Regenerate FlutterMacOS.xcframework when sources of dependencies change

[vashworth]

Fixes flutter/flutter#144716.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[jmagman]

Since _generate_symlinks_and_verify_framework_module deps on _generate_symlinks which deps on this same list, it seems like maybe the deps aren't the source of the problem. Maybe sources = [ $root_build_dir/$_flutter_framework_name.stamp ] would make this re-run if the framework is rebuilt?

@zanderso what's the gn idiomatic way to do this?

[zanderso]

I believe the right way to do this is to leave this deps list unchanged, but to make _generate_symlinks a public_deps of _generate_symlinks_and_verify_framework_module. (I think that's all that should be needed, but making the deps of _generate_symlinks be public_deps in addition would be the next thing to try.)

[vashworth]

Unfortunately setting deps to public_deps for both _generate_symlinks and _generate_symlinks_and_verify_framework_module didn't work, perhaps because _generate_symlinks_and_verify_framework_module is a shared_library?

Looking at how we do this for iOS, we have the flutter_framework depend on a group universal_flutter_framework, which then has a dependency on the shared_library (copy_and_verify_framework_module) and the other deps

engine/shell/platform/darwin/ios/BUILD.gn

Lines 448 to 478 in 76f33eb

	group("universal_flutter_framework") {
	visibility = [ ":*" ]
	deps = [
	":copy_and_verify_framework_module",
	":copy_dylib",
	":copy_framework_icu",
	":copy_framework_info_plist",
	":copy_framework_module_map",
	":copy_framework_privacy_manifest",
	":copy_license",
	]
	if (is_asan) {
	deps += [ ":copy_asan_runtime_dylib" ]
	}
	}
	action("flutter_framework") {
	script = "//flutter/sky/tools/create_xcframework.py"
	outputs = [ "$root_out_dir/Flutter.xcframework" ]
	args = [
	"--frameworks",
	rebase_path("$_flutter_framework_dir"),
	"--name",
	"Flutter",
	"--location",
	rebase_path("$root_out_dir"),
	]
	deps = [ ":universal_flutter_framework" ]
	}

I could add a group to the macOS version to mimic it, also perhaps instead of the deps from _generate_symlinks, just use _generate_symlinks as the dep. What do you think?

[vashworth]

@jmagman @zanderso friendly ping

[zanderso]

Shucks. The sematics of GN deps and when thy block and when they propagate are certainly confusing. If there's a working pattern on the macOS side, then mimicking that here makes sense to me.

[jmagman]

RSLGTM to whatever @zanderso approves.