Tracking Issue for Generic Constant Arguments MVP

[camelid]

This is a tracking issue for the prototype described in rust-lang/rust-project-goals#100. Background reading as to the design/justification for this feature.
The feature gate for the issue is #![feature(min_generic_const_args)].

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Add ConstArgKind::Path (Represent type-level consts with new-and-improved hir::ConstArg #125915)
• Use ConstArgKind::Path for all single-segment paths (Use ConstArgKind::Path for all single-segment paths, not just params under min_generic_const_args #131081)
• Use ConstArgKind::Path for all paths
  • most paths mgca: Lower all const paths as ConstArgKind::Path #135186
  • Support ConstArgKind::Path for uses of static paths #132986
• Support "simple" exprs necessary for constructing adt_const_params types:
  • Struct construction exprs, e.g. Some(N), Adt { field: N } Support ConstArgKind::Paths for const struct/variant constructors #132985
  • Array exprs, e.g. [M; N], [1, 2, N]
  • Tuple exprs, (10, N)
• Make inherent associated constants behave correctly
• Implement type system normalization that makes use of associated_const_equality bounds
• Merge feature(associated_const_equality) into min_generic_const_args
• Traits are dyn compatible if all associated consts are type safe
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

TODO

Implementation history

• Initial document proposing the design/feature hackmd link
• Represent type-level consts with new-and-improved hir::ConstArg #125915
• Fix anon const def-creation when macros are involved #129137
• Use ConstArgKind::Path for all single-segment paths, not just params under min_generic_const_args #131081
• Encode MIR for const ctors in metadata and allow eval for them #134873
• mgca: Lower all const paths as ConstArgKind::Path #135186