[ResidentFrontendServer] Fix Windows test failures

Fixes: #59659
Change-Id: I3ea0b01c1e12ada5e33b2a43106cd5e8f318eb28
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/399700
Reviewed-by: Ben Konyi <[email protected]>

Author: derekxu16

pkg/frontend_server/lib/resident_frontend_server_utils.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:convert' show jsonDecode;
-import 'dart:io' show Directory, File, InternetAddress, Platform, Socket;
+import 'dart:io' show Directory, File, InternetAddress, Socket;
 
 import 'package:path/path.dart' as path;
 
@@ -60,22 +60,15 @@ final class ResidentCompilerInfo {
 String computeCachedDillPath(
   final String canonicalizedLibraryPath,
 ) {
-  final int lastSeparatorPosInCanonicalizedLibraryPath =
-      canonicalizedLibraryPath.lastIndexOf(Platform.pathSeparator);
-  final String dirname = canonicalizedLibraryPath.substring(
-    0,
-    lastSeparatorPosInCanonicalizedLibraryPath,
-  );
-  final String basename = canonicalizedLibraryPath.substring(
-    lastSeparatorPosInCanonicalizedLibraryPath + 1,
-  );
+  final String dirname = path.dirname(canonicalizedLibraryPath);
+  final String basename = path.basename(canonicalizedLibraryPath);
 
   final String cachedKernelDirectoryPath = path.join(
     path.join(
       Directory.systemTemp.path,
       'dart_resident_compiler_kernel_cache',
     ),
-    dirname.replaceAll('/', '_').replaceAll(r'\', '_'),
+    dirname.replaceAll(new RegExp(r':|\\|\/'), '_'),
   );
 
   try {

pkg/frontend_server/test/src/resident_frontend_server_test.dart

@@ -8,7 +8,7 @@ import 'dart:io';
 
 import 'package:frontend_server/src/resident_frontend_server.dart';
 import 'package:frontend_server/resident_frontend_server_utils.dart'
-    show sendAndReceiveResponse;
+    show computeCachedDillPath, sendAndReceiveResponse;
 import 'package:frontend_server/starter.dart';
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
@@ -21,6 +21,40 @@ void main() async {
   // the unit tests will not be counted as modified.
   const int statGranularity = 1100;
 
+  group('Resident Frontend Server utility functions: ', () {
+    test('computeCachedDillPath', () async {
+      // [computeCachedDillPath] is implemented using [path.dirname] and
+      // [path.basename], and those functions are platform-sensitive, so we test
+      // with an example of a Windows path on Windows, and an example of a POSIX
+      // path on other platforms.
+      if (Platform.isWindows) {
+        const String exampleCanonicalizedLibraryPath =
+            r'C:\Users\user\directory\file.dart';
+        expect(
+          computeCachedDillPath(exampleCanonicalizedLibraryPath),
+          path.join(
+            Directory.systemTemp.path,
+            'dart_resident_compiler_kernel_cache',
+            'C__Users_user_directory_file',
+            'file.dart.dill',
+          ),
+        );
+      } else {
+        const String exampleCanonicalizedLibraryPath =
+            '/home/user/directory/file.dart';
+        expect(
+          computeCachedDillPath(exampleCanonicalizedLibraryPath),
+          path.join(
+            Directory.systemTemp.path,
+            'dart_resident_compiler_kernel_cache',
+            '_home_user_directory',
+            'file.dart.dill',
+          ),
+        );
+      }
+    });
+  });
+
   group('Resident Frontend Server: invalid input: ', () {
     test('no command given', () async {
       final String jsonResponse = await ResidentFrontendServer.handleRequest(