Handle CocoaPods ffi stderr (#102327)

Author: jmagman

packages/flutter_tools/lib/src/macos/cocoapods.dart

@@ -349,18 +349,19 @@ class CocoaPods {
   }
 
   void _diagnosePodInstallFailure(ProcessResult result) {
-    if (result.stdout is! String) {
+    final Object? stdout = result.stdout;
+    final Object? stderr = result.stderr;
+    if (stdout is! String || stderr is! String) {
       return;
     }
-    final String stdout = result.stdout as String;
     if (stdout.contains('out-of-date source repos')) {
       _logger.printError(
         "Error: CocoaPods's specs repository is too out-of-date to satisfy dependencies.\n"
         'To update the CocoaPods specs, run:\n'
         '  pod repo update\n',
         emphasis: true,
       );
-    } else if ((stdout.contains('ffi_c.bundle') || stdout.contains('/ffi/')) &&
+    } else if ((stderr.contains('ffi_c.bundle') || stderr.contains('/ffi/')) &&
         _operatingSystemUtils.hostPlatform == HostPlatform.darwin_arm) {
       // https://github.com/flutter/flutter/issues/70796
       UsageEvent(

packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart

@@ -514,7 +514,7 @@ Note: as of CocoaPods 1.0, `pod repo update` does not happen on `pod install` by
               'LANG': 'en_US.UTF-8',
             },
             exitCode: 1,
-            stdout: cocoaPodsError,
+            stderr: cocoaPodsError,
           ),
           const FakeCommand(
             command: <String>['which', 'sysctl'],