Add xcframework to ios out

[jmagman]

Description

Create Flutter.xcframework in the out/ios_* directories. It only contains the Flutter.framework in the same out directory, and will allow us to start testing XCFrameworks in the tool with --local-engine flags.

This doesn't publish Flutter.xcframework as a downloadable engine artifact.

Related Issues

Local engine support part of flutter/flutter#60109, which is a dependency to support macOS ARM simulators flutter/flutter#64502

Tests

Adopted the generated Flutter.xcframework in the Scenario app to prove it's working.

Checklist

• I read the [contributor guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [C++, Objective-C, Java style guides] for the engine.
• I read the [tree hygiene] wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Reviewer Checklist

• I have submitted any presubmit flakes in this PR using the [engine presubmit flakes form] before re-triggering the failure.

Breaking Change

Did any tests fail when you ran them? Please read [handling breaking changes].

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.

[gaaclarke]

LGTM I just had a few python nits, also I'd just make sure that --help works correctly. It would be nice to have a very simple test for create_xcframework.py

[gaaclarke]

nit: google python style guide requires some future imports:
https://google.github.io/styleguide/pyguide.html#from-__future__-imports

[jmagman]

Not sure what the minimum python version we support (I have 2.7.16 on my machine), I ran it through futurize.

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import argparse
import errno
import os
import shutil
import subprocess
import sys

This matches the other places we use from __future__ import
https://github.com/flutter/engine/blob/8f060b99547944606c9f5a7b1f0daea13b94f86e/build/copy_info_plist.py#L16-L23
https://github.com/flutter/engine/blob/b7e5940e3b1859a3dcd9aac86d3ac11770de8aac/build/git_revision.py#L7-L15

[gaaclarke]

nit: if !os.path.exists(output_dir)

[gaaclarke]

nit: typically list comprehensions are used for constructing lists, here you are constructing a list but ignoring the result. A for loop would be idiomatic python here.

[jmagman]

Thanks for the idiomatic tips, my python-foo is zero.

[jmagman]

It would be nice to have a very simple test for create_xcframework.py

@gaaclarke Can you point me to an existing example? The only one I see is ./tools/gn_test.py but I don't see where it's actually hooked up to run. Thanks for your help with this!

[gaaclarke]

I'm not sure there is an example for you. All tests are run through testing/run_tests.py, you'd want to add the execution of your test there. I didn't see an equivalent test in there already. Even just running it through a linter would be better than nothing, just to make sure its has valid python code in it.

[jmagman]

Even just running it through a linter would be better than nothing, just to make sure its has valid python code in it.

Created flutter/flutter#70654.

[jmagman]

I'm not sure there is an example for you.

Scenarios.app won't build if the Flutter.xcframework is missing. That's about the same coverage we had with any of the other framework build subscripts, like install_framework_headers.py.

[gaaclarke]

lgtm!