Emit `check-cfg` lints during attribute parsing rather than evaluation #149215

JonathanBrouwer · 2025-11-22T14:39:14Z

The goal of this PR is to make the eval_config_entry not have any side effects, by moving the check-cfg lints to the attribute parsing. This also helps ensure we do emit the lint in situations where the attribute happens to be parsed, but never evaluated.

cc @jdonszelmann @Urgau for a vibe check if you feel like it

Urgau · 2025-11-22T15:09:21Z

Does it mean we would get warnings for non-active cfg attributes?

#[cfg(target_os = "lol")] // warn and not active 
#[cfg(unknown)] // currently doesn't warn, since above is not active, but will it with this PR?
fn foo() {}

Regarding the non-accessible TyCtxt, would it be possible to continue to buffer the lint in ParseSess::buffered_lints, using sess.parse_sess.buffer_lint? Or is the problem that you don't emit the lint as a builtin lint and as such no longer have access to TyCtxt?

JonathanBrouwer · 2025-11-25T19:02:49Z

Attributes that are configured out (like in your example) are currently not parsed, and therefore this would not cause this warning, preserving the old behavior. I didn't think of this edgecase so I'll make sure to add a test for this.

Indeed currently attribute lints are special and not emitted as a builtin lint. I'm gonna play around with this a bit and see if anything is stopping me from changing that

…r=Urgau Run `eval_config_entry` on all branches so we always emit lints Fixes rust-lang#149090 Ideally I'd have liked to fix this issue using rust-lang#149215, and this is still the long term plan, but this is slightly more annoying to implement than I'd have liked to, and this is also a nice and easy solution to the problem. r? `@tgross35`

Rollup merge of #149380 - JonathanBrouwer:cfg_select_lints, r=Urgau Run `eval_config_entry` on all branches so we always emit lints Fixes #149090 Ideally I'd have liked to fix this issue using #149215, and this is still the long term plan, but this is slightly more annoying to implement than I'd have liked to, and this is also a nice and easy solution to the problem. r? `@tgross35`

Run `eval_config_entry` on all branches so we always emit lints Fixes rust-lang/rust#149090 Ideally I'd have liked to fix this issue using rust-lang/rust#149215, and this is still the long term plan, but this is slightly more annoying to implement than I'd have liked to, and this is also a nice and easy solution to the problem. r? `@tgross35`

bors · 2025-11-28T09:40:12Z

☔ The latest upstream changes (presumably #149410) made this pull request unmergeable. Please resolve the merge conflicts.

Run `eval_config_entry` on all branches so we always emit lints Fixes rust-lang/rust#149090 Ideally I'd have liked to fix this issue using rust-lang/rust#149215, and this is still the long term plan, but this is slightly more annoying to implement than I'd have liked to, and this is also a nice and easy solution to the problem. r? `@tgross35`

…elmann Move even more early buffered lints to dyn lint diagnostics Follow-up to #145881 and #145747. I originally wanted to migrate most if not the entire rest of the early buffered lints. However, when trying to migrate the buffered lints used by check-cfg I encountered a roadblock. Namely, it depends on `TyCtxt` (well, `Option<TyCtxt>`) which makes it quite hard to migrate (see also #147634 (comment), #147634 (comment) & #149215). So for now, I won't migrate it (maybe #149215 will find a solution), nor will I migrate the rest since it's quite tedious to migrate these. I'll leave them for future me.

bors · 2025-12-05T02:45:37Z

☔ The latest upstream changes (presumably #149646) made this pull request unmergeable. Please resolve the merge conflicts.

JonathanBrouwer · 2025-12-05T14:16:48Z

Rebased on #149662

After that PR, this change becomes trivial, we don't need to move the lints and we have access to TyCtxt

Urgau

Looks good to me. Thanks for making it impossible to miss the check-cfg diagnostics.

View changes since this review

…nszelmann Move attribute lints to `rustc_lint` This PR changes two things: - This decouples the `AttributeLintKind` from the `Lint` it is emitted in. `cx.emit_lint` now takes both as an argument, rather than inferring the `Lint` from the `AttributeLintKind`. This is nice because: - It allows us to remove `AttributeLintKind::InvalidMacroExportArguments` - It allows us to move the choice between `USELESS_DEPRECATED` and `UNUSED_ATTRIBUTES` out of the lint emitting code - It allows the next change: - This moves `AttributeLintKind` to `rustc_lint_defs`, and the decorating code to `rustc_lint`. This is nice because: - It allows attribute lint decorating code to access the TypeCtxt, which unblocks rust-lang#149215 - It might allow most early buffered attribute lints to become dyn lint diagnostics in the future, as in rust-lang#147634 - It deduplicates `IllFormedAttributeInput` This PR does not change observable output of the compiler, as can be seen by no uitests being affected. r? `@jdonszelmann`

Rollup merge of #149662 - JonathanBrouwer:lint-rework, r=jdonszelmann Move attribute lints to `rustc_lint` This PR changes two things: - This decouples the `AttributeLintKind` from the `Lint` it is emitted in. `cx.emit_lint` now takes both as an argument, rather than inferring the `Lint` from the `AttributeLintKind`. This is nice because: - It allows us to remove `AttributeLintKind::InvalidMacroExportArguments` - It allows us to move the choice between `USELESS_DEPRECATED` and `UNUSED_ATTRIBUTES` out of the lint emitting code - It allows the next change: - This moves `AttributeLintKind` to `rustc_lint_defs`, and the decorating code to `rustc_lint`. This is nice because: - It allows attribute lint decorating code to access the TypeCtxt, which unblocks #149215 - It might allow most early buffered attribute lints to become dyn lint diagnostics in the future, as in #147634 - It deduplicates `IllFormedAttributeInput` This PR does not change observable output of the compiler, as can be seen by no uitests being affected. r? `@jdonszelmann`

…n#149215

rustbot · 2025-12-06T09:39:10Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann

JonathanBrouwer · 2025-12-06T09:39:38Z

The PR is ready to be merged now :)

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JonathanBrouwer force-pushed the cfg_lints2 branch from abb82ad to 4ee0f66 Compare November 22, 2025 15:21

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JonathanBrouwer force-pushed the cfg_lints2 branch from 4ee0f66 to f5e9e93 Compare November 22, 2025 19:55

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JonathanBrouwer mentioned this pull request Nov 27, 2025

Run eval_config_entry on all branches so we always emit lints #149380

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fmease mentioned this pull request Nov 30, 2025

Move even more early buffered lints to dyn lint diagnostics #147634

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JonathanBrouwer force-pushed the cfg_lints2 branch from f5e9e93 to 1b85568 Compare December 4, 2025 19:27

JonathanBrouwer mentioned this pull request Dec 4, 2025

Move attribute lints to rustc_lint #149662

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JonathanBrouwer force-pushed the cfg_lints2 branch from 1b85568 to 557fcb0 Compare December 5, 2025 14:13

JonathanBrouwer added the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Dec 5, 2025

JonathanBrouwer force-pushed the cfg_lints2 branch from 557fcb0 to 5010285 Compare December 5, 2025 14:15

JonathanBrouwer changed the title ~~Move check-cfg lints to rustc_attr_parsing~~ Emit check-cfg during attribute parsing rather than evaluation Dec 5, 2025

JonathanBrouwer changed the title ~~Emit check-cfg during attribute parsing rather than evaluation~~ Emit check-cfg lints during attribute parsing rather than evaluation Dec 5, 2025

JonathanBrouwer force-pushed the cfg_lints2 branch from 5010285 to b93aaa7 Compare December 5, 2025 14:23

jdonszelmann self-assigned this Dec 5, 2025

Urgau self-assigned this Dec 5, 2025

Urgau approved these changes Dec 5, 2025

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JonathanBrouwer added 2 commits December 6, 2025 10:22

Emit check-cfg lints during attribute parsing rather than evaluatio…

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…n#149215

Changes to uitests

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JonathanBrouwer force-pushed the cfg_lints2 branch from b93aaa7 to e7df904 Compare December 6, 2025 09:25

Add regression test for nested cfgs

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JonathanBrouwer marked this pull request as ready for review December 6, 2025 09:39

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 Dec 6, 2025

JonathanBrouwer removed the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Dec 6, 2025

JonathanBrouwer mentioned this pull request Dec 6, 2025

Port doc attributes to new attribute API #149645

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Emit `check-cfg` lints during attribute parsing rather than evaluation #149215

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