Add a fully fledged Clause type, rename old Clause to ClauseKind

[compiler-errors]

Does two basic things before I put up a more delicate set of PRs (along the lines of #112714, but hopefully much cleaner) that migrate existing usages of ty::Predicate to ty::Clause (predicates_of/item_bounds/ParamEnv::caller_bounds).

1. Rename Clause to ClauseKind, so it's parallel with PredicateKind.
2. Add a new Clause type which is parallel to Predicate.
   • This type exposes Clause::kind(self) -> Binder<'tcx, ClauseKind<'tcx>> which is parallel to Predicate::kind 😸

The new Clause type essentially acts as a newtype wrapper around Predicate that asserts that it is specifically a PredicateKind::Clause. Turns out from experimentation¹ that this is not negative performance-wise, which is wonderful, since this a much simpler design than something that requires encoding the discriminant into the alignment bits of a predicate kind, or something else like that...

r? @lcnr or @oli-obk

Footnotes

1. https://github.com/rust-lang/rust/pull/112714#issuecomment-1595653910 ↩

[rustbot]

Some changes occurred in const_evaluatable.rs

cc @BoxyUwU

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[lcnr]

r=me after nits

[lcnr]

this assert is perf critical? and assuming that it is, would it not be faster to make this an assert and make using the clause use unreachable_unchecked?

[compiler-errors]

I don't think it's perf critical, just seems redundant since we already assert that it's a Clause in Clause::kind.

[compiler-errors]

Anyways I made it an assert, and we can make it unreachable_unchecked on the read path if perf warrants it later.

[oli-obk]

What's your opinion on reexporting the ClauseKind variants from a clause module and using clause::Trait instead?

[compiler-errors]

Eh, doesn't really seem worthwhile tbh. Or at least, I think I want to do it as a follow-up 😸

[bors]

☔ The latest upstream changes (presumably #112351) made this pull request unmergeable. Please resolve the merge conflicts.

[oli-obk]

@bors r=lcnr

[bors]

📌 Commit dcee3ab has been approved by lcnr

It is now in the queue for this repository.