Skip to content

regression: "cycle detected when borrow-checking" in offset_of! #150464

New issue
New issue
Closed
#150557
Closed
regression: "cycle detected when borrow-checking" in offset_of!#150464
#150557
Assignees
dianne
Labels
A-arrayArea: `[T; N]`A-const-evalArea: Constant evaluation, covers all const contexts (static, const fn, ...)A-constant-promotionArea: constant promotionC-bugCategory: This is a bug.I-cycleIssue: A query cycle occurred while none was expectedP-mediumMedium priorityS-has-bisectionStatus: A bisection has been found for this issueS-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issueT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.T-langRelevant to the language teamWG-const-evalWorking group: Const evaluationregression-from-stable-to-betaPerformance or correctness regression from stable to beta.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.
Milestone
1.93.0

Description

@cuviper
cuviper
opened on Dec 28, 2025
[INFO] [stdout] error[E0391]: cycle detected when borrow-checking `firmware::operation::implement::stm::gain::tests::test_phase_half`
[INFO] [stdout]    --> src/firmware/operation/implement/stm/gain.rs:649:5
[INFO] [stdout]     |
[INFO] [stdout] 649 |     fn test_phase_half() {
[INFO] [stdout]     |     ^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout] note: ...which requires promoting constants in MIR for `firmware::operation::implement::stm::gain::tests::test_phase_half`...
[INFO] [stdout]    --> src/firmware/operation/implement/stm/gain.rs:649:5
[INFO] [stdout]     |
[INFO] [stdout] 649 |     fn test_phase_half() {
[INFO] [stdout]     |     ^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] note: ...which requires simplifying constant for the type system `firmware::operation::implement::stm::gain::tests::test_phase_half::{constant#0}`...
[INFO] [stdout]    --> src/firmware/operation/implement/stm/gain.rs:704:20
[INFO] [stdout]     |
[INFO] [stdout] 704 |                 tx[offset_of!(GainSTMHead, flag)] & 0x3F
[INFO] [stdout]     |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] note: ...which requires const-evaluating + checking `firmware::operation::implement::stm::gain::tests::test_phase_half::{constant#0}`...
[INFO] [stdout]    --> src/firmware/operation/implement/stm/gain.rs:704:20
[INFO] [stdout]     |
[INFO] [stdout] 704 |                 tx[offset_of!(GainSTMHead, flag)] & 0x3F
[INFO] [stdout]     |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] note: ...which requires caching mir of `firmware::operation::implement::stm::gain::tests::test_phase_half::{constant#0}` for CTFE...
[INFO] [stdout]    --> src/firmware/operation/implement/stm/gain.rs:704:20
[INFO] [stdout]     |
[INFO] [stdout] 704 |                 tx[offset_of!(GainSTMHead, flag)] & 0x3F
[INFO] [stdout]     |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] note: ...which requires elaborating drops for `firmware::operation::implement::stm::gain::tests::test_phase_half::{constant#0}`...
[INFO] [stdout]    --> src/firmware/operation/implement/stm/gain.rs:704:20
[INFO] [stdout]     |
[INFO] [stdout] 704 |                 tx[offset_of!(GainSTMHead, flag)] & 0x3F
[INFO] [stdout]     |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]     = note: ...which again requires borrow-checking `firmware::operation::implement::stm::gain::tests::test_phase_half`, completing the cycle
[INFO] [stdout]     = note: cycle used when running analysis passes on crate `autd3_driver`
[INFO] [stdout]     = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
[INFO] [stdout]     = note: this error originates in the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info)

https://crater-reports.s3.amazonaws.com/beta-1.93-3/beta-2025-12-09/reg/autd3-driver-38.0.1/log.txt

@rustbot modify labels: +regression-from-stable-to-beta -regression-untriaged

Activity

  1. cuviper
    added a parent issue on Dec 28, 2025
  2. cuviper
    added
    C-bugCategory: This is a bug.
    regression-untriagedUntriaged performance or correctness regression.
    on Dec 28, 2025
  3. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    regression-from-stable-to-betaPerformance or correctness regression from stable to beta.
    and removed
    regression-untriagedUntriaged performance or correctness regression.
    on Dec 28, 2025
  4. cuviper
    added this to the 1.93.0 milestone on Dec 28, 2025
  5. fmease
    added
    I-cycleIssue: A query cycle occurred while none was expected
    E-needs-bisectionCall for participation: This issue needs bisection: https://github.com/rust-lang/cargo-bisect-rustc
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    E-needs-mcveCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example
    T-typesRelevant to the types team, which will review and decide on the PR/issue.
    and removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Dec 28, 2025

  6. theemathas commented on Dec 29, 2025

    @theemathas
    theemathas
    on Dec 29, 2025
    Contributor

    MCVE:

    use std::mem::offset_of;

struct Thing(i32);

pub fn foo() {
    let temp = [0u8];
    let _ = &(temp[offset_of!(Thing, 0)] & 0u8);
}
    Error output 
    error[E0391]: cycle detected when borrow-checking `foo`
 --> src/lib.rs:5:1
  |
5 | pub fn foo() {
  | ^^^^^^^^^^^^
  |
note: ...which requires promoting constants in MIR for `foo`...
 --> src/lib.rs:5:1
  |
5 | pub fn foo() {
  | ^^^^^^^^^^^^
note: ...which requires simplifying constant for the type system `foo::{constant#0}`...
 --> src/lib.rs:7:20
  |
7 |     let _ = &(temp[offset_of!(Thing, 0)] & 0u8);
  |                    ^^^^^^^^^^^^^^^^^^^^
note: ...which requires const-evaluating + checking `foo::{constant#0}`...
 --> src/lib.rs:7:20
  |
7 |     let _ = &(temp[offset_of!(Thing, 0)] & 0u8);
  |                    ^^^^^^^^^^^^^^^^^^^^
note: ...which requires caching mir of `foo::{constant#0}` for CTFE...
 --> src/lib.rs:7:20
  |
7 |     let _ = &(temp[offset_of!(Thing, 0)] & 0u8);
  |                    ^^^^^^^^^^^^^^^^^^^^
note: ...which requires elaborating drops for `foo::{constant#0}`...
 --> src/lib.rs:7:20
  |
7 |     let _ = &(temp[offset_of!(Thing, 0)] & 0u8);
  |                    ^^^^^^^^^^^^^^^^^^^^
  = note: ...which again requires borrow-checking `foo`, completing the cycle
  = note: cycle used when running analysis passes on crate `playground`
  = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
  = note: this error originates in the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0391`.

  7. 18 remaining items

  8. lcnr commented on Dec 30, 2025

    @lcnr
    lcnr
    on Dec 30, 2025
    Contributor

    I think we should stop trying to evaluate const blocks here, they are guaranteed to query cycle 😁

  9. dianne
    self-assigned this
    on Dec 31, 2025

  10. apiraino commented on Jan 22, 2026

    @apiraino
    apiraino
    on Jan 22, 2026
    Contributor

    Assigning priority (discussion on Zulip).

    @rustbot label -I-prioritize +P-medium

  11. rustbot
    added
    P-mediumMedium priority
    and removed
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Jan 22, 2026
  12. JonathanBrouwer
    added a commit that references this issue on Jan 27, 2026

    Rollup merge of rust-lang#150557 - dianne:no-const-block-eval-in-prom…

    53fb684
  13. rust-bors
    closed this as completedin 53fb684on Jan 27, 2026
  14. rust-timer
    added a commit that references this issue on Jan 27, 2026

    Unrolled build for #150557

    8d0fe88
  15. github-actions
    added 3 commits that reference this issue on Jan 28, 2026

    Rollup merge of #150557 - dianne:no-const-block-eval-in-promotion, r=…

    e24093f

    Rollup merge of #150557 - dianne:no-const-block-eval-in-promotion, r=…

    5ce2dfd

    Rollup merge of #150557 - dianne:no-const-block-eval-in-promotion, r=…

    340ebff
  16. s5suzuki
    added 3 commits that reference this issue on Feb 9, 2026

    disable `test_phase_half` test due to regression introduced in Rust 1…

    48d18fb

    disable `test_phase_half` test due to regression introduced in Rust 1…

    8487017

    disable `test_phase_half` test due to regression introduced in Rust 1…

    fd21973
  17. ghaaj
    added a commit that references this issue on Aug 7, 2026

    Rollup merge of #150557 - dianne:no-const-block-eval-in-promotion, r=…

    ca95a93
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

Labels

A-arrayArea: `[T; N]`A-const-evalArea: Constant evaluation, covers all const contexts (static, const fn, ...)A-constant-promotionArea: constant promotionC-bugCategory: This is a bug.I-cycleIssue: A query cycle occurred while none was expectedP-mediumMedium priorityS-has-bisectionStatus: A bisection has been found for this issueS-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issueT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.T-langRelevant to the language teamWG-const-evalWorking group: Const evaluationregression-from-stable-to-betaPerformance or correctness regression from stable to beta.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.

Type

No type

Projects

No projects

    Milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions