Meta issue for implementation of overriding fields in strong mode

[mit-mit]

Strong mode needs to support overriding a field in a subclass. This meta-issue tracks that.

Blocking implementation issues:

• DDC, support override with @virtual: Support @virtual annotation on fields in DDC #27385
• Analyzer, support new mixin restrictions, Strong mode: Disallow private collisions induced via mixin #28809
• DDC, always assume field overrides: Support overriding fields in DDC #28119
• Analyzer, remove current restriction: Analyzer, support overriding fields in strong mode #28120 (blocked on Support overriding fields in DDC #28119)
• Make sure changelog has an entry for this

Specification work:

• Informal specification for new mixin restrictions
• Specify if we have @sealed or not (current draft)
• Specify any additional restrictions on field/field overrides: Flag unintended field over field overrides #28810
• Full specification (if needed, i.e. if anything changes from the current language)

Cleanup tasks:

• Desupport @virtual annotation support on fields (see Stop supporting '@virtual' annotation on fields to allow field overrides in strong mode #28589)

[leafpetersen]

This is blocked on finding an implementation strategy that works for DDC, and/or specifying a subset of the feature which can be supported in DDC.