Fix performance regression from selector spans (#1916)

Author: jathak

.github/workflows/ci.yml

@@ -140,6 +140,11 @@ jobs:
         dart_channel: [stable]
         node_version: [18]
         include:
+          # Temporarily adding back Node 12 here until we actually drop support
+          # in the package.json.
+          - os: ubuntu-latest
+            dart_channel: stable
+            node_version: 12
           # Include LTS versions on Ubuntu
           - os: ubuntu-latest
             dart_channel: stable
@@ -150,7 +155,6 @@ jobs:
           - os: ubuntu-latest
             dart_channel: dev
             node_version: 18
-
     steps:
       - uses: actions/checkout@v3
       - uses: dart-lang/setup-dart@v1

CHANGELOG.md

@@ -1,3 +1,13 @@
+## 1.59.3
+
+* Fix a performance regression introduced in 1.59.0.
+
+* The NPM release of 1.59.0 dropped support for Node 12 without actually
+  indicating so in its pubspec. This release temporarily adds back support so
+  that the latest Sass version that declares it supports Node 12 actually does
+  so. However, Node 12 is now end-of-life, so we will drop support for it
+  properly in an upcoming release.
+
 ## 1.59.2
 
 * No user-visible changes.

lib/src/parse/parser.dart

@@ -11,6 +11,7 @@ import '../exception.dart';
 import '../interpolation_map.dart';
 import '../logger.dart';
 import '../util/character.dart';
+import '../util/lazy_file_span.dart';
 import '../utils.dart';
 
 /// The abstract base class for all parsers.
@@ -675,7 +676,10 @@ class Parser {
   @protected
   FileSpan spanFrom(LineScannerState state) {
     var span = scanner.spanFrom(state);
-    return _interpolationMap?.mapSpan(span) ?? span;
+    if (_interpolationMap != null) {
+      return LazyFileSpan(() => _interpolationMap!.mapSpan(span));
+    }
+    return span;
   }
 
   /// Prints a warning to standard error, associated with [span].

lib/src/util/lazy_file_span.dart

@@ -0,0 +1,58 @@
+// Copyright 2023 Google LLC. 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';
+
+/// A wrapper for [FileSpan] that allows an expensive creation process to be
+/// deferred until the span is actually needed.
+class LazyFileSpan implements FileSpan {
+  /// The function that creates the underlying span.
+  final FileSpan Function() _builder;
+
+  /// The underlying span this wraps, which is created the first time this
+  /// getter is referenced.
+  FileSpan get span => _span ??= _builder();
+  FileSpan? _span;
+
+  /// Creates a new [LazyFileSpan] that defers calling [builder] until the
+  /// underlying span is needed.
+  LazyFileSpan(FileSpan Function() builder) : _builder = builder;
+
+  @override
+  int compareTo(SourceSpan other) => span.compareTo(other);
+
+  @override
+  String get context => span.context;
+
+  @override
+  FileLocation get end => span.end;
+
+  @override
+  FileSpan expand(FileSpan other) => span.expand(other);
+
+  @override
+  SourceFile get file => span.file;
+
+  @override
+  String highlight({color}) => span.highlight(color: color);
+
+  @override
+  int get length => span.length;
+
+  @override
+  String message(String message, {color}) =>
+      span.message(message, color: color);
+
+  @override
+  Uri? get sourceUrl => span.sourceUrl;
+
+  @override
+  FileLocation get start => span.start;
+
+  @override
+  String get text => span.text;
+
+  @override
+  SourceSpan union(SourceSpan other) => span.union(other);
+}

pkg/sass_api/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 6.0.3
+
+* No user-visible changes.
+
 ## 6.0.2
 
 * No user-visible changes.

pkg/sass_api/pubspec.yaml

@@ -2,15 +2,15 @@ name: sass_api
 # Note: Every time we add a new Sass AST node, we need to bump the *major*
 # version because it's a breaking change for anyone who's implementing the
 # visitor interface(s).
-version: 6.0.2
+version: 6.0.3
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 
 environment:
   sdk: ">=2.17.0 <3.0.0"
 
 dependencies:
-  sass: 1.59.2
+  sass: 1.59.3
 
 dev_dependencies:
   dartdoc: ^5.0.0

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.59.2
+version: 1.59.3
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass
 
@@ -35,7 +35,7 @@ dependencies:
 dev_dependencies:
   analyzer: ^4.7.0
   archive: ^3.1.2
-  cli_pkg: ^2.1.4
+  cli_pkg: ^2.4.2
   crypto: ^3.0.0
   dart_style: ^2.0.0
   dartdoc: ^6.0.0