"Stabilizable" prototype for expanded const generics

[nikomatsakis]

Metadata
Owner(s)	@BoxyUwU
Team(s)	lang, types
Goal document	2024h2/min_generic_const_arguments

Summary

Experiment with a new min_generic_const_args implementation to address challenges found with the existing approach. The design for min_generic_const_args is outlined in this document written by @BoxyUwU

Tasks and status

• Discussion and moral support (lang, types )
• Implementation and mentoring (@BoxyUwU)
• Implementation (@camelid)
• Reviewer (@compiler-errors)

[nikomatsakis]

This issue is intended for status updates only.

For general questions or comments, please contact the owner(s) directly.

[BoxyUwU]

Key Developments: #125915 landed which is necessary to start implementation work on min_generic_const_args, a draft outlining the ideas behind the proposed feature has also been written
Blockers: no
Help Wanted: not currently in need of anything

[BoxyUwU]

The past ~month has been spent figuring out some implementation constraints arising from DefId creation of anon consts. My time has also been somewhat diverted to other things though that should have cleared up now :-)

[BoxyUwU]

camlid has started working on using the new lowering schema for more than just const parameters which once done will allow us to introduce a min_generic_const_args feature gate. compiler-errors has been working on removing the eval_x methods on Const that do not perform proper normalization and are incompatible with this feature

[BoxyUwU]

min_generic_const_args now exists as a feature gate (though without any functionality only some gated refactorings), shouldn't be long before it has actual functionality behind it 🤞 The refactoring to remove all the eval_x methods on ty::Const has been completed so it will now be possible to correctly implement normalization for constants.