arguments)) {
     await sass.shouldExit(65);
   });
 
+  // Regression test for an issue mentioned in sass/linter#15
+  test(
+      "gracefully reports errors for binary operations with parentheized "
+      "operands", () async {
+    var sass = await runSass(["-"]);
+    sass.stdin.writeln("a {b: (#123) + (#456)}");
+    sass.stdin.close();
+    expect(
+        sass.stderr,
+        emitsInOrder([
+          'Error: Undefined operation "#123 + #456".',
+          "a {b: (#123) + (#456)}",
+          "      ^^^^^^^^^^^^^^^",
+          "  - 1:7  root stylesheet",
+        ]));
+    await sass.shouldExit(65);
+  });
+
   test("gracefully handles a non-partial next to a partial", () async {
     await d.file("test.scss", "a {b: c}").create();
     await d.file("_test.scss", "x {y: z}").create();