Track items behind `cfg_select` in the same way we do for `cfg` by estebank · Pull Request #157218 · rust-lang/rust

estebank · 2026-05-31T19:22:56Z

When annotating an item with #[cfg] we track both the item that got annotated (with an inert attr) and the names of items that got directly cfg'd out. Extend this mechanism to also work for items within a cfg_select!.

r? @jdonszelmann
cc @JonathanBrouwer

rustbot · 2026-05-31T19:22:59Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

rustbot · 2026-05-31T19:23:01Z

jdonszelmann is currently at their maximum review capacity.
They may take a while to respond.

estebank · 2026-05-31T19:23:58Z

This or something akin to this is needed for #129249. I'll clean up the code shortly, once I get that PR to the point it can run on crater.

rustbot · 2026-06-01T00:58:30Z

The Cranelift subtree was changed

cc @bjorn3

petrochenkov · 2026-06-01T14:33:20Z

(I'd like to look at this, probably tomorrow, because the PR touches expansion infra.)

estebank · 2026-06-19T21:51:03Z

Gentle ping :)

JonathanBrouwer · 2026-08-20T14:29:48Z

r? me
I can take a look at this this weekend

JonathanBrouwer · 2026-08-20T19:22:20Z

+   | |                     ^^^^^^^^^^^^
+...  |
+LL | |         _ => {}
+   | |_________- the item is gated here


Hmmm, I find the "the item is gated here" a bit wide, how hard would it be to make it point only to the cfg predicate?

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Bonus point if we can point to the reason_span that is returned when attr::eval_config_entry returns EvalConfigResult::False, I worked hard to make that information available :)

@JonathanBrouwer I think we'll need a larger change to make use of reason_span here. I noticed there are quite a few places where we immediately call .as_bool(), which completely discards that information and that might be a good place to look for further improvements.

JonathanBrouwer

Other than that, this looks good :)
Sorry that this took so long to get reviewed, this is awesome work!

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rustbot · 2026-08-20T19:25:19Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

When annotating an item with `#[cfg]` we track both the item that got annotated (with an inert attr) and the names of items that got directly cfg'd out. Extend this mechanism to also work for items within a `cfg_select!`.

rustbot · 2026-08-26T20:09:28Z

This PR was rebased onto a different main 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

@bors r+ rollup
This is already a large improvement so lets get this merged.
I put it on my todo list to look at reason_span here.

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rust-bors · 2026-08-28T07:36:25Z

📌 Commit ce74313 has been approved by JonathanBrouwer

It is now in the queue for this repository.

…uwer Rollup of 21 pull requests Successful merges: - #150075 (Implement clamp_to) - #159103 (fix(reborrow): recursive implementation) - #160562 (add target feature ABI checks for SPARC) - #160848 (std: avoid aliasing violations when wrapping opaque C types) - #161421 (Include startup crt objects on WASI for more outputs) - #161805 (Prefer ambiguous candidates when deduplicating traits in scope, so `ambiguous_glob_imported_traits` doesn't depend on import order) - #161862 (Put data segment in specified section with link_section on wasm) - #161866 (delegation: add tests fixating behavior of delegating to default trait implementations) - #157218 (Track items behind `cfg_select` in the same way we do for `cfg`) - #161456 (reduce perf impact of scalar size checks) - #161528 (Add regression test to ensure optimal compilation) - #161666 (Print vendor instructions in `x vendor`) - #161730 (Improve type mismatch annotation for lets with block-wrapped initializers) - #161828 (Never type after-stabilization cleanup) - #161859 (Do not optimize MIR for comptime ConstFns) - #161860 (atomicptr.rs test: remove unused import) - #161870 (bind to [::1] instead of 127.0.0.1 in documentation examples for v6 UDP methods) - #161876 (rustdoc: Correctly handle when a macro generates multiple items in `--generate-macro-expansion`) - #161889 (Add link to ownership section in ptr::read docs) - #161890 (rustdoc: some clarifying comments) - #161891 (Mark `extern_item_impls` feature as incomplete) Failed merges: - #161702 (Use `drop_guard` in some places in {core,alloc,std})

@jdonszelmann

Rollup merge of #157218 - estebank:cfg_select_tracking, r=JonathanBrouwer Track items behind `cfg_select` in the same way we do for `cfg` When annotating an item with `#[cfg]` we track both the item that got annotated (with an inert attr) and the names of items that got directly cfg'd out. Extend this mechanism to also work for items within a `cfg_select!`. r? @jdonszelmann cc @JonathanBrouwer

rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) 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. labels May 31, 2026

rustbot assigned jdonszelmann May 31, 2026

estebank force-pushed the cfg_select_tracking branch from 2262d01 to 97da0c8 Compare June 1, 2026 00:59

petrochenkov self-assigned this Jun 1, 2026

estebank commented Jun 1, 2026

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Comment thread compiler/rustc_expand/src/expand.rs

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Comment thread compiler/rustc_expand/src/expand.rs

Comment thread compiler/rustc_builtin_macros/src/cfg_select.rs Outdated

Comment thread compiler/rustc_builtin_macros/src/cfg_select.rs Outdated

Comment thread compiler/rustc_builtin_macros/src/cfg_select.rs Outdated

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estebank force-pushed the cfg_select_tracking branch from 76ed1df to 34c1685 Compare June 3, 2026 18:22

estebank 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 Jun 3, 2026

estebank mentioned this pull request Jun 3, 2026

<T as Into<T>>::into lint #129249

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estebank force-pushed the cfg_select_tracking branch from 34c1685 to a04d12d Compare June 3, 2026 21:46

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estebank force-pushed the cfg_select_tracking branch from eea0055 to 89a11d2 Compare June 19, 2026 22:55

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Track items behind cfg_select in the same way we do for cfg

ce74313

When annotating an item with `#[cfg]` we track both the item that got annotated (with an inert attr) and the names of items that got directly cfg'd out. Extend this mechanism to also work for items within a `cfg_select!`.

estebank force-pushed the cfg_select_tracking branch from 89a11d2 to ce74313 Compare August 26, 2026 20:09

estebank 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 Aug 27, 2026

JonathanBrouwer approved these changes Aug 28, 2026

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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 Aug 28, 2026

JonathanBrouwer mentioned this pull request Aug 28, 2026

Rollup of 21 pull requests #161906

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rust-bors Bot merged commit 91c9639 into rust-lang:main Aug 28, 2026
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rustbot added this to the 1.100.0 milestone Aug 28, 2026

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