Define "dart.library.mirrors" and "dart.library.isolate" as false in dartdevc

[munificent]

Since Dart 2.0 does not support those libraries on the web (#30538), the fromEnvironment() flags for those should return false.

[jmesserly]

I discovered that dart:html and dart:io import dart:isolate.

HTML only exists in dart4web, so we can remove that dependency and refactor APIs that use it.
dart:io is importable, but throws on dart4web. I'm not sure if we want dart:isolate imports to be an error at compile time, or an error at runtime. Advice? @vsmenon

See also #32293 (disable dart:isolate in DDC)

[vsmenon]

I was thinking compile time error. @sigmundch @kevmoo is that consistent with your understanding?

[kevmoo]

🤷‍♂️

[sigmundch]

Agree it should be a compile-time error.

It seems like the only API that uses dart:isolate from dart:html is spawnDomUri.

However, I don't believe we can ban importing dart:io at this time. That is currently needed to support package:http for a bit longer (we had to go out of our way to allow it in dart2js temporarily). Two ideas come to mind:

• change the dart:io implementation entirely for dart4web to make it super lean and only expose what pacakge:http needs
• temporarily use a whitelist to allow importing dart:isolate from dart:* libraries (practically treating it like if it were an internal dart:_isolate library).

I currently prefer the latter. We could also do the latter by introducing an actual dart:_isolate library, reexporting it from dart:isolate, and change dart:io and dart:html to import the internal. Then we can unconditionally make it invalid to import the public dart:isolate library.

Thoughts?

[jmesserly]

Yeah, dart:html is very easy to fix (change Future<SendPort> to Future for a method that throws an unimplemented error anyways :)

I think I have a fix for dart:io as well. It turned out the only usage was SendPort, for one unused field, and one private class/private method for the VM. I have removed it from the API signature of that private class in dart:io. Testing it out now. :)

[jmesserly]

https://dart-review.googlesource.com/c/sdk/+/48885