fix(@angular/build): watch all related files during a Sass error

When `dart-sass` returns an error, the provided location span may not be
the exact location of the error but can instead be the location of the
`@error` call within a Sass function. The generated stack trace string
does contain all files related to the error including the usage site in
the case of the function `@error` case. To ensure all related files for
the error are watched and allow for a rebuild that may correct the error,
the stack trace is parsed and found files are added to the watch list.
Unfortunately, `dart-sass` does not provide the list directly. If that
changes in the future, the stack trace parsing could be removed.

Author: clydin

packages/angular/build/src/tools/esbuild/stylesheets/sass-language.ts

@@ -174,6 +174,11 @@ async function compileString(
     if (isSassException(error)) {
       const fileWithError = error.span.url ? fileURLToPath(error.span.url) : undefined;
 
+      const watchFiles = [filePath, ...extractFilesFromStack(error.sassStack)];
+      if (fileWithError) {
+        watchFiles.push(fileWithError);
+      }
+
       return {
         loader: 'css',
         errors: [
@@ -182,7 +187,7 @@ async function compileString(
           },
         ],
         warnings,
-        watchFiles: fileWithError ? [filePath, fileWithError] : [filePath],
+        watchFiles,
       };
     }
 
@@ -202,3 +207,29 @@ function sourceMapToUrlComment(
 
   return `/*# sourceMappingURL=data:application/json;charset=utf-8;base64,${urlSourceMap} */`;
 }
+
+function* extractFilesFromStack(stack: string): Iterable<string> {
+  const lines = stack.split('\n');
+  const cwd = process.cwd();
+
+  // Stack line has format of "<file> <location> <identifier>"
+  for (const line of lines) {
+    const segments = line.split(' ');
+    if (segments.length < 3) {
+      break;
+    }
+
+    // Extract path from stack line.
+    // Paths may contain spaces. All segments before location are part of the file path.
+    let path = '';
+    let index = 0;
+    while (!segments[index].match(/\d+:\d+/)) {
+      path += segments[index++];
+    }
+
+    if (path) {
+      // Stack paths from dart-sass are relative to the current working directory (not input file or workspace root)
+      yield join(cwd, path);
+    }
+  }
+}