Don't try to label ObligationCauseCode::CompareImplItem for an RPITIT, since it has no name

[compiler-errors]

The old (current) trait solver has a limitation that when a where clause in param-env must be normalized using the same where clause, then we get spurious errors in normalize_param_env_or_error. I don't think there's an issue tracking it, but it's the root cause for many of the "fixed-by-next-solver" labeled issues.

Specifically, these errors may occur when checking predicate entailment of the GAT that comes out of desugaring RPITITs. Since we use ObligationCauseCode::CompareImplItem for these predicates, we try calling item_name on an RPITIT which fails, since the RPITIT has no name.

We simply suppress this logic when we're reporting a predicate entailment error for an RPITIT. RPITITs should never have predicate entailment errors, by construction, but they may due to this bug in the old solver.

Addresses the ICE in #127331, though doesn't fix the underlying issue (which is fundamental to the old solver).

r? types

[oli-obk]

Congradulences, you fixed an ICE 😆

r=me with crash test removed

[compiler-errors]

yeah im just gonna delete the test since it's not particularly interesting

[compiler-errors]

@bors r=oli-obk rollup

[bors]

📌 Commit d6276b3 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit d6276b3 with merge 9e27377...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 9e27377 to master...

[rust-timer]

Finished benchmarking commit (9e27377): comparison URL.

Overall result: ❌✅ regressions and 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)	0.4%	[0.4%, 0.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.4%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -1.2%)

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.8%, -0.5%]	5
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -0.5%)

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.4%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 699.359s -> 699.372s (0.00%)
Artifact size: 328.42 MiB -> 328.43 MiB (0.00%)