Port `cfg_select!` to the new attribute parsing system by JonathanBrouwer · Pull Request #148712 · rust-lang/rust

JonathanBrouwer · 2025-11-08T20:45:44Z

Best reviewed commit by commit, since it involves some moving around of code

r? @jdonszelmann

rustbot · 2025-11-08T20:45:47Z

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann

rustbot · 2025-11-08T20:45:50Z

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

compiler/rustc_parse/src/parser/cfg_select.rs

JonathanBrouwer · 2025-11-09T12:33:44Z

@rustbot author
Need to address Folkert's comment

rustbot · 2025-11-09T12:33:48Z

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

rustbot · 2025-11-09T14:51:55Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

JonathanBrouwer · 2025-11-09T14:52:49Z

@rustbot ready
Made the changes so this code is usable from rustfmt. I believe you should be able to call parse_cfg_select.

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

rustbot · 2025-11-09T15:11:25Z

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.

jdonszelmann · 2025-11-10T10:14:13Z

compiler/rustc_attr_parsing/src/attributes/cfg_select.rs

+) -> Result<CfgSelectBranches, ErrorGuaranteed> {
+    let mut branches = CfgSelectBranches::default();
+
+    while p.token != token::Eof {


this makes me so sad but for now we'll have to...

jdonszelmann · 2025-11-10T10:41:56Z

@bors r+ rollup

bors · 2025-11-10T10:41:59Z

📌 Commit 90f36af has been approved by jdonszelmann

It is now in the queue for this repository.

bors · 2025-11-10T10:42:00Z

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

…szelmann Port `cfg_select!` to the new attribute parsing system Best reviewed commit by commit, since it involves some moving around of code r? ``@jdonszelmann``

…szelmann Port `cfg_select!` to the new attribute parsing system Best reviewed commit by commit, since it involves some moving around of code r? ```@jdonszelmann```

Rollup of 9 pull requests Successful merges: - #148480 (Add `Steal::risky_hack_borrow_mut`) - #148608 (Add test for --test-builder success path) - #148667 (a few small clippy fixes) - #148712 (Port `cfg_select!` to the new attribute parsing system) - #148760 (rustc_target: hide TargetOptions::vendor) - #148775 (Fix a typo in the documentation for the strict_shr function) - #148779 (Implement DynSend and DynSync for std::panic::Location.) - #148781 ([rustdoc] Remove unneeded `allow(rustc::potential_query_instability)`) - #148791 (fix "is_closure_like" doc comment) r? `@ghost` `@rustbot` modify labels: rollup

…szelmann Port `cfg_select!` to the new attribute parsing system Best reviewed commit by commit, since it involves some moving around of code r? ````@jdonszelmann````

Rollup of 13 pull requests Successful merges: - #148694 (std: support `RwLock` and thread parking on TEEOS) - #148712 (Port `cfg_select!` to the new attribute parsing system) - #148760 (rustc_target: hide TargetOptions::vendor) - #148771 (IAT: Reinstate early bailout) - #148775 (Fix a typo in the documentation for the strict_shr function) - #148779 (Implement DynSend and DynSync for std::panic::Location.) - #148781 ([rustdoc] Remove unneeded `allow(rustc::potential_query_instability)`) - #148783 (add test for assoc type norm wf check) - #148785 (Replace `master` branch references with `main`) - #148791 (fix "is_closure_like" doc comment) - #148792 (Prefer to use file.stable_id over file.name from source map) - #148805 (rustc-dev-guide subtree update) - #148807 (Document (and test) a problem with `Clone`/`Copy` deriving.) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #148712 - JonathanBrouwer:cfg_select, r=jdonszelmann Port `cfg_select!` to the new attribute parsing system Best reviewed commit by commit, since it involves some moving around of code r? `````@jdonszelmann`````

Rollup of 13 pull requests Successful merges: - rust-lang/rust#148694 (std: support `RwLock` and thread parking on TEEOS) - rust-lang/rust#148712 (Port `cfg_select!` to the new attribute parsing system) - rust-lang/rust#148760 (rustc_target: hide TargetOptions::vendor) - rust-lang/rust#148771 (IAT: Reinstate early bailout) - rust-lang/rust#148775 (Fix a typo in the documentation for the strict_shr function) - rust-lang/rust#148779 (Implement DynSend and DynSync for std::panic::Location.) - rust-lang/rust#148781 ([rustdoc] Remove unneeded `allow(rustc::potential_query_instability)`) - rust-lang/rust#148783 (add test for assoc type norm wf check) - rust-lang/rust#148785 (Replace `master` branch references with `main`) - rust-lang/rust#148791 (fix "is_closure_like" doc comment) - rust-lang/rust#148792 (Prefer to use file.stable_id over file.name from source map) - rust-lang/rust#148805 (rustc-dev-guide subtree update) - rust-lang/rust#148807 (Document (and test) a problem with `Clone`/`Copy` deriving.) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 13 pull requests Successful merges: - rust-lang#148694 (std: support `RwLock` and thread parking on TEEOS) - rust-lang#148712 (Port `cfg_select!` to the new attribute parsing system) - rust-lang#148760 (rustc_target: hide TargetOptions::vendor) - rust-lang#148771 (IAT: Reinstate early bailout) - rust-lang#148775 (Fix a typo in the documentation for the strict_shr function) - rust-lang#148779 (Implement DynSend and DynSync for std::panic::Location.) - rust-lang#148781 ([rustdoc] Remove unneeded `allow(rustc::potential_query_instability)`) - rust-lang#148783 (add test for assoc type norm wf check) - rust-lang#148785 (Replace `master` branch references with `main`) - rust-lang#148791 (fix "is_closure_like" doc comment) - rust-lang#148792 (Prefer to use file.stable_id over file.name from source map) - rust-lang#148805 (rustc-dev-guide subtree update) - rust-lang#148807 (Document (and test) a problem with `Clone`/`Copy` deriving.) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 13 pull requests Successful merges: - rust-lang/rust#148694 (std: support `RwLock` and thread parking on TEEOS) - rust-lang/rust#148712 (Port `cfg_select!` to the new attribute parsing system) - rust-lang/rust#148760 (rustc_target: hide TargetOptions::vendor) - rust-lang/rust#148771 (IAT: Reinstate early bailout) - rust-lang/rust#148775 (Fix a typo in the documentation for the strict_shr function) - rust-lang/rust#148779 (Implement DynSend and DynSync for std::panic::Location.) - rust-lang/rust#148781 ([rustdoc] Remove unneeded `allow(rustc::potential_query_instability)`) - rust-lang/rust#148783 (add test for assoc type norm wf check) - rust-lang/rust#148785 (Replace `master` branch references with `main`) - rust-lang/rust#148791 (fix "is_closure_like" doc comment) - rust-lang/rust#148792 (Prefer to use file.stable_id over file.name from source map) - rust-lang/rust#148805 (rustc-dev-guide subtree update) - rust-lang/rust#148807 (Document (and test) a problem with `Clone`/`Copy` deriving.) r? `@ghost` `@rustbot` modify labels: rollup

@traviscross

…=JonathanBrouwer stabilize `cfg_select!` *[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/149783)* tracking issue: rust-lang#115585 closes rust-lang#115585 reference PR: - rust-lang/reference#2103 # Request for Stabilization ## Summary The `cfg_select!` macro picks the expansion corresponding to the first `cfg` condition that evaluates to `true`. It simplifies complex conditional expressions. ```rust cfg_select! { unix => { fn foo() { /* unix specific functionality */ } } target_pointer_width = "32" => { fn foo() { /* non-unix, 32-bit functionality */ } } _ => { fn foo() { /* fallback implementation */ } } } let is_unix_str = cfg_select! { unix => "unix", _ => "not unix", }; println!("{is_unix_str}"); ``` ## Semantics The expansion of a `cfg_select!` call is the right-hand side of the first `cfg` rule that evaluates to true. This can be roughly expressed using this macro: ```rust macro_rules! cfg_select { ({ $($tt:tt)* }) => {{ $crate::cfg_select! { $($tt)* } }}; (_ => { $($output:tt)* }) => { $($output)* }; ( $cfg:meta => $output:tt $($( $rest:tt )+)? ) => { #[cfg($cfg)] $crate::cfg_select! { _ => $output } $( #[cfg(not($cfg))] $crate::cfg_select! { $($rest)+ } )? } } ``` The actual implementation uses a builtin macro so that `cfg_select!` can be used both in item and expression position. ## Documentation reference PR: - rust-lang/reference#2103 ## Tests The `cfg_select!` macro is already used extensively in the rust compiler codebase. It has several dedicated tests: - [`tests/ui/check-cfg/cfg-select.rs`](https://github.com/rust-lang/rust/blob/main/tests/ui/check-cfg/cfg-select.rs)tests that warnings are emitted when an unexpected `cfg` condition is used. - [`tests/ui/macros/cfg_select.rs`](https://github.com/rust-lang/rust/blob/main/tests/ui/macros/cfg_select.rs) tests that `cfg_select!` has the expected expansion, and tests that the expected syntax is accepted. ## History - rust-lang#115416 - rust-lang#117162 - rust-lang#133720 - rust-lang#135625 - rust-lang#137198 - rust-lang#138993 - rust-lang#138996 - rust-lang#143461 - rust-lang#143941 - rust-lang#145233 - rust-lang#148712 - rust-lang#149380 - rust-lang#149925 # Resolved questions # Unresolved questions The style team has decided on how to format `cfg_select!`, but this formatting has not yet been implemented. See rust-lang#144323. r? @traviscross   > [!NOTE] > # Concerns (0 active) > > - ~~[allowing-comma-after-closing-brace](rust-lang#149783 (comment) resolved in [this comment](rust-lang#149783 (comment)) > > *Managed by `@rustbot`—see [help](https://forge.rust-lang.org/triagebot/concern.html) for details.*

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 Nov 8, 2025

rustbot assigned jdonszelmann Nov 8, 2025

folkertdev reviewed Nov 9, 2025

View reviewed changes

compiler/rustc_parse/src/parser/cfg_select.rs Show resolved Hide resolved

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 9, 2025

JonathanBrouwer force-pushed the cfg_select branch from 1125b68 to cf6d5c1 Compare November 9, 2025 14:51

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 Nov 9, 2025

This comment has been minimized.

Sign in to view

JonathanBrouwer added 3 commits November 9, 2025 16:08

Move parse_cfg_select to rustc_builtin_macros

a5814a5

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

Add more tests for cfg_select parsing

c111ccc

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

Port cfg_select! to the new attribute parsing system

90f36af

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

JonathanBrouwer force-pushed the cfg_select branch from cf6d5c1 to 90f36af Compare November 9, 2025 15:11

jdonszelmann reviewed Nov 10, 2025

View reviewed changes

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 Nov 10, 2025

ChrisDenton mentioned this pull request Nov 10, 2025

Rollup of 14 pull requests #148800

Closed

JonathanBrouwer mentioned this pull request Nov 10, 2025

Handle macro invocation in attribute during parse #146579

Merged

ChrisDenton mentioned this pull request Nov 10, 2025

Rollup of 9 pull requests #148802

Closed

Zalathar mentioned this pull request Nov 11, 2025

Rollup of 13 pull requests #148818

Merged

bors merged commit e26b423 into rust-lang:main Nov 11, 2025
11 checks passed

rustbot added this to the 1.93.0 milestone Nov 11, 2025

JonathanBrouwer mentioned this pull request Nov 19, 2025

cfg_select should check for unexpected_cfgs on other arms #149090

Closed

folkertdev added the F-cfg_select `#![feature(cfg_select)]` label Dec 8, 2025

folkertdev mentioned this pull request Dec 8, 2025

stabilize cfg_select! #149783

Open

Uh oh!

Comments

Conversation

JonathanBrouwer commented Nov 8, 2025

Uh oh!

rustbot commented Nov 8, 2025

Uh oh!

rustbot commented Nov 8, 2025

Uh oh!

Uh oh!

JonathanBrouwer commented Nov 9, 2025

Uh oh!

rustbot commented Nov 9, 2025

Uh oh!

rustbot commented Nov 9, 2025

Uh oh!

JonathanBrouwer commented Nov 9, 2025

Uh oh!

This comment has been minimized.

rustbot commented Nov 9, 2025

Uh oh!

jdonszelmann Nov 10, 2025

Choose a reason for hiding this comment

Uh oh!

jdonszelmann commented Nov 10, 2025

Uh oh!

bors commented Nov 10, 2025

Uh oh!

bors commented Nov 10, 2025

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants