Remove nullOk in MediaQuery.of

[gspencergoog]

Description

Adds MediaQuery.maybeOf to replace calling MediaQuery.of(context, nullOk: true), and removes the nullOk parameter. Also changes MediaQuery.of to return a non-nullable value, and removes many instances of the ! operator, reducing the possible places where a null dereference could occur.

Related Issues

• Some widgets' nullOk parameters are inconsistently applied. #68637

Tests

• No tests were harmed in the making of this PR.
• Added a test to make sure that maybeOf works as expected, updated test output for media_query_test.dart and others.

Breaking Change

• Yes, this is a breaking change that will require a migration guide.
  • I wrote a design doc.

[goderbauer]

Changes LGTM. Since this is failing google3 I would argue that this is a breaking change, though, and we should probably publish a quick migration guide.

[gspencergoog]

I agree, I'll work on the guide.

[goderbauer]

@bwilkerson This would be another great use case for a flutter fix that automatically migrates user code.

[gspencergoog]

Here's the design doc for the migration.

Writing the migration guide itself next.

[gspencergoog]

OK, I just removed the nullOk entirely, since I don't like the fact that we're avoiding a compile time check in order to fail at runtime: that's a much more error-prone failure mode, and will definitely surprise people: I'd rather it just fail to compile.

[Hixie]

It's a pity we lose the analyzer warning that way.

[goderbauer]

LGTM

[gspencergoog]

@Hixie Well, we lose the analyzer warning, but gain a compiler error. I agree, is a pity that there's no way to say "Fail to compile, but give a custom message like a deprecation" for when someone uses a removed parameter.

Hopefully the docs at the site are clear enough that they'll understand what to do when they get the compiler error.

[Hixie]

Might be worth following up with @leafpetersen to see if we can change Dart in some way in the future to make this kind of thing better.

[gspencergoog]

OK, I submitted dart-lang/sdk#43942 as a feature request.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite Mac framework_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite Mac framework_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.