Solve the problem that <Flutter/Flutter.h> cannot be imported when a pod transitive depends on Flutter (#125610)

![image](https://user-images.githubusercontent.com/8318578/234780282-89b18d27-df49-4b4e-88b5-c9d17cf3334f.png)
![image](https://user-images.githubusercontent.com/8318578/234780668-901ab816-5b6b-4d87-a6f4-120b5852580c.png)
If a pod transitive depends on a pod containing a framework, cocoapods will add the path of the framework to its FRAMEWORK_SEARCH_PATHS.
So I modified the relevant logic in podhelper, hoping to be consistent with the behavior of cocoapods.

Fixes https://github.com/flutter/flutter/issues/126251.

dev/devicelab/bin/tasks/plugin_test_ios.dart

@@ -9,6 +9,8 @@ Future<void> main() async {
   await task(combine(<TaskFunction>[
     PluginTest('ios', <String>['-i', 'objc', '--platforms=ios']).call,
     PluginTest('ios', <String>['-i', 'swift', '--platforms=ios']).call,
+    // Test that app builds with Flutter as a transitive dependency.
+    PluginTest('ios', <String>['-i', 'objc', '--platforms=ios'], cocoapodsTransitiveFlutterDependency: true).call,
     // Test that Dart-only plugins are supported.
     PluginTest('ios', <String>['--platforms=ios'], dartOnlyPlugin: true).call,
     // Test that shared darwin directories are supported.

dev/devicelab/lib/tasks/plugin_tests.dart

@@ -35,6 +35,7 @@ class PluginTest {
     this.dartOnlyPlugin = false,
     this.sharedDarwinSource = false,
     this.template = 'plugin',
+    this.cocoapodsTransitiveFlutterDependency = false,
   });
 
   final String buildTarget;
@@ -44,6 +45,7 @@ class PluginTest {
   final bool dartOnlyPlugin;
   final bool sharedDarwinSource;
   final String template;
+  final bool cocoapodsTransitiveFlutterDependency;
 
   Future<TaskResult> call() async {
     final Directory tempDir =
@@ -80,6 +82,11 @@ class PluginTest {
         await app.addPlugin('path_provider');
         section('Build app');
         await app.build(buildTarget, validateNativeBuildProject: !dartOnlyPlugin);
+        if (cocoapodsTransitiveFlutterDependency) {
+          section('Test app with Flutter as a transitive CocoaPods dependency');
+          await app.addCocoapodsTransitiveFlutterDependency();
+          await app.build(buildTarget, validateNativeBuildProject: !dartOnlyPlugin);
+        }
         if (runFlutterTest) {
           section('Test app');
           await app.runFlutterTest();
@@ -361,6 +368,57 @@ public class $pluginClass: NSObject, FlutterPlugin {
     return project;
   }
 
+  /// Creates a Pod that uses a Flutter plugin as a dependency and therefore
+  /// Flutter as a transitive dependency.
+  Future<void> addCocoapodsTransitiveFlutterDependency() async {
+    final String iosDirectoryPath = path.join(rootPath, 'ios');
+
+    final File nativePod = File(path.join(
+      iosDirectoryPath,
+      'NativePod',
+      'NativePod.podspec',
+    ));
+    nativePod.createSync(recursive: true);
+    nativePod.writeAsStringSync('''
+Pod::Spec.new do |s|
+  s.name             = 'NativePod'
+  s.version          = '1.0.0'
+  s.summary          = 'A pod to test Flutter as a transitive dependency.'
+  s.homepage         = 'https://flutter.dev'
+  s.license          = { :type => 'BSD' }
+  s.author           = { 'Flutter Dev Team' => 'flutter-dev@googlegroups.com' }
+  s.source           = { :path => '.' }
+  s.source_files = "Classes", "Classes/**/*.{h,m}"
+  s.dependency 'plugintest'
+end
+''');
+
+    final File nativePodClass = File(path.join(
+      iosDirectoryPath,
+      'NativePod',
+      'Classes',
+      'NativePodTest.m',
+    ));
+    nativePodClass.createSync(recursive: true);
+    nativePodClass.writeAsStringSync('''
+#import <Flutter/Flutter.h>
+
+@interface NativePodTest : NSObject
+
+@end
+
+@implementation NativePodTest
+
+@end
+''');
+
+    final File podfileFile = File(path.join(iosDirectoryPath, 'Podfile'));
+    final List<String> podfileContents = podfileFile.readAsLinesSync();
+    final int index = podfileContents.indexWhere((String line) => line.contains('flutter_install_all_ios_pods'));
+    podfileContents.insert(index, "pod 'NativePod', :path => 'NativePod'");
+    podfileFile.writeAsStringSync(podfileContents.join('\n'));
+  }
+
   // Make the platform version artificially low to test that the "deployment
   // version too low" warning is never emitted.
   void _reduceDarwinPluginMinimumVersion(String plugin, String target) {

packages/flutter_tools/bin/podhelper.rb

@@ -19,6 +19,20 @@ def flutter_ios_podfile_setup; end
 # Same as flutter_ios_podfile_setup for macOS.
 def flutter_macos_podfile_setup; end
 
+# Determine whether the target depends on Flutter (including transitive dependency)
+def depends_on_flutter(target, engine_pod_name)
+  target.dependencies.any? do |dependency|
+    if dependency.name == engine_pod_name
+      return true
+    end
+
+    if depends_on_flutter(dependency.target, engine_pod_name)
+      return true
+    end
+  end
+  return false
+end
+
 # Add iOS build settings to pod targets.
 #
 # @example
@@ -68,8 +82,8 @@ def flutter_additional_ios_build_settings(target)
     # ARC code targeting iOS 8 does not build on Xcode 14.3. Force to at least iOS 9.
     build_configuration.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '9.0' if force_to_arc_supported_min
 
-    # Skip other updates if it's not a Flutter plugin (transitive dependency).
-    next unless target.dependencies.any? { |dependency| dependency.name == 'Flutter' }
+    # Skip other updates if it does not depend on Flutter (including transitive dependency)
+    next unless depends_on_flutter(target, 'Flutter')
 
     # Bitcode is deprecated, Flutter.framework bitcode blob will have been stripped.
     build_configuration.build_settings['ENABLE_BITCODE'] = 'NO'
@@ -139,8 +153,8 @@ def flutter_additional_macos_build_settings(target)
     # ARC code targeting macOS 10.10 does not build on Xcode 14.3. Force to at least macOS 10.11.
     build_configuration.build_settings['MACOSX_DEPLOYMENT_TARGET'] = '10.11' if force_to_arc_supported_min
 
-    # Skip other updates if it's not a Flutter plugin (transitive dependency).
-    next unless target.dependencies.any? { |dependency| dependency.name == 'FlutterMacOS' }
+    # Skip other updates if it does not depend on Flutter (including transitive dependency)
+    next unless depends_on_flutter(target, 'FlutterMacOS')
 
     # Profile can't be derived from the CocoaPods build configuration. Use release framework (for linking only).
     configuration_engine_dir = local_engine || (build_configuration.type == :debug ? debug_framework_dir : release_framework_dir)