fix(@angular-devkit/build-angular): use relative sourcemap source paths for Sass in esbuild builder

The Sass preprocessor's modern API will generate absolute file URLs for the `sources` field of generated
sourcemaps. These URLs will not be properly processed by esbuild and will not be correctly adjusted to be
relative to the workspace root directory for the built application. To correct this behavior, the Sass
generated sourcemaps are now adjusted to remove the `file:` protocol prefix and to make each path relative
to its input file. This allows esbuild to properly resolve and process the paths.

Author: clydin

packages/angular_devkit/build_angular/src/builders/browser-esbuild/sass-plugin.ts

@@ -7,8 +7,9 @@
  */
 
 import type { PartialMessage, Plugin, PluginBuild } from 'esbuild';
+import { dirname, relative } from 'node:path';
+import { fileURLToPath } from 'node:url';
 import type { CompileResult } from 'sass';
-import { fileURLToPath } from 'url';
 
 export function createSassPlugin(options: { sourcemap: boolean; loadPaths?: string[] }): Plugin {
   return {
@@ -40,7 +41,9 @@ export function createSassPlugin(options: { sourcemap: boolean; loadPaths?: stri
 
           return {
             loader: 'css',
-            contents: sourceMap ? `${css}\n${sourceMapToUrlComment(sourceMap)}` : css,
+            contents: sourceMap
+              ? `${css}\n${sourceMapToUrlComment(sourceMap, dirname(args.path))}`
+              : css,
             watchFiles: loadedUrls.map((url) => fileURLToPath(url)),
             warnings,
           };
@@ -66,7 +69,14 @@ export function createSassPlugin(options: { sourcemap: boolean; loadPaths?: stri
   };
 }
 
-function sourceMapToUrlComment(sourceMap: Exclude<CompileResult['sourceMap'], undefined>): string {
+function sourceMapToUrlComment(
+  sourceMap: Exclude<CompileResult['sourceMap'], undefined>,
+  root: string,
+): string {
+  // Remove `file` protocol from all sourcemap sources and adjust to be relative to the input file.
+  // This allows esbuild to correctly process the paths.
+  sourceMap.sources = sourceMap.sources.map((source) => relative(root, fileURLToPath(source)));
+
   const urlSourceMap = Buffer.from(JSON.stringify(sourceMap), 'utf-8').toString('base64');
 
   return `/*# sourceMappingURL=data:application/json;charset=utf-8;base64,${urlSourceMap} */`;