fix(compiler-cli): only read source-map comment from last line (#32912)

Source-maps can be linked to from a source-file by a comment at
the end of the file.

Previously the `SourceFileLoader` would read
the first comment that matched `//# sourceMappingURL=` but
this is not valid since some bundlers may include embedded
source-files that contain such a comment.

Now we only look for this comment in the last non-empty line
in the file.

PR Close #32912

Author: petebacondarwin

packages/compiler-cli/src/ngtsc/sourcemaps/src/source_file_loader.ts

@@ -102,12 +102,16 @@ export class SourceFileLoader {
    * whose path is indicated in a comment or implied from the name of the source file itself.
    */
   private loadSourceMap(sourcePath: AbsoluteFsPath, contents: string): MapAndPath|null {
-    const inline = commentRegex.exec(contents);
+    // Only consider a source-map comment from the last non-empty line of the file, in case there
+    // are embedded source-map comments elsewhere in the file (as can be the case with bundlers like
+    // webpack).
+    const lastLine = this.getLastNonEmptyLine(contents);
+    const inline = commentRegex.exec(lastLine);
     if (inline !== null) {
       return {map: fromComment(inline.pop()!).sourcemap, mapPath: null};
     }
 
-    const external = mapFileCommentRegex.exec(contents);
+    const external = mapFileCommentRegex.exec(lastLine);
     if (external) {
       try {
         const fileName = external[1] || external[2];
@@ -175,6 +179,20 @@ export class SourceFileLoader {
     this.currentPaths.push(path);
   }
 
+  private getLastNonEmptyLine(contents: string): string {
+    let trailingWhitespaceIndex = contents.length - 1;
+    while (trailingWhitespaceIndex > 0 &&
+           (contents[trailingWhitespaceIndex] === '\n' ||
+            contents[trailingWhitespaceIndex] === '\r')) {
+      trailingWhitespaceIndex--;
+    }
+    let lastRealLineIndex = contents.lastIndexOf('\n', trailingWhitespaceIndex - 1);
+    if (lastRealLineIndex === -1) {
+      lastRealLineIndex = 0;
+    }
+    return contents.substr(lastRealLineIndex + 1);
+  }
+
   /**
    * Replace any matched URL schemes with their corresponding path held in the schemeMap.
    *

packages/compiler-cli/src/ngtsc/sourcemaps/test/source_file_loader_spec.ts

@@ -63,6 +63,44 @@ runInEachFileSystem(() => {
         expect(sourceFile.rawMap).toEqual(sourceMap);
       });
 
+      it('should only read source-map comments from the last line of a file', () => {
+        fs.ensureDir(_('/foo/src'));
+        const sourceMap = createRawSourceMap({file: 'index.js'});
+        fs.writeFile(_('/foo/src/external.js.map'), JSON.stringify(sourceMap));
+        const sourceFile = registry.loadSourceFile(_('/foo/src/index.js'), [
+          'some content',
+          '//# sourceMappingURL=bad.js.map',
+          'some more content',
+          '//# sourceMappingURL=external.js.map',
+        ].join('\n'));
+        if (sourceFile === null) {
+          return fail('Expected source file to be defined');
+        }
+        expect(sourceFile.rawMap).toEqual(sourceMap);
+      });
+
+      for (const eolMarker of ['\n', '\r\n']) {
+        it(`should only read source-map comments from the last non-blank line of a file [EOL marker: ${
+               eolMarker === '\n' ? '\\n' : '\\r\\n'}]`,
+           () => {
+             fs.ensureDir(_('/foo/src'));
+             const sourceMap = createRawSourceMap({file: 'index.js'});
+             fs.writeFile(_('/foo/src/external.js.map'), JSON.stringify(sourceMap));
+             const sourceFile = registry.loadSourceFile(_('/foo/src/index.js'), [
+               'some content',
+               '//# sourceMappingURL=bad.js.map',
+               'some more content',
+               '//# sourceMappingURL=external.js.map',
+               '',
+               '',
+             ].join(eolMarker));
+             if (sourceFile === null) {
+               return fail('Expected source file to be defined');
+             }
+             expect(sourceFile.rawMap).toEqual(sourceMap);
+           });
+      }
+
       it('should handle a missing external source map', () => {
         fs.ensureDir(_('/foo/src'));
         const sourceFile = registry.loadSourceFile(