Implement std::marker::Tuple, use it in extern "rust-call" and Fn-family traits

[compiler-errors]

Implements rust-lang/compiler-team#537

I made a few opinionated decisions in this implementation, specifically:

1. Enforcing extern "rust-call" on fn items during wfcheck,
2. Enforcing this for all functions (not just ones that have bodies),
3. Gating this Tuple marker trait behind its own feature, instead of grouping it into (e.g.) unboxed_closures.

Still needing to be done:

1. Enforce that extern "rust-call" fn-ptrs are well-formed only if they have 1/2 args and the second one implements Tuple. (Doing this would fix ICE in ICE when transmuting to extern "rust-call" fn() #66696.)
2. Deny all explicit/user impls of the Tuple trait, kinda like Sized.
3. Fixing Tuple trait built-in impl for chalk, so that chalkification tests are un-broken.

Open questions:

1. Does this need t-lang or t-libs signoff?

Fixes #99820

[rustbot]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

• Stabilizing library features
• Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
• Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
• Changing public documentation in ways that create new stability guarantees
• Changing observable runtime behavior of library APIs

[rust-highfive]

r? @thomcc

(rust-highfive has picked a reviewer for you, use r? to override)

[compiler-errors]

r? compiler

[bors]

☔ The latest upstream changes (presumably #99948) made this pull request unmergeable. Please resolve the merge conflicts.

[joshtriplett]

This does need @rust-lang/libs-api and @rust-lang/lang review, but as long as all of it is still marked unstable, I don't think it needs an FCP.

For my part, 👍 for lang and for libs-api, for the proposed surface area. Others should chime in as well if they have thoughts or concerns, though.

[jackh726]

Can we split this into parts? First part is just adding the Tuple trait and implementing it?

[compiler-errors]

blocking on landing that other one

[cjgillot]

Will this also fix the ICE in #57404?

[cjgillot]

This span is weird.

[compiler-errors]

I think we could probably pass the arg span into the obligation cause or something to make this better

[cjgillot]

Could we keep the def_span here?

[compiler-errors]

yeah I think so

[compiler-errors]

Will this also fix the ICE in #57404?

Yes, just checked.

[compiler-errors]

@cjgillot with this PR, that issue now reports:

error[E0277]: `&mut ()` is not a tuple
   --> /home/gh-compiler-errors/test.rs:6:41
    |
6   |     handlers.unwrap().as_mut().call_mut(&mut ());
    |                                -------- -^^^^^^
    |                                |        |
    |                                |        `&mut ()` is not a tuple
    |                                |        help: consider removing the leading `&`-reference
    |                                required by a bound introduced by this call
    |
    = help: the trait `Tuple` is not implemented for `&mut ()`
note: required by a bound in `call_mut`
   --> /home/gh-compiler-errors/rust/library/core/src/ops/function.rs:334:23
    |
334 | pub trait FnMut<Args: Tuple>: FnOnce<Args> {
    |                       ^^^^^ required by this bound in `call_mut`

error: aborting due to previous error

instead of ICEing.

[crlf0710]

Now that #100251 has landed, seems this is now unblocked.

[compiler-errors]

@bors try

[bors]

⌛ Trying commit 52655b8d45d36b35cf6b3bcc0174f7aa45406255 with merge 388b725dea7416978ab58ab1f908139d530308a7...

[jackh726]

@bors r+ rollup=never

[bors]

📌 Commit ff8f84c has been approved by jackh726

It is now in the queue for this repository.

[bors]

⌛ Testing commit ff8f84c with merge 7eef946...

[bors]

☀️ Test successful - checks-actions
Approved by: jackh726
Pushing 7eef946 to master...

[rust-timer]

Finished benchmarking commit (7eef946): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.1%	[-1.4%, -0.6%]	3
Improvements ✅ (secondary)	-3.0%	[-4.0%, -0.4%]	7
All ❌✅ (primary)	-1.1%	[-1.4%, -0.6%]	3

Max RSS (memory usage)

Results

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)	1.5%	[0.6%, 2.5%]	2
Regressions ❌ (secondary)	2.3%	[2.2%, 2.3%]	2
Improvements ✅ (primary)	-1.0%	[-1.6%, -0.5%]	2
Improvements ✅ (secondary)	-5.5%	[-5.5%, -5.5%]	1
All ❌✅ (primary)	0.2%	[-1.6%, 2.5%]	4

Cycles

Results

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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	4.6%	[4.6%, 4.6%]	1
Improvements ✅ (primary)	-0.5%	[-0.5%, -0.5%]	1
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	0.0%	[-0.5%, 0.5%]	2

[Mark-Simulacrum]

Delta here appears to be noise (but is an improvement anyway).