Fix trait solver overflow with non_local_definitions lint

[Urgau]

This PR fixes the trait solver overflow with the non_local_definitions lint reported in #123573 using the suggestion from @lcnr: #123573 (comment) to use the next trait solver.

I have not (yet) tried to create a minimized repro @compiler-errors did the minimization (thanks you) but I have manually tested on the starlark-rust project that it fixes the issue.

Fixes #123573
r? @lcnr

[compiler-errors]

I think I minimized a test:

pub trait Test {}

impl<'a, T: 'a> Test for &[T] where &'a T: Test {}

fn main() {
    struct Local {}
    impl Test for &Local {}
}

[lcnr]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 5250336 with merge fff3bb1...

[bors]

☀️ Try build successful - checks-actions
Build commit: fff3bb1 (fff3bb18bd7c4c92cf9f277dffa7ff824422aa52)

[rust-timer]

Finished benchmarking commit (fff3bb1): comparison URL.

Overall result: ❌ regressions - 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 is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Max RSS (memory usage)

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

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: 667.477s -> 665.775s (-0.25%)
Artifact size: 318.52 MiB -> 318.75 MiB (0.07%)

[lcnr]

cc @rust-lang/types. this PR changes a lint to always use the new trait solver by default to avoid errors from fatal overflow with the old solver.

This lint always runs in an empty environment and does not use generic params. It therefore does not rely on any additional behavior not required for -Ztrait-solver=next which is getting stabilized separately. Given that it's a lint it is also not stability or soundness relevant.

[lcnr]

Going to start a types FCP to officially state that going forward, the @rust-lang/initiative-trait-system-refactor has the authority to enable the use of the new solver on stable without FCPs as long as t-types is pinged in the PR and the affected area is neither relevant for soundness nor backwards compatibility.

@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
• @aliemjay
• @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.

[bors]

☔ The latest upstream changes (presumably #123676) made this pull request unmergeable. Please resolve the merge conflicts.

[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.

[lcnr]

@bors r+

[bors]

📌 Commit c2e2245 has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit c2e2245 with merge f22a0c2...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing f22a0c2 to master...

[rust-timer]

Finished benchmarking commit (f22a0c2): comparison URL.

Overall result: ❌ regressions - 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)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	1

Max RSS (memory usage)

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

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: 671.849s -> 669.682s (-0.32%)
Artifact size: 315.25 MiB -> 315.52 MiB (0.08%)