Use `jnigen` and `ffigen` to call Java/Kotlin/Swift/ObjC natively without the `MethodChannels`

[marandaneto]

Description

https://dart.dev/guides/libraries/java-interop and https://dart.dev/guides/libraries/objective-c-interop
Depends on Dart 3, still experimental.
Can probably use gen packages (ffigen) for Linux, Windows, etc.
Need to figure out how to call Web without MethodChannels

[ueman]

For web you don't need any method channels or similar since Dart has JS interopt built-in: https://dart.dev/web/js-interop

[vaind]

1. We may need to do this to enable profiling. Starting a profiler via a method channel is an async operation (even though the actual profiler startup call in objective-c/swift is synchronous). However, Hub.startTransaction() is synchronous so we cannot wait for the profiler to be actually started before returning from this function.
2. I don't see why this would be limited to Dart 3, considering it seems to use standard FFI which has been around forever. Do you remember the source for that SDK version limitation @marandaneto?

[ueman]

ffigen for Swift was introduced in Dart 2.18 which shipped with Flutter 3.3, see https://medium.com/flutter/announcing-flutter-3-3-at-flutter-vikings-6f213e068793

Then there's dart:ffi (which is part of the Dart SDK), and package:ffi (distributed via pub). ffigen makes use of a specific version of package:ffi. ffigen is also the tool where most of the Swift binding magic and its improvments happens.

In addition to that, Swift ffi is considered experimental, however cupertino_http (a package using those Swfit/objc bindings) is considered stable.

[vaind]

Looking at the wording in the Dart 2.18 announcement, it looks like it's just a documentation issue (and the availability of a generator), not that it didn't work with an older version of the SDK. The changelog for 2.18 doesn't mention anything (or I'm blind) so that would indicate my assumption may be true.
I may be wrong but I think we wouldn't even need to bump the minimum Dart version in pubspec. Anyway, I'll likely give this a quick try, considering the need for profiling I've mentioned above.

(FYI, I am pretty familiar with FFI: https://github.com/objectbox/objectbox-dart/graphs/contributors - the whole thing is based on a C(++) library)

[marandaneto]

@vaind I read somewhere about min Dart 3 but I don't recall where exactly, it could be a docs issue so go ahead and try it out.