Restrict recursive opaque type check

[compiler-errors]

We have a recursive opaque check in writeback to avoid inferring the hidden of an opaque type to be itself:

rust/compiler/rustc_hir_typeck/src/writeback.rs

Lines 556 to 575 in 33a2c24

	struct RecursionChecker {
	def_id: LocalDefId,
	}
	impl<'tcx> ty::TypeVisitor<TyCtxt<'tcx>> for RecursionChecker {
	type BreakTy = ();
	fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
	if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) = *t.kind() {
	if def_id == self.def_id.to_def_id() {
	return ControlFlow::Break(());
	}
	}
	t.super_visit_with(self)
	}
	}
	if hidden_type
	.visit_with(&mut RecursionChecker { def_id: opaque_type_key.def_id })
	.is_break()
	{
	continue;
	}

Issue #113619 treats make_option2 as not defining the TAIT TestImpl since it is inferred to have the definition TestImpl := B<TestImpl>, which fails this check. This regressed in #102700 (5d15beb), I think due to the refactoring that made us record the hidden types of TAITs during writeback.

However, nothing actually seems to go bad if we relax this recursion checker to only check for directly recursive definitions. This PR fixes #113619 by changing this recursive check from being a visitor to just checking that the hidden type is exactly the same as the opaque being inferred.

Alternatively, we may be able to fix #113619 by restricting this recursion check only to RPITs/async fns. It seems to only be possible to use misuse the recursion check to cause ICEs for TAITs (though I didn't try too hard to create a bad RPIT example... may be possible, actually.)

r? @oli-obk

--

Fixes #113314

[compiler-errors]

@bors try

[bors]

⌛ Trying commit 0871d66e463572a466d36634f9993526c7dd80dc with merge 168adca86021b4acdae9e717a4c09015b0f1062f...

[compiler-errors]

@bors try

[bors]

⌛ Trying commit 5e179f7364488f069858d7bda7259aba7f42a526 with merge 1066537ce94b83c04b9e840838af0b66b0ef1500...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1066537ce94b83c04b9e840838af0b66b0ef1500 (1066537ce94b83c04b9e840838af0b66b0ef1500)

[compiler-errors]

@craterbot check

[craterbot]

👌 Experiment pr-113636 created and queued.
🤖 Automatically detected try build 1066537ce94b83c04b9e840838af0b66b0ef1500
🔍 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-113636 is now running

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

[craterbot]

🎉 Experiment pr-113636 is completed!
📊 6 regressed and 3 fixed (321870 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

[oli-obk]

All regressions are spurious disk failures

@bors r+

[bors]

📌 Commit d4fcef7df7b25f0d24b57531dc2289f4cfa2c23e has been approved by oli-obk

It is now in the queue for this repository.

[bors]

☔ The latest upstream changes (presumably #113328) made this pull request unmergeable. Please resolve the merge conflicts.

[cjgillot]

The previous check was only checking the def_id.
This would accept TAIT<T, U> being inferred to Tait<u32, u32>.
Do we want to accept that?

[oli-obk]

that is rejected later. I guess we could do some of these checks here, too, but I don't see any way we could miss doing the checks (as we get the hidden type from borrowck, not from typeck)

[oli-obk]

@bors r+

[bors]

📌 Commit 6875589 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 6875589 with merge f19439247f57f0c68e397536e9fb07b018599a72...

[bors]

💔 Test failed - checks-actions

[rust-log-analyzer]

The job dist-aarch64-linux failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[oli-obk]

@bors retry empty log

[bors]

⌛ Testing commit 6875589 with merge d351515...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing d351515 to master...

[rust-timer]

Finished benchmarking commit (d351515): 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

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)	-0.8%	[-1.0%, -0.7%]	2
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-0.8%	[-1.0%, -0.7%]	2

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: 660.475s -> 658.716s (-0.27%)