ios - #if canImport() does not find frameworks with CocoaPods

Question

Hello here is our Podspec which has a default_subspec and an optional subspec (which won't be taken since the default is already set). That subspec has more features, but takes an additional 8MB of size...

`s.default_subspec = 'mainSDK'

s.subspec 'mainSDK' do |mainSDK|
mainSDK.vendored_frameworks = 'mainSDK.framework'
mainSDK.source_files = "mainSDK.framework/Headers/*.h"
end

s.subspec 'additionalSDK' do |additionalSDK|
additionalSDK.source_files = "additionalSDK.framework/Headers/*.h"
additionalSDK.vendored_frameworks =['additionalSDK.framework', 'mainSDK.framework']
end

Now, in our mainSDK we include additionalSDK with #if canImport(additionalSDK) We then provide code related to additionalSDK in between those compiler flags, like this:

#if canImport(additionalSDK)
    //adding optional delegate
    class ViewController: UIViewController, OptionalDelagate
#else
    //no need for delagete
? ? class ViewController: UIViewController
#endif

However, after client integrates our mainSDK he sees that this framework is missing module: additionalSDK.framework

How is this possible? We have marked additionalSDK as optional in our workspace. We have tried to set additionalSDK as a -weak_framework in other linker flags(Build settings) , but this did not helped.

If client integrates additionalSDK everything works well, because all frameworks are linked..

​ Optional dependencies, without CocoaPods work well, it is just problem of CocoaPods or I don't know how to configure it

s.platform = :ios
s.ios.deployment_target = '9.0'
s.name = "mainSDK"
s.summary = "mainSDK IOS SDK"
s.requires_arc = true

# 2
s.version = "1.0.8.6.5"

s.source = { :http => "https://s3-eu-west-1.amazonaws.com/zipOfSDK.zip"}
s.framework = "UIKit"

s.source_files = "mainSDK.framework/Headers/*.h"

s.default_subspec = 'mainSDK'

s.subspec 'mainSDK' do |mainSDK|
mainSDK.vendored_frameworks = 'mainSDK.framework'
mainSDK.source_files = "mainSDK.framework/Headers/*.h"
end

s.subspec 'additionalSDK' do |additionalSDK|
additionalSDK.source_files = "additionalSDK.framework/Headers/*.h"
additionalSDK.vendored_frameworks =['additionalSDK.framework', 'mainSDK.framework']
end

s.swift_version = "4.2"

end

Answer 1

Short answer: Using #if canImport(Module) would not allow you to achieve what you described in a closed source setup. I see some misunderstanding of how this conditional compilation works.

What I mean is that you've already built a framework. Seems that #if canImport is resolved at a compile time, so it is not dynamic.

When you use already prebuilt mainSDK.framework, the part #if canImport(additionalSDK) was already evaluated. And the result depends on the availability of 'additionalSDK' in the build chain, when it was built (so on your machine when you prepare it for shipping to clients), not when it is linked.

I found someone struggling with a similar issue here: https://flint.tools/blog/finding-a-weak-linking-solution.html

The good news is, that what you want to achieve is possible using weak linking and objective-C interoperability.

I'm working on a short article about the topic, in the meantime, here is an example repository with a working setup, similar to what you described as requirements:

https://github.com/amichnia/Swift-framework-with-optional-frameworks

It supports:

• AdditionalSDK is optional
• MainSDK have classes adopting AdditionalSDK's protocols
• MainSDK knows if additional features are available
• It is all in closed source setup

Update:

I finished an article, which should describe the solution in more details. It is available at https://medium.com/@amichnia_31596/create-a-mostly-swift-framework-with-optional-features-7e8a9ac960f9