Apply dart fixes to mixins

[Piinks]

Looking at TextSelectionDelegate, it is a mixin, so writing a fix for a deprecated member is not very clear.
I think I can write a fix for all the classes that use the mixin, but that could result in a large number of rules to write for a single mixin.
Being able to target and test mixins could streamline the process if possible. :)

[srawlins]

cc @bwilkerson

[asashour]

I guess this is data-driven-fix and not a normal quick fix.

If so, inMixin is there.

Could you please provide a minimal case if this is still valid?

[Piinks]

For sure, just ran into this today. There is a deprecated method in WidgetInspectorService, which is a mixin. I wrote the following rule:

  - title: "Migrate to addPubRootDirectories"
    date: 2023-11-29
    element:
      uris: ['widgets.dart', 'material.dart', 'cupertino.dart']
      method: 'setPubRootDirectories'
      inMixin: 'WidgetInspectorService'
    changes:
      - kind: 'rename'
        newName: 'addPubRootDirectories'

with the expectation it would result in this transformation:

// Before
  class Test with WidgetInspectorService {
    Test();
  }
  final Test test = Test();
  test.setPubRootDirectories([]);

// After
  class Test with WidgetInspectorService {
    Test();
  }
  final Test test = Test();
  test.addPubRootDirectories([]);

This does not work. Am I holding it wrong? :)

[Piinks]

For reference, came up in flutter/flutter#139257

[bwilkerson]

It looks right to me. Probably another unimplemented part of the API.