SwiftPM plugin doesn't work when integrated in the build phases of an Xcode project that contains nested SwiftPM packages

[nkristek]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

I have an Xcode project for an iOS app that contains nested SwiftPM packages. Until now SwiftLint was configured to run as a build phase that uses the installed version of the system, now I want to use the new SwiftPM plugin integration instead (to benefit from easier versioning control across multiple developers).

When using the SwiftLint plugin in the nested SwiftPM packages using the following code in the corresponding Package.swift:

dependencies: [
    .package(url: "https://github.com/realm/SwiftLint.git", branch: "main")
]
// ...
plugins: [
    .plugin(name: "SwiftLintPlugin", package: "SwiftLint")
]

the plugin works as intended.

However, when I try to integrate the plugin in the project (in order to lint the main app target) using the instructions here (adding the plugin in the Run Build Tool Plug-ins build phase), building the project fails with the error:

ld: entry point (_main) undefined. for architecture arm64

I'm building the project on an Apple Silicon based machine, but running Xcode under Rosetta2 results in the same error, but listing the Intel architecture instead. I've tried this in multiple codebases including a fresh iOS app (using the Xcode template) and I found out it always occurs once the project has a nested SwiftPM package.

Steps to reproduce

• Using Xcode 14.1
• Create a new project using the App template in the iOS category
  • Select Storyboard and Swift without Core Data or Tests
• Now we'll add the nested SwiftPM package
• Using Finder create a new folder called NestedModule inside the project folder
• In that folder create a new file called Package.swift with these contents:

// swift-tools-version:5.7

import PackageDescription

let package = Package(
    name: "NestedModule",
    platforms: [
        .iOS(.v14),
    ],
    products: [
        .library(name: "Nested", targets: ["Nested"])
    ],
    targets: [
        .target(name: "Nested")
    ]
)

• In the same folder create a new folder called Sources
• Inside Sources create a folder called Nested
• Inside Nested create an empty file called File.swift (to silence the warning about no source files)
• Drag the folder NestedModule into Xcode directly below the project
  • Instead of having a normal folder icon, the icon should be that of a SwiftPM package, if it doesn't, please restart Xcode
• In the project file > target > Frameworks, Libraries, and Embedded Content: press + to add the Nested module
• Try to build the project -> succeeds
• In the project file > project > SwiftPM dependencies: add SwiftLint (https://github.com/realm/SwiftLint.git targeting the main branch) without ticking any boxes when being asked if it should be included in the app
• In the project file > target > build phases tab > Run Build Tool Plug-ins: press + to add the SwiftLint plug-in
• Try to build the project -> fails with error ld: entry point (_main) undefined. for architecture arm64

Environment

• SwiftLint version (run swiftlint version to be sure)?

  • main branch (which currently uses a prebuilt binary of 0.50.1 under the hood)

• Installation method used (Homebrew, CocoaPods, building from source, etc)?

  • SwiftPM

• Paste your configuration file:

  • Default

• Are you using nested configurations?

  • No

• Which Xcode version are you using (check xcodebuild -version)?

  • 14.1

• Do you have a sample that shows the issue?

  • Reproducible with the steps above

[jpsim]

@technocidal some more plugin issues if you can take a look at this.

[technocidal]

@jpsim I'll take a look.

[technocidal]

@nkristek

I was able to reproduce your issue. Thanks for the perfect description.

Looking around for some indication as this is quite a generic error I found this thread which dealt with problems regarding the @main annotation. In that context it was the reason why the plugin didn't work, but for some reason this also works for this problem.

So I've added

@main
struct Nested {
    static func main() {}
}

to the empty package and Xcode stopped complaining and SwiftLint worked as expected.

I don't have any clue why this is the case. The @main syntax was introduced as a replacement for the main.swift convention and for some reason if a local package doesn't use it, Xcode falls down.

Could you try this with one of your actual packages and report back if it fixes it there as well?

[nkristek]

Thank you for your quick response! Amazingly this works!

Wow, this sounds like it is an issue in Xcode. Since the NestedModule package doesn't expose an executable product itself, I wouldn't have guessed that adding a main function there would fix the error.

I very much appreciate that you looked into it and I would consider this issue here solved.

[nkristek]

Unfortunately I just found out, that even though the iOS app builds now, it doesn't properly run anymore as soon as any nested package has a type annotated with @main. The compiler prefers this empty main function over my appdelegate, which is defined in the main app target and also annotated with @main.

I will still leave this issue closed (unless you think otherwise), since I believe this issue is not caused by SwiftLint and instead caused by a bug in Xcode.

[mccarron]

Seeing the same issue on our iOS target trying to move SwiftLint to an Xcode plugin on Xcode 14.1.

We don't have any custom Swift Packages nested, just other third party packages. So yeah this sounds like an Xcode issue maybe?

[technocidal]

@mccarron @nkristek

That sucks. Do we've enough information to open a Radar?

[mccarron]

Going to try a few things myself:

• Test on Xcode 14.2 GM that just came out yesterday
• Create a sample project that breaks with minimal inputs vs our current project

Hopefully Xcode 14.2 fixes it, if not I'll send Apple the sample project where this breaks. Will report back here.

[nkristek]

@technocidal @mccarron
I've tried the Xcode 14.2 RC and the result is unfortunately the same.

[jpsim]

Once someone's filed a feedback with Apple on this, I can try to get it looked at.

[technocidal]

@nkristek

I'm currently filing the feedback and adding the package inside the project directory consistently fails. I can only get it to show up if the NestedModule directory is outside the actual project directory. I'm pretty sure that's a separate issue, but I'll adapt your steps to reproduce as to not make the feedback even more confusing. The underlying issue is still reproducible.

[technocidal]

And just as I try to file the feedback they completely break new project creation with Xcode 14.2. I'll file this using Xcode 14.2 anyway as we're having issues building, but the project definitely doesn't run at all.

https://developer.apple.com/forums/thread/721912

[technocidal]

@jpsim @nkristek @mccarron

Posted feedback https://feedbackassistant.apple.com/feedback/11877146