Relate receiver invariantly in method probe for Mode::Path

[compiler-errors]

Effectively reverts part of #126128
Fixes #126227

This PR changes method probing to use equality for fully path-based method lookup, and subtyping for receiver . method lookup.

r? lcnr

[lcnr]

should do a crater run for this

[compiler-errors]

@bors try

[bors]

⌛ Trying commit f4e027c with merge 774bd5b...

[bors]

☀️ Try build successful - checks-actions
Build commit: 774bd5b (774bd5ba31b89dab12d58c29690ad9f7e5c9f063)

[lcnr]

@craterbot check

[craterbot]

👌 Experiment pr-129073 created and queued.
🤖 Automatically detected try build 774bd5b
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-129073 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-129073 is completed!
📊 36 regressed and 5 fixed (500916 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[compiler-errors]

@craterbot check crates=https://crater-reports.s3.amazonaws.com/pr-129073/retry-regressed-list.txt p=1

[craterbot]

👌 Experiment pr-129073-1 created and queued.
🤖 Automatically detected try build 774bd5b
⚠️ Try build based on commit f4e027c, but latest commit is 14a5410. Did you forget to make a new try build?
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-129073-1 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-129073-1 is completed!
📊 0 regressed and 0 fixed (36 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[lcnr]

This PR changes path method lookup to use equality instead of subtyping, causing the following test to go from pass to fail. This does not cause any crater breakage and matches my expected behavior.

struct B<T>(T);

impl B<fn(&'static ())> {
    fn method(self) {
        println!("hey");
    }
}

fn foo(y: B<fn(&'static ())>) {
    B::<for<'a> fn(&'a ())>::method(y);
    //[with_this_change]~^ ERROR no function or associated item named `method` found
}

@compiler-errors you state that the existing behavior was introduced by #122317, however, the test case already compiled in previous versions: https://rust.godbolt.org/z/3bavf6rsT. Can you clarify what's going on there.

@rfcbot fcp merge

[rfcbot]

Team member @lcnr has proposed to merge this. The next step is review by the rest of the tagged team members:

• @BoxyUwU
• @compiler-errors
• @jackh726
• @lcnr
• @nikomatsakis
• @oli-obk
• @spastorino

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[compiler-errors]

@lcnr: Sorry. I thought that PR had caused the regression, but turns out that I had " fixed" it by making it eq then subsequently used sup because of regressions in . method dispatch: 8995c2c.

It was sup all along. So the state of the world before and after #122317 was the same, and the state of the world after this PR is objectively better.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[workingjubilee]

It seems that this sample code started compiling in 1.0, stopped compiling in 1.54, started compiling again in 1.63, and will stop compiling again in 1.83:
https://rust.godbolt.org/z/4bxY7Gr4j

[lcnr]

@bors r+

[bors]

📌 Commit 05483d5 has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit 05483d5 with merge e9e13a6...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing e9e13a6 to master...

[rust-timer]

Finished benchmarking commit (e9e13a6): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary 0.7%, secondary -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)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	2.8%	[2.8%, 2.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.9%	[-4.0%, -3.8%]	3
All ❌✅ (primary)	0.7%	[0.7%, 0.7%]	1

Cycles

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

Binary size

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

Bootstrap: 767.973s -> 767.732s (-0.03%)
Artifact size: 341.29 MiB -> 341.31 MiB (0.01%)