Detect cycle errors hidden by opaques during monomorphization #115801

compiler-errors · 2023-09-12T20:02:52Z

Opaque types may reveal to projections, which themselves normalize to opaques. We don't currently normalize when checking that opaques are cyclical, and we may also not know that the opaque is cyclical until monomorphization (see tests/ui/type-alias-impl-trait/mututally-recursive-overflow.rs).

Detect cycle errors in normalize_projection_ty and report a fatal overflow (in the old solver). Luckily, this is already detected as a fatal overflow in the new solver.

Fixes #112047

rustbot · 2023-09-12T20:03:02Z

r? @davidtwco

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compiler-errors · 2023-09-12T21:38:37Z

🤦

@rustbot author

compiler-errors · 2023-09-18T22:04:11Z

@rustbot ready

This rustdoc-only hack makes me sad, but it does fix a strange TAIT/RPITIT-only post-mono error in a more graceful way than ICEing. Maybe @oli-obk can leave some thoughts too.

oli-obk · 2023-09-19T11:41:40Z

compiler/rustc_traits/src/normalize_projection_ty.rs

+                    // Rustdoc may attempt to normalize type alias types which are not
+                    // well-formed. Rustdoc also normalizes types that are just not
+                    // well-formed, since we don't do as much HIR analysis (checking
+                    // that impl vars are constrained by the signature, for example).


Does it do that for code that passes rustc? We are allowed to cause new errors in rustdoc if the code also wouldn't compile in rustc.

a more graceful way than ICEing

ah, that's the issue. hmm.. does rustdoc unwrap something instead of reporting an error? or where is the ICE coming from?

We are allowed to cause new errors in rustdoc if the code also wouldn't compile in rustc

Well, the problem is that we need to do HIR analysis to make sure we don't have things like malformed and overlapping impl blocks too. These are probably not what we want to "fix" in rustdoc, since we compile rustdoc with all features enabled and stuff?

We also would need to check all type aliases as well-formed too, which we don't even do in rustc yet.

does rustdoc unwrap something instead of reporting an error? or where is the ICE coming from?

The ICE is coming from a failed projection in the QueryNormalizer.

What happens is that we hit a cycle here:

rust/compiler/rustc_trait_selection/src/traits/project.rs

Lines 1193 to 1196 in 0692db1

Err(ProjectionCacheEntry::Recur) => {

debug!("recur cache");

return Err(InProgress);

}

Which means we treat the projection as ambiguous and emit a projection goal with an infer var on the RHS. That causes us to hit this assertion with debug assertions enabled:

rust/compiler/rustc_traits/src/normalize_erasing_regions.rs

Line 50 in 0692db1

debug_assert!(!erased.has_infer(), "{erased:?}");

Or just errors out with NoSolution, which causes normalize_erasing_regions to ICE.

Ah... yea that makes sense sadly.

Tho Rustdoc is moving towards doing wf checks in the future, so this will get cleaned up

oli-obk · 2023-09-19T16:56:38Z

@bors r+

bors · 2023-09-19T16:56:40Z

📌 Commit 8fbd78c has been approved by oli-obk

It is now in the queue for this repository.

…llaumeGomez Rollup of 6 pull requests Successful merges: - rust-lang#113383 (style-guide: Add section on bugs, and resolving bugs) - rust-lang#115499 (rustc_target/riscv: Fix passing of transparent unions with only one non-ZST member) - rust-lang#115801 (Detect cycle errors hidden by opaques during monomorphization) - rust-lang#115947 (Custom code classes in docs warning) - rust-lang#115957 (fix mismatched symbols) - rust-lang#115958 (explain mysterious addition in float minimum/maximum) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#115801 - compiler-errors:async-cycle-mono, r=oli-obk Detect cycle errors hidden by opaques during monomorphization Opaque types may reveal to projections, which themselves normalize to opaques. We don't currently normalize when checking that opaques are cyclical, and we may also not know that the opaque is cyclical until monomorphization (see `tests/ui/type-alias-impl-trait/mututally-recursive-overflow.rs`). Detect cycle errors in `normalize_projection_ty` and report a fatal overflow (in the old solver). Luckily, this is already detected as a fatal overflow in the new solver. Fixes rust-lang#112047

rustbot assigned davidtwco Sep 12, 2023

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rust-cloud-vms bot force-pushed the async-cycle-mono branch from 75d4bc0 to 704ded3 Compare September 13, 2023 17:33

Detect cycle errors hidden by opaques during monomorphization

8fbd78c

rust-cloud-vms bot force-pushed the async-cycle-mono branch from 704ded3 to 8fbd78c Compare September 13, 2023 17:35

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 18, 2023

oli-obk reviewed Sep 19, 2023

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GuillaumeGomez mentioned this pull request Sep 19, 2023

Rollup of 6 pull requests #115979

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bors merged commit 0060db7 into rust-lang:master Sep 19, 2023
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StackOverflowExcept1on mentioned this pull request Oct 26, 2023

regression when compiling substrate node with -Cinstrument-coverage #117211

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StackOverflowExcept1on mentioned this pull request Dec 6, 2023

EquivocationReportSystem trait bounds can recursively use T::KeyOwnerProof in some cases paritytech/polkadot-sdk#2641

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Detect cycle errors hidden by opaques during monomorphization #115801

Detect cycle errors hidden by opaques during monomorphization #115801

compiler-errors commented Sep 12, 2023

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bors commented Sep 19, 2023

	Err(ProjectionCacheEntry::Recur) => {
	debug!("recur cache");
	return Err(InProgress);
	}

Detect cycle errors hidden by opaques during monomorphization #115801

Detect cycle errors hidden by opaques during monomorphization #115801

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