Add support for Swift Package Manager (SPM) as the dependency manager for iOS

[sja26]

Introduction

Deprecate Cocoapods as the dependency manager for iOS, and add support for Swift Package Manager (SPM) as its successor.

Details

There is growing evidence that SPM is on a trajectory to replace Cocoapods as the most popular dependency manager for iOS apps.

I surmise that Cocoapods, being the only option to integrate React Native into an iOS app, is preventing a significant and growing number of iOS developers from trying out React Native.

Some background:

• Cocoapods was released in 2011 written in Ruby, it became the de facto dependency manager for iOS apps.
• SPM was released as part of Swift 3.0 in 2016.

References:

• Cocoapods
• Swift 3.0 Release
• SPM
• SPM on GitHub
• Migrating from CocoaPods to Swift Package Manager - Bitrise Blog
• Existing proposal?

Discussion points

Focusing on the data gathered by JetBrains' most recent annual survey for Swift and Objective-C developers in 2022. The results of 3 questions stand out as the main motivators to address the aforementioned trajectory of SPM.

Do you use Swift and Objective-C together in the same project?

• 62% Yes, most of my codebase is in Swift
• 23% Yes, most of my codebase is in Objective-C
• 16% No

Which dependency manager do you use?

• 61% CocoaPods
• 47% Swift Package Manager
• 18% None
• 11% Carthage
• 1% Other

Do you plan to replace CocoaPods dependencies with SPM packages?

• 48% No, and I don’t plan to in the next 12 months
• 28% Yes
• 24% No, but I plan to in the next 12 months

[nplasterer]

Just wanted to add some support for this discussion. We've been running into a lot of issues with trying to create a react native bridge to iOS for a react native SDK. The main issue is that our iOS SDK cannot be made into a cocoapod as one of our dependencies has dropped cocoapod support entirely https://forums.swift.org/t/swiftnio-is-dropping-support-for-cocoapods/56840. This has made it impossible for us to offer our integrators a RN SDK.

[cipolleschi]

Hi @sja26 and @nplasterer. Thank you for starting this proposal, it is very valuable indeed.

Swift Package Manager is something we are looking into as well, but currently it is not a feasible path for us.

The major blocker for this effort is that SPM, right now, does not support packages with mixed languages. A package in SPM must be only in Swift, Objective-C or C++. Whenever you try to mix them, SPM raises an error.

Other blockers:

• we are using Cocoapods also to run some scripts that prepares the project properly (setting the right flags) and that run Codegen.
  • Mitigation: both problems could be mitigated with the new Swift Plugins, but they are still in an unstable state (e.g.: it is not easy to integrate them with an App, see here, for example).
• the current structure of React Native does not work well with the structure suggested by SPM.
  • Mitigation: refactoring React Native and using the various SPM property in more advanced ways.

I would love to support you if you want to make some experiment with SPM to see how far you can go. I tried a couple of times in the past with not a lot of success, but I'm periodically try this path again because, as you, I also think that we should move to SPM at some point in the future.

[sja26]

Hi @cipolleschi, thank you for the summary.

Regarding the major blocker:

A package in SPM must be only in Swift, Objective-C or C++. Whenever you try to mix them, SPM raises an error.

Yes, but only if you want the package to include the source code. If not including the source code is acceptable then a binary framework can be distributed as a Swift package, which can be accomplished in two phases:

1. Creating an XCFramework
   Creating a multiplatform binary framework bundle (Apple Developer Article)
   Binary Frameworks in Swift (WWDC19)
2. Distributing as a Swift Package
   Distribute binary frameworks as Swift packages (Apple Developer Article)
   Distribute binary frameworks as Swift packages (WWDC20)

There are trade-offs when using binary frameworks as explained in the above resources, therefore this could be seen as an interim solution until SPM evolves to meet your original desire to include the source code in the Swift package.

we are using Cocoapods also to run some scripts that prepares the project properly (setting the right flags) and that run Codegen.

I wonder if using Gradle could be a suitable replacement see Building Swift projects?

the current structure of React Native does not work well with the structure suggested by SPM.

Could you elaborate further with an example please?

Fingers crossed WWDC23 will deliver more SPM improvements.

[cipolleschi]

If not including the source code is acceptable then a binary framework can be distributed as a Swift package.

@sja26 currently, React Native can't be really built as an isolated framework. 😅 The technical detail here is that the App is responsible to generate the code of Codegen, so that code won't be available in advance so that we can prepare a framework with it.
So the idea of shipping it as an XCFramework is not feasible as well. 😞

Also, I feel that being able to step into the React Native code is extremely useful for contributors that have to debug their libraries. We would like to keep this option open in the foreseeable future.

I wonder if using Gradle could be a suitable replacement see Building Swift projects?

Second problem, React Native internals can not be implemented in Swift. The core engine of React Native is in C++ and there is not full interoperability between Swift and C++. We should pass through Objective-C++, but the extra layer could have some performance implication (that we still have to test, thought) but that, so far, we haven't had time to explore. So, currently, we can't use Gradle to build Swift projects. However, it looks interesting and it could be interesting to use the same tooling for both Android and iOS.

Could you elaborate further with an example please?

React Native is structured as it follows (simplifying it):

• React (with iOS code)
• ReactCommon (with C++ code)

Within those folders, there are subfolders which are separated modules.
In some of those subfolders, there are folders called platform that contains ios, android and cxx folders for the specific platforms.

A simple difference between the structure suggested by SPM and our current structure is the absence of the Sources and Tests folders, for example. Also, we have nested folders that should be extracted in their own packages.

I'm not saying that it is not doable, but currently, this work will require a lot of effort and it will break several things also internally at Meta.

[chuckluck44]

@cipolleschi For clarification Swift Packages do support mixed languages without use of frameworks. The only requirement is that Swift and any C family languages be separated into their own folders/targets, but they ship as one product and the code can be stepped through normally.

Our own SDK is shipped as a swift package that uses a mix of swift, C, and C++. Swift is able to call C++ by wrapping calls in a C header in the c++ target, but Swift/C++ interoperability is also in the works https://github.com/apple/swift/tree/main/docs/CppInteroperability . You also have the option of creating a package completely in obj-c, c, and/or c++ (c++ requires a c or objc wrapper at the moment). In that case everything could be contained in a single target.

Regarding the folder structure issues, symlinks may work as a temporary fix. This is the approach we took when initially moving from an xcframework to swift package distribution. But that hasn't been tested in a while.

I understand this is a pretty large undertaking. There just isn't much of reason for newer iOS sdks to support CocoaPods st this point since SPM ships with xcode, can work in conjunction with both Carthage and CocoaPods (assuming there aren't any duplicated dependencies requirements across the graphs), and is much more tightly integrated with the ecosystem. Our SDK is only going to support cocoa pods because we have many integrators in our space that use react native and we need to distribute a node module, but other teams may just forgo supporting at all.

[cipolleschi]

@chuckluck44 I understand what you are saying. I completely agree that it is something important, but currently, we don't have much capacity to work on this, unfortunately.

The only requirement is that Swift and any C family languages be separated into their own folders/targets,

That's not the case, currently. For example, see the ImageManager. As you can see, in this folder we have a mixture of cpp and mm files. Restructuring the structure of the framework is a delicate task as React Native is also used internally, where we have yet another build system and dependency manager.
We need to make sure that all the changes we make for the OSS do not break the internal system and viceversa.

There just isn't much of reason for newer iOS sdks to support CocoaPods st this point since SPM ships with xcode, can work in conjunction with both Carthage and CocoaPods (assuming there aren't any duplicated dependencies requirements across the graphs), and is much more tightly integrated with the ecosystem. Our SDK is only going to support cocoa pods because we have many integrators in our space that use react native and we need to distribute a node module, but other teams may just forgo supporting at all.

I completely agree with this point, and we received the feedback also from other partners. The problem is slightly wider than this though.

We don't only use Cocoapods to install dependencies, but is also running some other tasks: it configures build flags to make sure that the project is properly configured and it runs some code generation tasks.
Of course, we can move both of these tasks to some script that SPM can invoke, especially now with the Xcode Plugins, but this is extra work that we need to plan for.

[chuckluck44]

@cipolleschi Thanks for the quick response. So the ImageManager example would actually work with its current folder structure. As the SPM Docs mention, its only swift and C-family languages that need to be separated:

Targets can contain Swift, Objective-C/C++, or C/C++ code, but an individual target can’t mix Swift with C-family languages. For example, a Swift package can have two targets, one that contains Objective-C, Objective-C++, and C code, and a second one that contains Swift code.

That being said, I have total respect for your teams current situation. Folder structure is obviously just a single aspect of migrating a project of this size/complexity. I only wanted to surface the fact that a majority of your mixed language issues may not be a problem anymore.

[cipolleschi]

@chuckluck44 Thank you for your suggestion and understanding. Improving the setup is on our radar. We really hope we would be able to prioritize it soon!

[ScottRobbins]

Fwiw, there is an open proposal about mixed language support here.

I suspect not much will gain traction for SPM until the fall, but it may be worth the RN team to review if this would achieve what they need when time allows.

[cipolleschi]

Thanks for the link! Will take a look as soon as I can!

[mfazekas]

FWIW there is an RFC to Cocapods repo to support SPM via cocoa pods.

See CocoaPods/CocoaPods#11942 and related PR: CocoaPods/Core#743