Fix string.insert with negative indices

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.48.1
+
+* Fix a bug in `string.insert` with certain negative indices.
+
 ## 1.48.0
 
 ### JS API
@@ -23,7 +27,7 @@
 
 * **Potentially breaking bug fix:** Match the specification of the new JS API by
   passing `undefined` rather than `null` to `Logger.warn()` for an unset `span`.
-  
+
 #### TypeScript Declarations
 
 * Add a declaration for the `LegacyPluginThis.options.context` field.

lib/src/functions/string.dart

@@ -66,7 +66,7 @@ final _insert = _function("insert", r"$string, $insert, $index", (arguments) {
   if (indexInt < 0) {
     // +1 because negative indexes start counting from -1 rather than 0, and
     // another +1 because we want to insert *after* that index.
-    indexInt = string.sassLength + indexInt + 2;
+    indexInt = math.max(string.sassLength + indexInt + 2, 0);
   }
 
   var codepointIndex = _codepointForIndex(indexInt, string.sassLength);

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.48.0
+version: 1.48.1-dev
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass