Revert "Implement Debug for C-like enums with a concatenated string" by nnethercote · Pull Request #162164 · rust-lang/rust

nnethercote · 2026-09-02T01:14:43Z

From rust-lang#155452. Fixes rust-lang#162124.

rustbot · 2026-09-02T01:14:48Z

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rustbot · 2026-09-02T01:14:49Z

⚠️ Warning ⚠️

There are issue links (such as #123) in the commit messages of the following commits.
Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtree.
- f91c12f

clarfonthey · 2026-09-02T01:20:07Z

As mentioned in the libs meeting, I kind of consider the debug macros to be a weird edge case and mostly a libs thing even though they're part of the compiler, but I'm not going to bikeshed that particular issue in general.

That said, since major ecosystem breakage is mostly a non-starter for changes like this, I'm going to say it's okay for me to review this and give it my approval. We do probably still want this, but it's going to have to be done in a way that doesn't break existing crates, whether that's via an edition or some extra work on verifying the result of the macro evaluation.

r=me, pending the merge commit fix + CI passing.

r? clarfonthey

clarfonthey · 2026-09-02T15:21:56Z

@bors r+ rollup=iffy note="Revert major ecosystem (bitflags) regression, not perf, just fails to compile"

rust-bors · 2026-09-02T15:21:58Z

📌 Commit f91c12f has been approved by clarfonthey

It is now in the queue for this repository.

…=clarfonthey Revert "Implement Debug for C-like enums with a concatenated string" From rust-lang#155452. Fixes rust-lang#162124.

…uwer Rollup of 23 pull requests Successful merges: - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161847 (Preserve visibility in nested macro import suggestions) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162199 (docs(time): clarify exact seconds for hour and minute)

…=clarfonthey Revert "Implement Debug for C-like enums with a concatenated string" From rust-lang#155452. Fixes rust-lang#162124.

Rollup of 29 pull requests Successful merges: - #161694 (add `Complex` ABI run-make test) - #162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162132 (std: improve safety documentation in UNIX stack overflow code) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161847 (Preserve visibility in nested macro import suggestions) - #161951 (Windows: add fallback if `canonicalize` fails) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162180 (remove outdated next-solver FIXMEs) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162195 (docs(time): clarify exact seconds for week and day) - #162199 (docs(time): clarify exact seconds for hour and minute)

rustbot · 2026-09-03T10:28:45Z

beta backport approved as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle. Backport labels are handled by them.

…uwer Rollup of 25 pull requests Successful merges: - #161694 (add `Complex` ABI run-make test) - #162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162132 (std: improve safety documentation in UNIX stack overflow code) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161135 (Add `f16` and `f128` inline ASM support for PowerPC) - #161847 (Preserve visibility in nested macro import suggestions) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162111 (Update mailmap for Will Crichton and Petr Hosek) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm)

Rollup merge of #162164 - nnethercote:revert-concat-Debug, r=clarfonthey Revert "Implement Debug for C-like enums with a concatenated string" From #155452. Fixes #162124.

rust-timer · 2026-09-03T20:28:38Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (a056d7d): comparison URL.

Overall result: ❌ regressions - please read:

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.4%	[0.2%, 0.7%]	18
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 4.3%, secondary 2.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	4.3%	[4.3%, 4.3%]	1
Regressions ❌ (secondary)	2.2%	[0.8%, 3.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.3%	[4.3%, 4.3%]	1

Cycles

This perf run didn't have relevant results for this metric.

Binary size

Results (primary 0.4%, secondary -6.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.2%, 0.6%]	8
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.5%	[-12.1%, -0.9%]	12
All ❌✅ (primary)	0.4%	[0.2%, 0.6%]	8

Bootstrap: missing data
Artifact size: 401.86 MiB -> 403.42 MiB (0.39%)

nnethercote · 2026-09-03T20:46:39Z

The perf regression is expected: this PR is reverting a perf improvement that caused a correctness regression.

@rustbot label: +perf-regression-triaged

[beta] backports - Avoid arming the Windows TLS destructor guard in fibers #161451 - (partial) stdarch subtree update #161558 - Check to ensure we're running against the correct LLVM version #161788 - Make the LLVM version mismatch ICE a fatal error #162034 - Revert "Add `rustc_test_entrypoint_marker`" #161931 - Fix ICE of getting name from RPITIT #162071 - Update LLVM submodule #162133 - Revert "Implement Debug for C-like enums with a concatenated string" #162164 r? me

…uwer Rollup of 25 pull requests Successful merges: - rust-lang/rust#161694 (add `Complex` ABI run-make test) - rust-lang/rust#162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - rust-lang/rust#162164 (Revert "Implement Debug for C-like enums with a concatenated string") - rust-lang/rust#160564 (volatile: allow accesses to non-AM memory to trap) - rust-lang/rust#161579 (suggest calling a fn item used as the iterator of a `for` loop) - rust-lang/rust#162044 (coverage: Resolve spans to file-coordinates in a separate step) - rust-lang/rust#162120 (Introduce `PerOwnerLoweringState`) - rust-lang/rust#162132 (std: improve safety documentation in UNIX stack overflow code) - rust-lang/rust#162151 (Test itanium mangling of `f16` and `f128`) - rust-lang/rust#162162 (Don't special-case `!` in stability checks anymore) - rust-lang/rust#162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - rust-lang/rust#162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - rust-lang/rust#158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - rust-lang/rust#159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - rust-lang/rust#161135 (Add `f16` and `f128` inline ASM support for PowerPC) - rust-lang/rust#161847 (Preserve visibility in nested macro import suggestions) - rust-lang/rust#161972 (Improve tests for `#[track_caller]` in async) - rust-lang/rust#162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - rust-lang/rust#162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - rust-lang/rust#162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - rust-lang/rust#162111 (Update mailmap for Will Crichton and Petr Hosek) - rust-lang/rust#162152 (Revert "retrieve supported GCC targets from the sysroot") - rust-lang/rust#162153 (Prefer `LLVMGetVersion` for runtime info) - rust-lang/rust#162168 (fix ICE in project_goals/inherent) - rust-lang/rust#162171 (Explain LoongArch f16 NaN-boxing in inline asm)

[beta] backports - Avoid arming the Windows TLS destructor guard in fibers #161451 - (partial) stdarch subtree update #161558 - Check to ensure we're running against the correct LLVM version #161788 - Make the LLVM version mismatch ICE a fatal error #162034 - Revert "Add `rustc_test_entrypoint_marker`" #161931 - Fix ICE of getting name from RPITIT #162071 - Update LLVM submodule #162133 - Revert "Implement Debug for C-like enums with a concatenated string" #162164 r? me

Revert "Implement Debug for C-like enums with a concatenated string"

f91c12f

From rust-lang#155452. Fixes rust-lang#162124.

rustbot assigned davidtwco Sep 2, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 2, 2026

rustbot added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Sep 2, 2026

rustbot assigned clarfonthey and unassigned davidtwco Sep 2, 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 Sep 2, 2026

JonathanBrouwer mentioned this pull request Sep 2, 2026

Rollup of 23 pull requests #162206

Closed

JonathanBrouwer mentioned this pull request Sep 2, 2026

Rollup of 23 pull requests #162211

Closed

Zalathar mentioned this pull request Sep 3, 2026

Rollup of 29 pull requests #162221

Closed

rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Sep 3, 2026

JonathanBrouwer mentioned this pull request Sep 3, 2026

Rollup of 25 pull requests #162229

Merged

rust-bors Bot merged commit 82b1966 into rust-lang:main Sep 3, 2026
13 checks passed

rustbot added this to the 1.100.0 milestone Sep 3, 2026

cuviper mentioned this pull request Sep 3, 2026

[beta] backports #162258

Merged

cuviper modified the milestones: 1.100.0, 1.99.0 Sep 3, 2026

cuviper removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Sep 3, 2026

rustbot added the perf-regression Performance regression. label Sep 3, 2026

rustbot added the perf-regression-triaged The performance regression has been triaged. label Sep 3, 2026

nnethercote deleted the revert-concat-Debug branch September 3, 2026 20:46

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Revert "Implement Debug for C-like enums with a concatenated string" - #162164

Revert "Implement Debug for C-like enums with a concatenated string"#162164
rust-bors[bot] merged 1 commit into
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Overall result: ❌ regressions - please read:

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