Flutter runtime: fix varying Podfile.lock checksums by using standard pod target dir for HEADER_SEARCH_PATHS

[andeart]

Issue: The current .podspec files (for both iOS and macOS) define the HEADER_SEARCH_PATHS using __dir__. There is nothing wrong with this in isolation. On running pod install in a Spine-dependent Flutter project, this generates the Local Podspecs/spine_flutter.podspec.json file with the HEADER_SEARCH_PATHS value containing a path specific to that machine/environment. For example, if I ran this locally for a Flutter iOS project, it would result in:

"HEADER_SEARCH_PATHS": "\"Users/andeart/my_flutter_project/ios/.symlinks/plugins/spine_flutter/ios/Classes/spine-cpp/include\""

This is still harmless in isolation as this file is typically inside a gitignored directory for the Flutter project, and so (in theory) should not matter that it contains values specific to the developer's environment.

However, because of this machine/environment-specific value, the Flutter project's ios/Podfile.lock file now contains a spine_flutter spec-checksum entry that varies per developer/environment. This is an issue on shared Flutter projects because the Podfile.lock files are usually added to source control.

In other words, due to the nature of the current HEADER_SEARCH_PATHS assignment, every cloner of the Spine-dependent Flutter repo will end up with a different spine_flutter spec-checksum entry in their ios/Podfile.lock file, leading to source-control hassles or repeated overwrites of the same file without any dependency changes to explain it.

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Solution: By using the officially defined PODS_TARGET_SRCROOT variable from the CocoaPods spec, the generated spine_flutter.podspec.json gets generated with a HEADER_SEARCH_PATHS value that is not specific to that machine/environment, and (importantly) still points to the same location of the expected spine-cpp directory within that Flutter project's iOS plugins. Consequently, even after running pod install, the spec-checksum of the spine_flutter entry in ios/Podfile.lock remains constant across machines/environments, as we might expect if the Spine dependency isn't actually being modified.

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Additional context: I gave this update a test with fresh clones across multiple machines and the checksum value in the Podfile.lock files now remains consistent across multiple machines, for both iOS and macOS.

Let me know if I missed anything please. Thanks for creating this useful runtime!

[badlogic]

Oh, this is great! I'm not enough of a Cocoapods expert, so I went with the simplest solution. This is much better. Thanks!

[andeart]

@badlogic Happy to help! And thanks for the approval. Do you have an idea of when we can expect a release containing this update please?

[badlogic]

@andeart apologies, had to get a few C++ side fixes in as well. I just released 4.2.32 to pub.dev. Should be live in a few minutes.

Thanks for your contribution!

[andeart]

I appreciate the quick update @badlogic !