[ios] fix asset url not found when loading app extension (#46073)

In 9446392, I refactored the assetsPath to use NSURL. It turns out that when the app bundle is not loaded (during launching app exgtension), the assetURL will return nil using the `URLForResource`, but the `pathForResource` successfully returns the raw path.

This PR reverts back to the raw path solution.

part of flutter/flutter#124287

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: Chris Yang

shell/platform/darwin/common/framework/Source/FlutterNSBundleUtils.h

@@ -48,7 +48,7 @@ NSString* FLTAssetPath(NSBundle* bundle);
 // If the key is not set, `flutter_assets` is used as the raw path value.
 //
 // If no valid asset is found under the raw path, returns nil.
-NSURL* FLTAssetsURLFromBundle(NSBundle* bundle);
+NSString* FLTAssetsPathFromBundle(NSBundle* bundle);
 
 NS_ASSUME_NONNULL_END
 

shell/platform/darwin/common/framework/Source/FlutterNSBundleUtils.mm

@@ -54,15 +54,17 @@
 }
 
 NSString* FLTAssetPath(NSBundle* bundle) {
-  return [bundle objectForInfoDictionaryKey:@"FLTAssetsPath"] ?: kDefaultAssetPath;
+  return [bundle objectForInfoDictionaryKey:@"FLTAssetsPath"] ?: @"flutter_assets";
 }
 
-NSURL* FLTAssetsURLFromBundle(NSBundle* bundle) {
+NSString* FLTAssetsPathFromBundle(NSBundle* bundle) {
   NSString* flutterAssetsPath = FLTAssetPath(bundle);
-  NSURL* assets = [bundle URLForResource:flutterAssetsPath withExtension:nil];
+  // Use the raw path solution so that asset path can be returned from unloaded bundles.
+  // See https://github.com/flutter/engine/pull/46073
+  NSString* assetsPath = [bundle pathForResource:flutterAssetsPath ofType:@""];
 
-  if (!assets) {
-    assets = [[NSBundle mainBundle] URLForResource:flutterAssetsPath withExtension:nil];
+  if (assetsPath.length == 0) {
+    assetsPath = [[NSBundle mainBundle] pathForResource:flutterAssetsPath ofType:@""];
   }
-  return assets;
+  return assetsPath;
 }

shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm

@@ -139,19 +139,20 @@ static BOOL DoesHardwareSupportWideGamut() {
 
   // Checks to see if the flutter assets directory is already present.
   if (settings.assets_path.empty()) {
-    NSURL* assetsURL = FLTAssetsURLFromBundle(bundle);
+    NSString* assetsPath = FLTAssetsPathFromBundle(bundle);
 
-    if (!assetsURL) {
+    if (assetsPath.length == 0) {
       NSLog(@"Failed to find assets path for \"%@\"", bundle);
     } else {
-      settings.assets_path = assetsURL.path.UTF8String;
+      settings.assets_path = assetsPath.UTF8String;
 
       // Check if there is an application kernel snapshot in the assets directory we could
       // potentially use.  Looking for the snapshot makes sense only if we have a VM that can use
       // it.
       if (!flutter::DartVM::IsRunningPrecompiledCode()) {
         NSURL* applicationKernelSnapshotURL =
-            [assetsURL URLByAppendingPathComponent:@(kApplicationKernelSnapshotFileName)];
+            [NSURL URLWithString:@(kApplicationKernelSnapshotFileName)
+                   relativeToURL:[NSURL fileURLWithPath:assetsPath]];
         NSError* error;
         if ([applicationKernelSnapshotURL checkResourceIsReachableAndReturnError:&error]) {
           settings.application_kernel_asset = applicationKernelSnapshotURL.path.UTF8String;

shell/platform/darwin/ios/framework/Source/FlutterDartProjectTest.mm

@@ -89,31 +89,24 @@ - (void)testFLTGetApplicationBundleWhenCurrentTargetIsExtension {
 
 - (void)testFLTAssetsURLFromBundle {
   {
-    // Found asset path in info.plist (even not reachable)
+    // Found asset path in info.plist
     id mockBundle = OCMClassMock([NSBundle class]);
     OCMStub([mockBundle objectForInfoDictionaryKey:@"FLTAssetsPath"]).andReturn(@"foo/assets");
-    NSURL* mockAssetsURL = OCMClassMock([NSURL class]);
-    OCMStub([mockBundle URLForResource:@"foo/assets" withExtension:nil]).andReturn(mockAssetsURL);
-    OCMStub([mockAssetsURL checkResourceIsReachableAndReturnError:NULL]).andReturn(NO);
-    OCMStub([mockAssetsURL path]).andReturn(@"foo/assets");
-    NSURL* url = FLTAssetsURLFromBundle(mockBundle);
-    XCTAssertEqualObjects(url.path, @"foo/assets");
+    NSString* resultAssetsPath = @"path/to/foo/assets";
+    OCMStub([mockBundle pathForResource:@"foo/assets" ofType:@""]).andReturn(resultAssetsPath);
+    NSString* path = FLTAssetsPathFromBundle(mockBundle);
+    XCTAssertEqualObjects(path, @"path/to/foo/assets");
   }
   {
     // No asset path in info.plist, defaults to main bundle
     id mockBundle = OCMClassMock([NSBundle class]);
     id mockMainBundle = OCMPartialMock([NSBundle mainBundle]);
-    NSURL* mockAssetsURL = OCMClassMock([NSURL class]);
-    OCMStub([mockBundle URLForResource:@"Frameworks/App.framework/flutter_assets"
-                         withExtension:nil])
-        .andReturn(nil);
-    OCMStub([mockAssetsURL checkResourceIsReachableAndReturnError:NULL]).andReturn(NO);
-    OCMStub([mockAssetsURL path]).andReturn(@"path/to/foo/assets");
-    OCMStub([mockMainBundle URLForResource:@"Frameworks/App.framework/flutter_assets"
-                             withExtension:nil])
-        .andReturn(mockAssetsURL);
-    NSURL* url = FLTAssetsURLFromBundle(mockBundle);
-    XCTAssertEqualObjects(url.path, @"path/to/foo/assets");
+    NSString* resultAssetsPath = @"path/to/foo/assets";
+    OCMStub([mockBundle pathForResource:@"flutter_assets" ofType:@""]).andReturn(nil);
+    OCMStub([mockMainBundle pathForResource:@"flutter_assets" ofType:@""])
+        .andReturn(resultAssetsPath);
+    NSString* path = FLTAssetsPathFromBundle(mockBundle);
+    XCTAssertEqualObjects(path, @"path/to/foo/assets");
   }
 }