Flutter iOS build failure error with Multiple commands after the Xcode upgrade

If you have tried everything and still cannot build the Archive successfully, then you look like my case.

It took me 3 business days to fix this. My problem happened after adding the Notification Services target to the project. But it looks like it will apply to many other cases as well:

The problem is caused by the library inside 2 target multiple commands produce. In my case, for example, in the project target and notification extension target, both GoogleUtilities had this causing them to conflict or duplicated the commands produce. The solution is to make that dependency explicit, at the top level. The pod file will look like this:

platform :ios, '10.0'
use_frameworks!
inhibit_all_warnings!

pod 'GoogleUtilities' // Add this line is very important.

target 'MyProject' do
  pod 'Firebase/Analytics'
  pod 'Firebase/Crashlytics'
  pod 'Firebase/Messaging'
# Other pods
end

target 'NotificationService' do
  pod 'Firebase/Messaging'
end

After run:

pod deintegrate
pod install 

It's a known issue. Here is the explanation and some workarounds: https://github.com/flutter/flutter/issues/20685#issuecomment-421511890

Affected projects

This issue affects all Flutter projects built using Xcode 10 that have a dependency on CocoaPods -- typically this means those that rely on plugins. Workarounds

There are two workarounds:

• Option 1: Use the legacy build system . As noted by @gi097, open ios/Runner.xcworkspace, and change the build system to Legacy Build System.
• Option 2: Use the new Xcode 10 build system. Open ios/Runner.xcworkspace Select the Runner project in the project navigator sidebar. In the main view, select the Runner target, then select the Build Phases tab. Expand the Embed Frameworks phase and select Flutter.framework from the embedded frameworks list. Click - to remove Flutter.framework from the list (be sure to keep App.framework).

Root cause

When plugins are in use, there are two competing build actions that copy Flutter.framework into the build application Frameworks directory:

The Embed Frameworks build phase for the Runner project

The [CP] Embed Pods Frameworks build phase that pod install creates in the project.

Item (1) is there to ensure the framework is copied into the built app in the case where there are no plugins (and therefore no CocoaPods integration in the Xcode project). Item (2) is there because Flutter's podspec declares Flutter.framework as a vended_framework, and CocoaPods automatically adds a copy step for each such vended_framework in the transitive closure of CocoaPods dependencies.

This solution worked for me.

1. Open ios/Runner.xcworkspace Select the Runner project in the project navigator sidebar.
2. In the main view, select the Runner target, then select the Build Phases tab.
3. Expand the Embed Frameworks phase and select Flutter.framework from the embedded frameworks list.
4. Click - to remove Flutter.framework from the list (be sure to keep App.framework).