Enforce type of const param correctly in MIR typeck

[compiler-errors]

Properly intercepts and then annotates the type for a ConstKind::Param in the MIR.

This code should probably be cleaned up, it's kinda spaghetti, but no better structure really occurred to me when writing this case.

We could probably gate this behind the feature gate or add a fast path when the args have no free regions if perf is bad.

r? @BoxyUwU

[compiler-errors]

@bors try @rust-timer queue

[bors]

⌛ Trying commit c745d61 with merge f102e38...

[compiler-errors]

Forgor the stderr test, will push when try build is done.

[bors]

☀️ Try build successful - checks-actions
Build commit: f102e38 (f102e383e684e4400055503ebc792bf06fd2340c)

[rust-timer]

Finished benchmarking commit (f102e38): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results (primary 2.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.2%	[2.2%, 2.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.2%	[2.2%, 2.2%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 769.881s -> 768.249s (-0.21%)
Artifact size: 361.99 MiB -> 362.01 MiB (0.01%)

[BoxyUwU]

Can you add a test case that doesn't rely on generic_const_parameter_types too?

#![feature(adt_const_params, unsized_const_params)]

use std::marker::ConstParamTy_;

trait Trait<'a> {
    type Assoc: ConstParamTy_;
}

fn foo<'a, const N: <u8 as Trait<'static>>::Assoc>()
where
    for<'b> u8: Trait<'b>
{
    // Should error but doesn't on nightly
    let _: <u8 as Trait<'a>>::Assoc = N;
}

I don't think you can do it without unsized_const_params as you'd need a way to write a lifetime generic adt that's invariant over its lifetime parameter and also passes the builtin checks for ConstParamTy. If for<T> PhantomData<T>: ConstParamTy_ held then that'd be trivial to do but otherwise... 🤔

[compiler-errors]

Added a test with a fun trick to create a type that has invariant lifetimes but also is ConstParamTy lol

@rustbot ready

[BoxyUwU]

thx gamer, r=me if/when CI passes

[compiler-errors]

This will conflict with #138357. I'll rebase it in a bit.

@bors r-

[bors]

☔ The latest upstream changes (presumably #138416) made this pull request unmergeable. Please resolve the merge conflicts.

[compiler-errors]

@bors r=BoxyUwU rollup

[bors]

📌 Commit 0160c60 has been approved by BoxyUwU

It is now in the queue for this repository.