Fastlane Gym: Automating Builds With Extensions

Hey there, fellow iOS developers! Have you ever hit a snag when trying to automate your build process with Fastlane Gym, especially when your project has a bunch of extensions like Notification Service Extensions or Widget Extensions? You're not alone! It's a pretty common issue that can throw a wrench into your CI/CD pipeline. Let's dive into how to fix the target selection prompt that pops up when you're using gym and have multiple targets.

The Gym Dilemma: Target Selection Woes

So, you've got your main app, some test targets, and now you've added cool extensions to jazz things up. Great! But then you run fastlane gym, and bam! You're greeted with a prompt asking you to pick a target. This wasn't happening before you added those extensions, right? Here's what the prompt looks like:

[09:56:39]: What target would you like to use?
1. MainApp
2. MainAppTests
3. MainAppUITests
4. NotificationExtension
5. WidgetExtension

This is a real pain, especially when you're trying to automate your builds on a CI/CD server like Jenkins. You want gym to just know what to build based on your scheme, but it's not cooperating. Let's get into why this happens and how to fix it.

The Root of the Problem

The heart of the issue is that gym, by default, can get a bit confused when there are multiple targets in your Xcode project, even if your scheme is explicitly defined in your Fastfile. The scheme tells Xcode which target to build (along with its dependencies), but gym sometimes needs a little extra nudge to figure this out, especially when extensions are involved. Extensions add complexity, as they are built along with your main app target and can confuse Gym.

The Ideal Scenario and Why It's Not Happening

Ideally, gym should just use the scheme you've specified, build your app, and archive it without any interaction. This is exactly what we expect and what we want for seamless automation. You've probably got something like this in your Fastfile:

gym(
  configuration: "Release",
  scheme: "MainApp",
  export_method: "app-store",
  export_options: {
    provisioningProfiles: {
      "com.example.app" => "AppStoreProfile"
    }
  },
  include_bitcode: false,
  workspace: "MainApp.xcworkspace",
  output_directory: "./build",
  output_name: "MainApp"
)

Everything seems right, the scheme is there, the configuration is set, but still the prompt! This happens because gym isn't fully aware of your project structure, especially with extensions. Let's explore some solutions.

Strategies to Tame the Target Selection Beast

Let's go through some strategies to tell gym which target to build and avoid that pesky prompt. Remember, the goal is a fully automated build process.

1. Specifying build_path and xcargs (Not Always the Answer)

Some folks try adding xcargs to specify the target. You might have tried something like xcargs: "-destination generic/platform=iOS -target MainApp", or even xcargs: "-scheme MainApp". Unfortunately, this doesn't always work. Let's explore why and provide a more reliable solution.

The xcargs argument lets you pass extra arguments to xcodebuild, the underlying tool gym uses. Theoretically, you could use -target to specify the target. However, gym often ignores arguments passed through xcargs when the scheme is correctly defined. If you're lucky, it works, but it's not a surefire fix.

2. The clean Action (Sometimes Helps, but Not the Core Solution)

Before running gym, try adding clean to your Fastfile. This can help resolve build issues and make sure gym builds the proper target. Your Fastfile might look like:

  lane :build_app do
    clean
    gym(
      configuration: "Release",
      scheme: "MainApp",
      export_method: "app-store",
      export_options: {
        provisioningProfiles: {
          "com.example.app" => "AppStoreProfile"
        }
      },
      include_bitcode: false,
      workspace: "MainApp.xcworkspace",
      output_directory: "./build",
      output_name: "MainApp"
    )
  end

Cleaning the build folder forces Xcode to rebuild everything from scratch. This can help if previous builds or cruft are confusing the build process. However, this doesn't address the core issue and is often a shot in the dark.

3. The derived_data_path Trick (The Most Reliable Approach)

This is often the most reliable way to make gym select the correct target and avoid the prompt. By specifying the derived_data_path, you tell gym to use a specific location for its build artifacts. Because Xcode is managing the build process this way, it will use the scheme you provided in your fastfile and it won't ask for the target to build. Here's how to do it:

gym(
  configuration: "Release",
  scheme: "MainApp",
  export_method: "app-store",
  export_options: {
    provisioningProfiles: {
      "com.example.app" => "AppStoreProfile"
    }
  },
  include_bitcode: false,
  workspace: "MainApp.xcworkspace",
  output_directory: "./build",
  output_name: "MainApp",
  derived_data_path: "./DerivedData"
)

Make sure the directory you specify exists, and you're good to go. This typically tells gym to avoid the interactive prompt. The derived_data_path makes sure your builds are isolated, reducing the chance of conflicts and making the build process more predictable. This is often the magic bullet.

4. Verify Scheme Configuration

Ensure your scheme is properly configured. This might seem obvious, but it's a common source of problems. Open your Xcode project and go to Product > Scheme > Edit Scheme. Make sure:

• Build: All targets are included in the build phase. Specifically, your main app target and all the extensions. The build order here can influence things, so make sure your main app is first. Extensions should be built with your main app, not separately.
• Archive: The archive action uses the same configuration as the build action (typically 'Release' for distribution). The archive step is key for generating your .ipa file.
• Run: The run action uses the correct executable and configuration. This ensures that the app runs correctly during testing.

Sometimes, issues with scheme setup can lead to build errors or unexpected behavior during the archive process.

5. Check Xcode Version and Fastlane Version

Make sure your Xcode and Fastlane versions are compatible. Occasionally, there are bugs or incompatibilities between versions. Update to the latest stable versions of both tools to resolve any known issues.

Testing Your Changes

After making these changes, it's super important to test them out. Run fastlane gym locally to see if it works without prompting you for a target. If you're using a CI/CD system, trigger a build there to ensure the automation is working as expected.

Troubleshooting Tips

• Clean Build Folder: Before testing, clean your Xcode project. Go to Product > Clean Build Folder. This can clear out old build artifacts that might be causing issues.
• Verbose Logging: Add verbose: true to your gym call in your Fastfile. This gives you a ton more output to help you diagnose any errors.
• Read the Logs: Carefully review the output from gym to pinpoint any errors or warnings. Pay close attention to what xcodebuild is doing under the hood.
• Check Provisioning Profiles: Verify your provisioning profiles and code signing settings. Mismatched profiles can cause build failures.

Wrapping Up: Automating Your Builds Like a Pro

By following these steps, you should be able to get gym to work seamlessly with extensions and avoid the target selection prompt. Using derived_data_path is the most reliable method, but double-check your scheme configuration and version compatibility too. Now you can focus on building great apps and let Fastlane handle the build and archive process.

Good luck, and happy coding, guys! Let me know if you have any questions or if you find any other useful tricks!