Fix the performance of selector span expansion

Instead of calling `SourceFile.getText()`, which creates string copies
of a substantial subset of the text of the file every time, this
directly accesses the file's underlying code units without doing any
copies.

Closes #1913

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 * **Potentially breaking change:** Drop support for End-of-Life Node.js 12.
 
+* Fix remaining cases for the performance regression introduced in 1.59.0.
+
 ### Embedded Sass
 
 * The JS embedded host now loads files from the working directory when using the

lib/src/interpolation_map.dart

@@ -6,7 +6,6 @@ import 'dart:math' as math;
 
 import 'package:charcode/charcode.dart';
 import 'package:source_span/source_span.dart';
-import 'package:string_scanner/string_scanner.dart';
 
 import 'ast/sass.dart';
 import 'util/character.dart';
@@ -125,21 +124,21 @@ class InterpolationMap {
   /// comment before the expression, but since it's only used for error
   /// reporting that's probably fine.
   int _expandInterpolationSpanLeft(FileLocation start) {
-    var source = start.file.getText(0, start.offset);
+    var source = start.file.codeUnits;
     var i = start.offset - 1;
-    while (true) {
-      var prev = source.codeUnitAt(i--);
+    while (i >= 0) {
+      var prev = source[i--];
       if (prev == $lbrace) {
-        if (source.codeUnitAt(i) == $hash) break;
+        if (source[i] == $hash) break;
       } else if (prev == $slash) {
-        var second = source.codeUnitAt(i--);
+        var second = source[i--];
         if (second == $asterisk) {
           while (true) {
-            var char = source.codeUnitAt(i--);
+            var char = source[i--];
             if (char != $asterisk) continue;
 
             do {
-              char = source.codeUnitAt(i--);
+              char = source[i--];
             } while (char == $asterisk);
             if (char == $slash) break;
           }
@@ -153,28 +152,29 @@ class InterpolationMap {
   /// Given the end of a [FileSpan] covering an interpolated expression, returns
   /// the offset of the interpolation's closing `}`.
   int _expandInterpolationSpanRight(FileLocation end) {
-    var scanner = StringScanner(end.file.getText(end.offset));
-    while (true) {
-      var next = scanner.readChar();
+    var source = end.file.codeUnits;
+    var i = end.offset;
+    while (i < source.length) {
+      var next = source[i++];
       if (next == $rbrace) break;
       if (next == $slash) {
-        var second = scanner.readChar();
+        var second = source[i++];
         if (second == $slash) {
-          while (!isNewline(scanner.readChar())) {}
+          while (!isNewline(source[i++])) {}
         } else if (second == $asterisk) {
           while (true) {
-            var char = scanner.readChar();
+            var char = source[i++];
             if (char != $asterisk) continue;
 
             do {
-              char = scanner.readChar();
+              char = source[i++];
             } while (char == $asterisk);
             if (char == $slash) break;
           }
         }
       }
     }
 
-    return end.offset + scanner.position;
+    return i;
   }
 }

pkg/sass_api/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 6.2.0
+
+* No user-visible changes.
+
 ## 6.1.0
 
 * 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: 6.1.0
+version: 6.2.0
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 
 environment:
   sdk: ">=2.17.0 <3.0.0"
 
 dependencies:
-  sass: 1.60.0
+  sass: 1.61.0
 
 dev_dependencies:
   dartdoc: ^5.0.0

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.61.0-dev
+version: 1.61.0
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass
 
@@ -23,7 +23,7 @@ dependencies:
   path: ^1.8.0
   pub_semver: ^2.0.0
   source_maps: ^0.10.10
-  source_span: ^1.8.1
+  source_span: ^1.10.0
   stack_trace: ^1.10.0
   stream_transform: ^2.0.0
   string_scanner: ^1.1.0