Encode cfg trace, not its early counterpart to fix cross-crate doc(auto_cfg)

[fmease]

Fixes #141301.

Rambling about target_feature which I didn't touch here

Regarding #141301 (comment) (#[target_feature(enable = …)] on inlined cross-crate re-exports), it has the same underlying cause (namely, we neither encode target_feature nor AttributeKind::TargetFeature in the crate metadata). However, I didn't make that change because I first want to experiment with querying TyCtxt::codegen_fn_attrs in rustdoc instead which already works cross-crate (and also use to it for reconstructing no_mangle, export_name, link_section to avoid encoding these attributes unnecessarily (basically reverting #144050) as suggested in #144004 (comment)).

r? GuillaumeGomez

[GuillaumeGomez]

Great, thanks! r=me once CI pass.

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

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spellchecking files
building external tool typos from package typos-cli@1.38.1
finished building tool typos
npm WARN deprecated puppeteer@22.15.0: < 24.10.2 is no longer supported
npm ERR! code 127
npm ERR! git dep preparation failed
npm ERR! command /node/bin/node /node/lib/node_modules/npm/bin/npm-cli.js install --force --cache=/home/user/.npm --prefer-offline=false --prefer-online=false --offline=false --no-progress --no-save --no-audit --include=dev --include=peer --include=optional --no-package-lock-only --no-dry-run
npm ERR! npm WARN using --force Recommended protections disabled.
npm ERR! npm WARN deprecated inflight@1.0.6: This module is not supported, and leaks memory. Do not use it. Check out lru-cache if you want a good and tested way to coalesce async requests by a key value, which is much more comprehensive and powerful.
npm ERR! npm WARN deprecated glob@7.2.3: Glob versions prior to v9 are no longer supported
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npm ERR! npm WARN deprecated read-package-json@2.1.2: This package is no longer supported. Please use @npmcli/package-json instead.
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npm ERR! npm ERR! code 127
npm ERR! npm ERR! path /home/user/.npm/_cacache/tmp/git-cloneXXXXXXPTKYas/node_modules/rollup
npm ERR! npm ERR! command failed
npm ERR! npm ERR! command sh -c patch-package
npm ERR! npm ERR! sh: 1: patch-package: not found
npm ERR! 
npm ERR! npm ERR! A complete log of this run can be found in: /home/user/.npm/_logs/2025-11-07T17_19_17_404Z-debug-0.log

npm ERR! A complete log of this run can be found in: /home/user/.npm/_logs/2025-11-07T17_19_10_175Z-debug-0.log
npm install did not exit successfully
tidy [extra_checks]: IO error: npm install returned exit code exit status: 127
tidy [extra_checks]: FAIL
tidy: The following check failed: extra_checks
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/rust-tidy /checkout /checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 /node/bin/npm --extra-checks=py,cpp,js,spellcheck` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1549:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1279:29

Command has failed. Rerun with -v to see more details.
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Build completed unsuccessfully in 0:02:57
  local time: Fri Nov  7 17:19:37 UTC 2025
  network time: Fri, 07 Nov 2025 17:19:37 GMT
##[error]Process completed with exit code 1.

[JonathanBrouwer]

cfg is quite a perf sensitive attribute since it's used so much, also had problems with it during the port of cfg to the new attribute system. Lets run perf before merging to make sure this doesn't regress compile times.
@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8d673fe (8d673fea7197257987241009c5975c1128b1e405, parent: 843f8ce2ebc01d35a30484eadc8a84cdc6130844)

[rust-timer]

Finished benchmarking commit (8d673fe): comparison URL.

Overall result: ❌ regressions - 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)	0.2%	[0.1%, 0.3%]	14
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	13
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.1%, 0.3%]	14

Max RSS (memory usage)

Results (primary -2.6%, secondary -2.7%)

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)	-	-	0
Improvements ✅ (primary)	-2.6%	[-4.1%, -1.2%]	2
Improvements ✅ (secondary)	-2.7%	[-3.3%, -2.1%]	2
All ❌✅ (primary)	-2.6%	[-4.1%, -1.2%]	2

Cycles

Results (secondary 7.1%)

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)	7.1%	[3.8%, 10.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.6%, secondary 0.4%)

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

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.0%, 2.8%]	77
Regressions ❌ (secondary)	0.4%	[0.1%, 1.6%]	16
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.0%, 2.8%]	77

Bootstrap: 483.325s -> 473.961s (-1.94%)
Artifact size: 390.81 MiB -> 390.81 MiB (-0.00%)

[fmease]

Well that's to be expected as we're strictly doing more work here. Namely, encoding & decoding more attributes (previously, with sym::cfg{,_attr} we didn't encode any attributes IINM as those didn't exist anymore at this stage in the compilation process having been superseded by sym::cfg{,_attr}_trace).

Moreover, this fixes a correctness regression (introduced in #138844), so this is justified. I did look at the perf improvements of the rollup that included the regressing PR (#139023 (comment)) but my findings weren't conclusive (a hypothesis of mine was that we're just reverting the perf improvements of the regressing PR to end up at a net zero).

Anyway, I find the regression justifiable.

@rustbot label perf-regression-triaged

[fmease]

@bors r=GuillaumeGomez

[bors]

📌 Commit 6419f9a has been approved by GuillaumeGomez

It is now in the queue for this repository.

[JonathanBrouwer]

Yep sounds reasonable, just wanted to make sure we are aware of the performance impact when making this change :)