Add more robust handling of nested query cycles by Zoxc · Pull Request #154389 · rust-lang/rust

Zoxc · 2026-03-25T22:29:47Z

This adds more robust handling of query cycle that occur while we are already printing a query cycle error. Such nested query cycle are compiler bugs and this adds special handling so that both the nested query cycle and the outer query cycle are printed. Doubly nested query cycle errors are ignored to prevent infinite recursion.

Zoxc · 2026-03-25T22:32:44Z

The nested query cycles are currently printed as errors as I don't think we have the mechanism to resume after emitting a bug.

This means we have 2 tests that are failing which were previously "undetected".

petrochenkov · 2026-04-07T11:13:27Z

This is now a blocker for the delegation work (like #154368) where you get compiler hangs instead of query cycle errors quite often due to this issue.
I'm going to review and merge this sooner rather than later to address the hangs, even if the implementation is not perfect, and @Zalathar and @nnethercote can cleanup it later if necessary.

zetanumbers · 2026-04-07T11:22:35Z

We shouldn't be testing for ICEs, but fixing them instead.

"internal compiler error" is just a part of the message, I'm not sure if it's actually a compiler bug, and whether it's possible to eliminate it in all cases, if query cycles in general are not avoidable.

Zoxc · 2026-04-07T11:30:51Z

This is currently racy as we can resume multiple query cycles at once, so the global counter doesn't work. I have a branch which changes that, but I was waiting for #154146 to land first.

petrochenkov · 2026-04-07T13:10:39Z

Blocked on #153999 and #154146.
@rustbot blocked

Zoxc · 2026-04-07T23:47:21Z

Blocked on #154973

petrochenkov · 2026-04-12T12:31:31Z

#154973 has landed.
@rustbot author

rustbot · 2026-04-12T12:31:37Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

rustbot · 2026-04-12T13:56:54Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

petrochenkov · 2026-04-13T10:14:32Z

(Please, mark with the label if/when this is ready.)

Zoxc · 2026-04-13T14:35:17Z

I'd say this is good enough to help out with the OOM cases now.

@rustbot ready

petrochenkov · 2026-04-13T15:25:18Z

@bors r+

rust-bors · 2026-04-13T15:25:22Z

📌 Commit 6442b48 has been approved by petrochenkov

It is now in the queue for this repository.

Add more robust handling of nested query cycles This adds more robust handling of query cycle that occur while we are already printing a query cycle error. Such nested query cycle are compiler bugs and this adds special handling so that both the nested query cycle and the outer query cycle are printed. Doubly nested query cycle errors are ignored to prevent infinite recursion.

…uwer Rollup of 19 pull requests Successful merges: - #155162 (relnotes for 1.95) - #140763 (Change codegen of LLVM intrinsics to be name-based, and add llvm linkage support for `bf16(xN)` and `i1xN`) - #153604 (Fix thread::available_parallelism on WASI targets with threads) - #154193 (Implement EII for statics) - #154389 (Add more robust handling of nested query cycles) - #154435 (resolve: Some import resolution cleanups) - #155236 (Normalize individual predicate of `InstantiatedPredicates` inside `predicates_for_generics`) - #155243 (cg_ssa: transmute between scalable vectors) - #153941 (tests/debuginfo/basic-stepping.rs: Explain why all lines are not steppable) - #154587 (Add --verbose-run-make-subprocess-output flag to suppress verbose run-make output for passing tests) - #154624 (Make `DerefPure` dyn-incompatible) - #154929 (Add `const Default` impls for `LazyCell` and `LazyLock`) - #154944 (Small refactor of `arena_cache` query values) - #155055 (UI automation) - #155062 (Move tests from `tests/ui/issues/` to appropriate directories) - #155131 (Stabilize feature `uint_bit_width`) - #155147 (Stabilize feature `int_lowest_highest_one`) - #155174 (Improve emission of `UnknownDiagnosticAttribute` lint) - #155194 (Fix manpage version replacement and use verbose version)

Rollup merge of #154389 - Zoxc:nested-cycles, r=petrochenkov Add more robust handling of nested query cycles This adds more robust handling of query cycle that occur while we are already printing a query cycle error. Such nested query cycle are compiler bugs and this adds special handling so that both the nested query cycle and the outer query cycle are printed. Doubly nested query cycle errors are ignored to prevent infinite recursion.

…uwer Rollup of 19 pull requests Successful merges: - rust-lang/rust#155162 (relnotes for 1.95) - rust-lang/rust#140763 (Change codegen of LLVM intrinsics to be name-based, and add llvm linkage support for `bf16(xN)` and `i1xN`) - rust-lang/rust#153604 (Fix thread::available_parallelism on WASI targets with threads) - rust-lang/rust#154193 (Implement EII for statics) - rust-lang/rust#154389 (Add more robust handling of nested query cycles) - rust-lang/rust#154435 (resolve: Some import resolution cleanups) - rust-lang/rust#155236 (Normalize individual predicate of `InstantiatedPredicates` inside `predicates_for_generics`) - rust-lang/rust#155243 (cg_ssa: transmute between scalable vectors) - rust-lang/rust#153941 (tests/debuginfo/basic-stepping.rs: Explain why all lines are not steppable) - rust-lang/rust#154587 (Add --verbose-run-make-subprocess-output flag to suppress verbose run-make output for passing tests) - rust-lang/rust#154624 (Make `DerefPure` dyn-incompatible) - rust-lang/rust#154929 (Add `const Default` impls for `LazyCell` and `LazyLock`) - rust-lang/rust#154944 (Small refactor of `arena_cache` query values) - rust-lang/rust#155055 (UI automation) - rust-lang/rust#155062 (Move tests from `tests/ui/issues/` to appropriate directories) - rust-lang/rust#155131 (Stabilize feature `uint_bit_width`) - rust-lang/rust#155147 (Stabilize feature `int_lowest_highest_one`) - rust-lang/rust#155174 (Improve emission of `UnknownDiagnosticAttribute` lint) - rust-lang/rust#155194 (Fix manpage version replacement and use verbose version)

matthiaskrgr · 2026-04-14T21:03:09Z

+}
+
+#[derive(Diagnostic)]
+#[diag("internal compiler error: query cycle when printing cycle detected")]


this is very confusing as there is neither a stacktrace nor a an according exit code, why not just make this a bug!() ?

View changes since the review

Because we need to continue execution to print the outermost query cycle. I'm not sure if it's overkill to add a new diagnostic mode for that.

Overkill, IMO, I'd rather just remove "internal compiler error" from the message #154389 (comment).

They're always internal compiler errors though, so that wouldn't be great.

…uwer Rollup of 19 pull requests Successful merges: - rust-lang/rust#155162 (relnotes for 1.95) - rust-lang/rust#140763 (Change codegen of LLVM intrinsics to be name-based, and add llvm linkage support for `bf16(xN)` and `i1xN`) - rust-lang/rust#153604 (Fix thread::available_parallelism on WASI targets with threads) - rust-lang/rust#154193 (Implement EII for statics) - rust-lang/rust#154389 (Add more robust handling of nested query cycles) - rust-lang/rust#154435 (resolve: Some import resolution cleanups) - rust-lang/rust#155236 (Normalize individual predicate of `InstantiatedPredicates` inside `predicates_for_generics`) - rust-lang/rust#155243 (cg_ssa: transmute between scalable vectors) - rust-lang/rust#153941 (tests/debuginfo/basic-stepping.rs: Explain why all lines are not steppable) - rust-lang/rust#154587 (Add --verbose-run-make-subprocess-output flag to suppress verbose run-make output for passing tests) - rust-lang/rust#154624 (Make `DerefPure` dyn-incompatible) - rust-lang/rust#154929 (Add `const Default` impls for `LazyCell` and `LazyLock`) - rust-lang/rust#154944 (Small refactor of `arena_cache` query values) - rust-lang/rust#155055 (UI automation) - rust-lang/rust#155062 (Move tests from `tests/ui/issues/` to appropriate directories) - rust-lang/rust#155131 (Stabilize feature `uint_bit_width`) - rust-lang/rust#155147 (Stabilize feature `int_lowest_highest_one`) - rust-lang/rust#155174 (Improve emission of `UnknownDiagnosticAttribute` lint) - rust-lang/rust#155194 (Fix manpage version replacement and use verbose version)

Zoxc mentioned this pull request Mar 25, 2026

Improved handling for cycles within the query system itself #154387

Open

petrochenkov mentioned this pull request Mar 26, 2026

delegation: fix cycles during delayed lowering #154368

Merged

Zoxc force-pushed the nested-cycles branch from a651775 to 0b862fa Compare March 30, 2026 07:18

petrochenkov self-assigned this Apr 7, 2026

petrochenkov removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Apr 7, 2026

petrochenkov marked this pull request as ready for review April 7, 2026 11:09

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 7, 2026

zetanumbers reviewed Apr 7, 2026

View reviewed changes

Comment thread tests/ui/query-system/query-cycle-printing-issue-151358.stderr

zetanumbers reviewed Apr 7, 2026

View reviewed changes

Comment thread tests/ui/parallel-rustc/default-trait-shadow-cycle-issue-151358.stderr

zetanumbers reviewed Apr 7, 2026

View reviewed changes

Comment thread compiler/rustc_query_impl/src/execution.rs

petrochenkov mentioned this pull request Apr 7, 2026

Remove TaggedQueryKey::def_kind #153999

Merged

rustbot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 7, 2026

This comment has been minimized.

Sign in to view

aerooneqq mentioned this pull request Apr 10, 2026

delegation: OOM #155060

Open

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Apr 12, 2026

Add more robust handling of nested query cycles

6442b48

Zoxc force-pushed the nested-cycles branch from 0b862fa to 6442b48 Compare April 12, 2026 13:56

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 Apr 13, 2026

rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 13, 2026

This was referenced Apr 13, 2026

Rollup of 20 pull requests #155245

Closed

Rollup of 19 pull requests #155253

Merged

rust-bors bot merged commit e39dfc5 into rust-lang:main Apr 13, 2026
11 checks passed

rustbot added this to the 1.97.0 milestone Apr 13, 2026

Zoxc deleted the nested-cycles branch April 14, 2026 00:53

matthiaskrgr reviewed Apr 14, 2026

View reviewed changes

Uh oh!

Conversation

Zoxc commented Mar 25, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Zoxc commented Mar 25, 2026

Uh oh!

petrochenkov commented Apr 7, 2026

Uh oh!

zetanumbers Apr 7, 2026

Choose a reason for hiding this comment

Uh oh!

petrochenkov Apr 13, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Zoxc commented Apr 7, 2026

Uh oh!

Uh oh!

petrochenkov commented Apr 7, 2026

Uh oh!

This comment has been minimized.

Zoxc commented Apr 7, 2026

Uh oh!

petrochenkov commented Apr 12, 2026

Uh oh!

rustbot commented Apr 12, 2026

Uh oh!

rustbot commented Apr 12, 2026

Uh oh!

petrochenkov commented Apr 13, 2026

Uh oh!

Zoxc commented Apr 13, 2026

Uh oh!

petrochenkov commented Apr 13, 2026

Uh oh!

rust-bors bot commented Apr 13, 2026

Uh oh!

Uh oh!

matthiaskrgr Apr 14, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Zoxc Apr 14, 2026

Choose a reason for hiding this comment

Uh oh!

petrochenkov Apr 15, 2026

Choose a reason for hiding this comment

Uh oh!

Zoxc Apr 15, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

Zoxc commented Mar 25, 2026 •

edited

Loading

matthiaskrgr Apr 14, 2026 •

edited by rustbot

Loading