JavaScript compilers support for --null-assertions in Dart 3.0

[nshahan]

Regarding the --null-assertions flag. It provides enhanced null safety errors when running without sound null safety. It was added as a tool to assist in large scale migrations so you can migrate a library and get some null safety errors at runtime when testing an app that isn't fully migrated. I believe this feature is considered totally obsolete in a world where all code being compiled should be null safe.

For DDC this is a question of what flags are supported when you try to run a debug app with package:webdev or flutter web. For dart2js it includes those and what flags are available through dart compile js.

cc @sigmundch @jakemac53 @fishythefish @mit-mit @itsjustkevin

[jakemac53]

dart-lang/build#3424 drops support for this flag in build_runner so we won't pass it to the compilers any more (specifically kernel, ddc, and dart2js).

[nshahan]

Just waiting on the unsound null safety flags to be removed from Flutter tool.

[mit-mit]

@nshahan is there a tracking issue for the Flutter tool flag issue?

[nshahan]

@mit-mit yes the flag handling cleanup got rolled into flutter/flutter#118810.

[nshahan]

Closing this issue because no more work is needed in the SDK but we ware still depending on the flag cleanup in Flutter Tools:

• Remove option to pass unsound null safety flag in flutter build/run commands flutter/flutter#118810