Port `#[cfg_attr]` to the new attribute parsing infrastructure #147532

JonathanBrouwer · 2025-10-09T15:41:30Z

This work in progress, not ready for review.
PR mostly for ci/perf runs

JonathanBrouwer · 2025-10-10T09:20:47Z

r? @jdonszelmann
Not ready for review yet, just assigning you

JonathanBrouwer · 2025-10-14T09:10:03Z

Port `#[cfg_attr]` to the new attribute parsing infrastructure

rust-bors · 2025-10-14T11:21:12Z

☀️ Try build successful (CI)
Build commit: ff502cb (ff502cb3140362d4d93bde4d537bcdb21bf639be, parent: 4b94758d2ba7d0ef71ccf5fde29ce4bc5d6fe2a4)

rust-timer · 2025-10-14T12:31:22Z

Finished benchmarking commit (ff502cb): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

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)	0.1%	[0.1%, 0.2%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.4%, -0.1%]	14
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -2.2%, secondary 0.9%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.1%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-2.2%	[-2.2%, -2.2%]	1
Improvements ✅ (secondary)	-1.3%	[-1.3%, -1.3%]	1
All ❌✅ (primary)	-2.2%	[-2.2%, -2.2%]	1

Cycles

Results (secondary 3.5%)

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

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

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 475.312s -> 475.298s (-0.00%)
Artifact size: 388.16 MiB -> 388.09 MiB (-0.02%)

rustbot · 2025-10-14T18:00:12Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

tests/ui/conditional-compilation/cfg_attr-attr-syntax-validation.stderr

JonathanBrouwer · 2025-10-14T18:02:12Z

@jdonszelmann I think the perf looks reasonable, more improvements than regressions and it's all secondary benchmarks anyways. Feel free to disagree and I can look into the regressions more though.
(I made no changes to the code since the perf run, only docs and tests, so no need to rerun)

compiler/rustc_attr_parsing/src/attributes/cfg.rs

compiler/rustc_attr_parsing/src/interface.rs

jdonszelmann · 2025-10-15T13:42:13Z

src/librustdoc/clean/cfg.rs

        for attr in doc_cfg {
            if let Some(cfg_mi) =
-                attr.meta_item().and_then(|attr| rustc_expand::config::parse_cfg(attr, sess))
+                attr.meta_item().and_then(|attr| rustc_expand::config::parse_cfg_old(attr, sess))


why are we still using the old infra in rustdoc?

This is for the cfg option in the #[doc] attribute

tests/ui/conditional-compilation/cfg_attr-attr-syntax-validation.stderr

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

rustbot · 2025-10-15T20:23:12Z

This PR was rebased onto a different master 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.

JonathanBrouwer · 2025-10-15T20:23:16Z

@jdonszelmann I think I improved the diagnostics a lot now :)
I am manually building the diagnostics because sadly I don't have access to the right context in parse_cfg_attr to make them using the normal methods on the context. It's all a little annoying because cfg_attr is special and we cannot use the new parser structs until we build a Parser object with the tokenstream of the attribute, but errors may already occur before that

@rustbot ready

JonathanBrouwer · 2025-10-15T21:03:06Z

tests/ui/rust-2018/removing-extern-crate-malformed-cfg.fixed

 //@ edition:2018
 //@ aux-build: remove-extern-crate.rs
 //@ run-rustfix
+//@ rustfix-only-machine-applicable


This is needed because otherwise it tries to apply the suggestion of the cfg_attr syntax which has holes and therefore fails

jdonszelmann · 2025-10-18T08:44:25Z

tests/ui/cfg/cfg-path-error.stderr

-   |                ^^^^^^^^
+   | ^^^^^^^^^^^^^^^--------^^^
+   | |              |
+   | |              expected a valid identifier here


could be cool if we could detect paths here, lets make an issue for that

jdonszelmann · 2025-10-18T08:45:22Z

@bors r+ rollup not entirely happy with this but it's a clear improvement

bors · 2025-10-18T08:45:25Z

📌 Commit 090dad0 has been approved by jdonszelmann

It is now in the queue for this repository.

Rollup of 6 pull requests Successful merges: - #146509 (Result/Option layout guarantee clarifications) - #147494 (std::thread spawn: Docs: Link to Builder::spawn; Make same.) - #147532 ( Port `#[cfg_attr]` to the new attribute parsing infrastructure) - #147783 (bootstrap: migrate to object 0.37) - #147792 (Fix autodiff incorrectly applying fat-lto to proc-macro crates ) - #147809 (rustdoc: Fix passes order so intra-doc links are collected after stripping passes) Failed merges: - #147813 (Warn on unused_attributes in uitests ) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #147532 - JonathanBrouwer:cfg_attr2, r=jdonszelmann Port `#[cfg_attr]` to the new attribute parsing infrastructure This work in progress, not ready for review. PR mostly for ci/perf runs

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JonathanBrouwer force-pushed the cfg_attr2 branch 2 times, most recently from 10cf134 to e9bdfb0 Compare October 10, 2025 08:44

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Auto merge of #147532 - JonathanBrouwer:cfg_attr2, r=<try>

ff502cb

Port `#[cfg_attr]` to the new attribute parsing infrastructure

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 14, 2025

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Oct 14, 2025

JonathanBrouwer marked this pull request as ready for review October 14, 2025 18:00

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JonathanBrouwer commented Oct 14, 2025

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JonathanBrouwer force-pushed the cfg_attr2 branch 2 times, most recently from 2d7c376 to 1a84725 Compare October 14, 2025 18:11

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JonathanBrouwer force-pushed the cfg_attr2 branch from 1a84725 to 48ca34d Compare October 14, 2025 18:52

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JonathanBrouwer force-pushed the cfg_attr2 branch from 48ca34d to 5e34be1 Compare October 14, 2025 19:07

jdonszelmann requested changes Oct 15, 2025

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JonathanBrouwer added 4 commits October 15, 2025 22:18

Rename some functions

52cc311

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

Move parse_cfg_attr to rustc_attr_parsing

e0c190f

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

Port #[cfg_attr] to the new attribute parsing infrastructure

7113d58

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

Changes in uitests for cfg_attr

090dad0

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

JonathanBrouwer force-pushed the cfg_attr2 branch from 5e34be1 to 090dad0 Compare October 15, 2025 20:23

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 Oct 15, 2025

JonathanBrouwer commented Oct 16, 2025

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jdonszelmann reviewed Oct 18, 2025

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bors 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 Oct 18, 2025

matthiaskrgr mentioned this pull request Oct 18, 2025

Rollup of 6 pull requests #147842

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bors merged commit 2b582ea into rust-lang:master Oct 18, 2025
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rustbot added this to the 1.92.0 milestone Oct 18, 2025

Port #[cfg_attr] to the new attribute parsing infrastructure #147532

Port #[cfg_attr] to the new attribute parsing infrastructure #147532

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Overall result: ❌✅ regressions and improvements - please read the text below

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Port `#[cfg_attr]` to the new attribute parsing infrastructure #147532

Port `#[cfg_attr]` to the new attribute parsing infrastructure #147532

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