[DONT MERGE] externally implementable items

[jdonszelmann]

Supersedes #140010
Tracking issue: #125418

Getting started:

#![feature(eii)]

#[eii(eii1)]
pub fn decl1(x: u64) 
// body optional (it's the default)
{
    println!("default {x}");
}

// in another crate, maybe
#[eii1]
pub fn decl2(x: u64) {
    println!("explicit {x}");
}

fn main() {
    decl1(4);
}

[jdonszelmann]

TODO: do we need this:

• option 1: we do and implement our own reachability analysis based on it separate from RUSTC_STD_INTERNAL_SYMBOL.
• option 2: we don't cause we also use RUSTC_STD_INTERNAL_SYMBOL on all EIIs. In that case we should rename STD_INTERNAL_SYMBOL
• option 3: same as option 2 but maybe we shouldn't use RUSTC_STD_INTERNAL_SYMBOL in the first place; we leave it as-is and create a new flag thta's like it but specifically for EIIs and named something else like RUSTC_USED_BY_NONDIRECT_DEP_CRATE or whatever nicer name we can think of that (as long as it doesn't use STD since it's not really specific to that anymore)

[jdonszelmann]

despite STD_INTERNAL_SYMBOL working, and we can test with it for a bit, this is not the way we should do it. i.e. not option 2.

[jdonszelmann]

It took me a little bit to decide what is the expected behavior here. We might want to remove this warning. Defaults are in some way expected to be unused. However, here we can prove it because the explicit impl is in the same crate hence the warning.

[jdonszelmann]

removing the warning actually makes the code a tiny bit trickier

[jdonszelmann]

@bors2 try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: d5a6633 (d5a66337e06d3b77a1ab8f6793055535195c3ae9, parent: 364da5d88d772fa40fb20353443595385443ac25)

[rust-timer]

Finished benchmarking commit (d5a6633): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.1%, 1.5%]	19
Regressions ❌ (secondary)	0.4%	[0.1%, 1.0%]	44
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	4
All ❌✅ (primary)	0.3%	[0.1%, 1.5%]	19

Max RSS (memory usage)

Results (primary 1.7%, secondary 3.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.7%	[0.6%, 2.3%]	6
Regressions ❌ (secondary)	4.7%	[1.1%, 11.2%]	16
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.9%, -1.2%]	2
All ❌✅ (primary)	1.7%	[0.6%, 2.3%]	6

Cycles

Results (primary 3.1%, secondary -1.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.1%	[3.1%, 3.1%]	1
Regressions ❌ (secondary)	3.2%	[2.5%, 3.6%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-4.1%, -2.0%]	9
All ❌✅ (primary)	3.1%	[3.1%, 3.1%]	1

Binary size

Results (primary 0.0%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	93
Regressions ❌ (secondary)	0.1%	[0.0%, 0.3%]	61
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	93

Bootstrap: 468.052s -> 471.14s (0.66%)
Artifact size: 387.52 MiB -> 390.25 MiB (0.71%)

[jdonszelmann]

Well, shit. I think I know some fixes but I hoped this wouldn't happen

[lcnr]

please change the structure of the file to

• soundness critical functions in some decent order
• diagnostics stuff

View changes since this review

[bors]

☔ The latest upstream changes (presumably #145881) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #146666) made this pull request unmergeable. Please resolve the merge conflicts.

[lcnr]

Output -> Error

[lcnr]

Suggested change

	) -> Option<CheckRegionBoundsOnItemOutput> {
	) -> Result<(), CheckRegionBoundsOnItemError> {

also... is check_region_bounds_on_item🤔 it's really just check_number_of_early_bound_regions, is it not?

[lcnr]

Suggested change

	/// checks whether the signature of some `external_impl`, matches
	/// Checks whether the signature of some `external_impl`, matches

[lcnr]

we're not actually computing implied bounds here xd

Either change the FIXME to state that we're not computing implied bounds, or start computing the implied bounds. Also make sure all the comments here talk about "declaration" and "external_impl" instead of trait vs impl

[lcnr]

hmm, it would be kinda cool to go

    if declaration_number_args == external_impl_number_args {
        Ok(())
    } else {
        Err(report_number_of_method_arguments_mismatch(...))
    }