Fix avoid cycle for self referential return type notation by amirHdev · Pull Request #159958 · rust-lang/rust

amirHdev · 2026-07-26T10:15:51Z

Fixes #159892 and #133613
we had to preserve and restore shadowed parameters in the impl trait overcapture lint and convert the resolved crash regression into a normal UI test which is applied to this patch

rustbot · 2026-07-26T13:15:05Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-07-26T13:15:07Z

r? @jieyouxu

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jieyouxu · 2026-07-29T04:55:16Z

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oli-obk

I understand the immediate-self-cycle solution in resolve_bound_vars, but not yet the entire picture here. I'm worried 133613 is only "fixed" accidentally and is now referencing the wrong bound vars, but thus not ICEing anymore

View changes since this review

oli-obk · 2026-07-29T11:17:00Z

+//@ dont-check-compiler-stderr
+//@ dont-require-annotations: ERROR
+
+struct Wrapper<'a>();


why was this unrelated type ever part of the logic that caused the ICE?

one thing to try is to add more lifetime params here until they are more than the anonymous ones on the function, maybe then the ICE reoccurs?

Wrapper is only there to force error recovery. it is a separate HIR owner and is not the source of the bound variable list used for IntFactory::stream
I increased it to four unrelated lifetime parameters as you suggested. on the this patch base commit the compiler still panics with
Not enough bound vars: ... IntFactory::stream ... not found in []
and exits with status 101
With the patch applied the exact same test only reports the four expected E0392 diagnostics. this shows that the fix is addressing the underlying problem

Ok I see now. the query cycle happens during fn_sig, which, when part of a cycle returns a dummy value instead of causing a fatal error. Thus the entire output of resolve_bound_vars query is now bogus, as invoking it again will not cause a cycle now, but use the dummy value from the cached failed fn_sig query. This produces an empty list of bound vars.

Your fix avoids the cycle entirely and everything is good.

rustbot · 2026-07-29T11:19:51Z

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

amirHdev · 2026-07-29T16:54:00Z

@rustbot ready

oli-obk · 2026-07-30T16:03:57Z

@bors squash avoid cycle for self referential return type notation

rust-bors · 2026-07-30T16:04:01Z

Unknown argument "avoid". Did you mean to use @bors squash [msg|message="<commit-msg>"|description]? Run @bors help or go to https://bors.rust-lang.org/help to see available commands.

oli-obk · 2026-07-30T16:04:17Z

@bors squash msg="avoid cycle for self referential return type notation"

rust-bors · 2026-07-30T16:04:49Z

🔨 2 commits were squashed into af64640.

oli-obk · 2026-07-30T16:39:59Z

@bors r+ rollup

rust-bors · 2026-07-30T16:40:02Z

📌 Commit af64640 has been approved by oli-obk

It is now in the queue for this repository.

…uwer Rollup of 25 pull requests Successful merges: - #160204 (Sync from portable simd 2026 07 30) - #138230 (Add `raw_borrows_via_references` lint) - #158057 (Don't escape U+FF9E and U+FF9F in `escape_debug_ext`) - #160015 (refactor(mir-transform): Merge `can_be_overridden`, `is_required` and `is_enabled` into one) - #160031 (std: make positioned I/O unsupported on VxWorks) - #160125 (Fix typing mode handling in transmute checks and rustc_dump_layout) - #160152 (Create on-demand CI job for testing EC2 instances) - #160232 (rustdoc: fix ICE when a grapheme cluster joins a Prepend-class character to `_` or `:`) - #159214 (std: improve the documentation of the random feature) - #159818 (Resolve vars before calling `unnormalized_obligations`) - #159955 (Stop using higher-order macros to declare arenas) - #159958 (Fix avoid cycle for self referential return type notation) - #160040 (Split function parsing out of `item.rs` to a new module.) - #160044 (Add regression tests for fixed dead-code issues) - #160144 (renovate: group lockfiles PRs) - #160149 (Fix Windows on Arm PAC default) - #160164 (Derive `GenericTypeVisitable` for `RegionConstraint`) - #160175 (Try to recover less from incorrectly parsed const arg) - #160177 (A few more "predicate"-to-"clause" renamings) - #160181 (Mark `Tuple` and `FnPtr` traits `#[fundamental]`) - #160192 (Fix ICE for parsing issue with a closing brace) - #160209 (bootstrap: Remove method `Subcommand::kind`) - #160221 (Remove `Copy` supertrait from `VaList`) - #160223 (interpret: rename validate_operand → validate_place) - #160234 (Always use short ty path for call with missing arguments suggestion)

Rollup merge of #159958 - amirHdev:fix-rtn-cycle, r=oli-obk Fix avoid cycle for self referential return type notation Fixes #159892 and #133613 we had to preserve and restore shadowed parameters in the impl trait overcapture lint and convert the resolved crash regression into a normal UI test which is applied to this patch

…uwer Rollup of 25 pull requests Successful merges: - rust-lang/rust#160204 (Sync from portable simd 2026 07 30) - rust-lang/rust#138230 (Add `raw_borrows_via_references` lint) - rust-lang/rust#158057 (Don't escape U+FF9E and U+FF9F in `escape_debug_ext`) - rust-lang/rust#160015 (refactor(mir-transform): Merge `can_be_overridden`, `is_required` and `is_enabled` into one) - rust-lang/rust#160031 (std: make positioned I/O unsupported on VxWorks) - rust-lang/rust#160125 (Fix typing mode handling in transmute checks and rustc_dump_layout) - rust-lang/rust#160152 (Create on-demand CI job for testing EC2 instances) - rust-lang/rust#160232 (rustdoc: fix ICE when a grapheme cluster joins a Prepend-class character to `_` or `:`) - rust-lang/rust#159214 (std: improve the documentation of the random feature) - rust-lang/rust#159818 (Resolve vars before calling `unnormalized_obligations`) - rust-lang/rust#159955 (Stop using higher-order macros to declare arenas) - rust-lang/rust#159958 (Fix avoid cycle for self referential return type notation) - rust-lang/rust#160040 (Split function parsing out of `item.rs` to a new module.) - rust-lang/rust#160044 (Add regression tests for fixed dead-code issues) - rust-lang/rust#160144 (renovate: group lockfiles PRs) - rust-lang/rust#160149 (Fix Windows on Arm PAC default) - rust-lang/rust#160164 (Derive `GenericTypeVisitable` for `RegionConstraint`) - rust-lang/rust#160175 (Try to recover less from incorrectly parsed const arg) - rust-lang/rust#160177 (A few more "predicate"-to-"clause" renamings) - rust-lang/rust#160181 (Mark `Tuple` and `FnPtr` traits `#[fundamental]`) - rust-lang/rust#160192 (Fix ICE for parsing issue with a closing brace) - rust-lang/rust#160209 (bootstrap: Remove method `Subcommand::kind`) - rust-lang/rust#160221 (Remove `Copy` supertrait from `VaList`) - rust-lang/rust#160223 (interpret: rename validate_operand → validate_place) - rust-lang/rust#160234 (Always use short ty path for call with missing arguments suggestion)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 26, 2026

amirHdev force-pushed the fix-rtn-cycle branch 2 times, most recently from 037d040 to 6e1755a Compare July 26, 2026 12:10

amirHdev marked this pull request as ready for review July 26, 2026 13:15

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 26, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 26, 2026

rustbot assigned jieyouxu Jul 26, 2026

rustbot added the T-types Relevant to the types team, which will review and decide on the PR/issue. label Jul 29, 2026

rustbot assigned oli-obk and unassigned jieyouxu Jul 29, 2026

oli-obk reviewed Jul 29, 2026

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Comment thread tests/ui/associated-type-bounds/return-type-notation/nested-rtn-error-recovery-issue-133613.rs Outdated

oli-obk requested changes Jul 29, 2026

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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-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 29, 2026

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 Jul 29, 2026

amirHdev requested a review from oli-obk July 29, 2026 17:09

oli-obk mentioned this pull request Jul 30, 2026

Next steps for FnDef binder changes (instantiate most FnDef binders) #159403

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avoid cycle for self referential return type notation

af64640

rust-bors Bot force-pushed the fix-rtn-cycle branch from f4caf4f to af64640 Compare July 30, 2026 16:04

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 Jul 30, 2026

JonathanBrouwer mentioned this pull request Jul 30, 2026

Rollup of 25 pull requests #160238

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rust-bors Bot merged commit 8384a31 into rust-lang:main Jul 31, 2026
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rustbot added this to the 1.99.0 milestone Jul 31, 2026

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