rustfmt: Format `cfg_select!` by ytmimi · Pull Request #154202 · rust-lang/rust

ytmimi · 2026-03-22T05:04:25Z

tracking issue: #115585

Implementing cfg_select! formatting here in rust-lang/rust so that the feature can get out to nightly quicker.
The previous PR (#144323) is a bit old at this point and I felt like I could simplify the implementation so I've opted to reimplement the formatting instead of building off the previous PR.

I've tried to break the PR up into logical commits and I think this would be best reviewed one commit at a time.

Previous PR:

add rustfmt support for cfg_select #144323

See also:

Formatting for cfg_select style-team#201

rustbot · 2026-03-22T05:04:29Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

rustbot · 2026-03-22T05:04:31Z

r? @jieyouxu

rustbot has assigned @jieyouxu.
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Owners of files modified in this PR: rustfmt, rustfmt-contributors
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Random selection from fee1-dead, jieyouxu

ytmimi · 2026-03-22T05:08:45Z

+// trailing comments on the last line are a little buggy and always wrap back up
+cfg_select! {
+ windows => {
+ "windows"
+ }
+ unix => {
+ "unix"
+ }
+ _ => {
+ "none"
+ } // FIXME. Prevent wrapping back up to the next line
+}
+
+cfg_select! {
+ windows => "windows",
+ unix => "unix",
+ _ => "none", // FIXME. Prevent wrapping back up to the next line
+}


A pre-existing issue with trailing comments in rustfmt. I wanted to explicitly capture the current behavior in a test case.

ytmimi · 2026-03-22T05:10:36Z

+// Can't format cfg_select! at all with style_edition <= 2021.
+// Things can be formatted with style_edition >= 2024
+cfg_select! {
+ feature = "debug-with-rustfmt-long-long-long-long-loooooooonnnnnnnnnnnnnnnggggggffffffffffffffff" =>
+ {
+ // abc
+ println!();
+ }
+ feature = "debug-with-rustfmt-long-long-long-long-loooooooonnnnnnnnnnnnnnnggggggffffffffffffffff" =>
+ {
+ // abc
+ }
+ all(anything(
+ "some other long long long long long thing long long long long long long long long long long long",
+ feature = "debug-with-rustfmt-long-long-long-long-loooooooonnnnnnnnnnnnnnnggggggffffffffffffffff"
+ )) => {
+ let x = 7;
+ }
+}


Through some testing I found that in style_edition <= 2021 this example won't be formatted at all because the predicate can't be formatted within max_width, but with style_edition >= 2024 that's not an issue.

ytmimi · 2026-03-22T05:17:06Z

+// comments within the predicate are fine with style_edition=2024+
+cfg_select! {
+ any(
+ true, /* comment */
+ true, true, // true,
+ true,
+ ) => {}
+
+ not(
+ false // comment
+ ) => {}
+
+ any(
+ false // comment
+ ) => "any",
+}


Not the best place for a comment to begin with IMO, but I wanted to call out that comments within the predicate aren't correctly handled in style_edition <= 2021. This is how the current example is formatted:
cfg_select!{ any(true,/* comment */true,true,// true,true,) => {} not(false// comment) => {} any(false// comment) => "any",}
Clearly that's wrong and produces invalid code, but fixing this seems like it's outisde the scope of this PR. since it only impacts style_edition <= 2021.
Maybe this is something we can address later?

I agree, I think we shouldn't try to bundle that in this PR. We probably should open an issue in rustfmt/r-l/r to track this as a known-bug though.

folkertdev

Extremely happy to see this!

View changes since this review

jieyouxu · 2026-03-23T06:10:57Z

(I'll gradually review this; need to build up some background ctx first.)

jieyouxu

Thanks! The impl broadly looks good to me, just some minor nits and a few test coverage discussions.
@rustbot author

View changes since this review

jieyouxu · 2026-03-30T02:48:31Z

+// comments within the predicate are fine with style_edition=2024+
+cfg_select! {
+ any(
+ true, /* comment */
+ true, true, // true,
+ true,
+ ) => {}
+
+ not(
+ false // comment
+ ) => {}
+
+ any(
+ false // comment
+ ) => "any",
+}


I agree, I think we shouldn't try to bundle that in this PR. We probably should open an issue in rustfmt/r-l/r to track this as a known-bug though.

jieyouxu · 2026-03-30T02:49:26Z

+// comments before and after the `=>` get dropped right now
+cfg_select! {
+ any(true, true, true, true,) => {}
+
+ not(false) => {}
+
+ any(false) => "any",
+}


Question: this should also a "known bug" right? Should we also include a follow-up issue to track this?

Yeah, I think we can create an issue for it. I'll handle that after the initial formatting lands

rustbot · 2026-03-30T03:04:15Z

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

jieyouxu · 2026-03-30T08:30:16Z

Backlinks / context for myself (and future travellers):
Metadata
Library feature: cfg_select
std docs: https://doc.rust-lang.org/nightly/std/macro.cfg_select.html
Tracking issue: Tracking issue for cfg_select (formerly cfg_match) #115585
Style team discussion: Formatting for cfg_select style-team#201
Reference update PR: cfg_select! macro reference#2103
History
Initial style team discussions
The arms must be wrapped in braces, so rustfmt will have to ensure to not remove those.
Follow-up: unbraced expressions are permitted
PR: #145233

@ytmimi

…es, r=ytmimi,jieyouxu rustfmt: Discover modules via `cfg_select!` This PR renames all occurrences of `cfg_match!` in rustfmt to `cfg_select!`. This makes the module file detection logic from rust-lang/rustfmt#6522 kick in for `cfg_select!` instead of `cfg_match!`, which no longer exists. This PR performs no other adjustments to the logic to be as small as possible. I am opening this PR in this repo since that is also the target for the more comprehensive rust-lang#154202, which covers more than merely detecting other files through `cfg_select!`. Closesrust-lang#158371. CC: @ytmimi, @CAD97

@ytmimi

Rollup merge of #158372 - mkroening:rustfmt-cfg_select-modules, r=ytmimi,jieyouxu rustfmt: Discover modules via `cfg_select!` This PR renames all occurrences of `cfg_match!` in rustfmt to `cfg_select!`. This makes the module file detection logic from rust-lang/rustfmt#6522 kick in for `cfg_select!` instead of `cfg_match!`, which no longer exists. This PR performs no other adjustments to the logic to be as small as possible. I am opening this PR in this repo since that is also the target for the more comprehensive #154202, which covers more than merely detecting other files through `cfg_select!`. Closes#158371. CC: @ytmimi, @CAD97

@ytmimi

…imi,jieyouxu rustfmt: Discover modules via `cfg_select!` This PR renames all occurrences of `cfg_match!` in rustfmt to `cfg_select!`. This makes the module file detection logic from rust-lang/rustfmt#6522 kick in for `cfg_select!` instead of `cfg_match!`, which no longer exists. This PR performs no other adjustments to the logic to be as small as possible. I am opening this PR in this repo since that is also the target for the more comprehensive rust-lang/rust#154202, which covers more than merely detecting other files through `cfg_select!`. Closesrust-lang/rust#158371. CC: @ytmimi, @CAD97

`cfg_select!` parsing needs to be implemented in rustfmt right now because there's no good way to call `rustc_attr_parsing::parse_cfg_select`.

The plan is to leverage `rewrite_match_body` to help with `cfg_select!` formatting.

…andling

jieyouxu

Thanks @ytmimi!

@bors r+ rollup

View changes since this review

jieyouxu · 2026-07-31T04:48:54Z

+// Doesn't parse as expected so this is handled by the default macro handling
+cfg_select! (
+ A + B + C
+);
+cfg_select! [
+ A + B + C
+];
+// rustfmt doesn't format macros with brace delimiters
+cfg_select! {
+ A + B + C
+}


Remark: good call, I forgot about this coverage

rust-bors · 2026-07-31T04:49:26Z

📌 Commit ca398cd has been approved by jieyouxu

It is now in the queue for this repository.

rustfmt: Format `cfg_select!` tracking issue: rust-lang#115585 Implementing `cfg_select!` formatting here in `rust-lang/rust` so that the feature can get out to nightly quicker. The previous PR (rust-lang#144323) is a bit old at this point and I felt like I could simplify the implementation so I've opted to reimplement the formatting instead of building off the previous PR. I've tried to break the PR up into logical commits and I think this would be best reviewed one commit at a time. --- Previous PR: * rust-lang#144323 See also: * rust-lang/style-team#201

…uwer Rollup of 21 pull requests Successful merges: - #160100 (Add "system" option to `override-allocator` directive) - #159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - #159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - #160233 (Bubble bad path error while parsing field to avoid unecessary second error) - #160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - #154202 (rustfmt: Format `cfg_select!`) - #158835 (rustc_passes: lint unused `#[path]` attributes on inline modules) - #159520 (Suggest `Vec<T>` instead of `[T]`) - #160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - #160066 (rustc_middle: lint attribute cleanups) - #160085 (Remove various superfluous lint attributes) - #160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - #160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - #160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - #160157 (Remove outdated comments from `va_list.rs`) - #160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - #160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - #160244 (Rename splat to rustc_splat in error messages) - #160246 (dont fire `unused_mut` on `&pin mut self`) - #160247 (Configure backport nominations for rustfmt) - #160274 (renovate: update lock files weekly)

…uwer Rollup of 22 pull requests Successful merges: - #160100 (Add "system" option to `override-allocator` directive) - #160220 (Refactor: shrink region ext traits) - #159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - #159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - #160233 (Bubble bad path error while parsing field to avoid unecessary second error) - #160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - #154202 (rustfmt: Format `cfg_select!`) - #159520 (Suggest `Vec<T>` instead of `[T]`) - #159710 (Add rustdoc/cargo PGO profiles to reproducible artifacts) - #160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - #160066 (rustc_middle: lint attribute cleanups) - #160085 (Remove various superfluous lint attributes) - #160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - #160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - #160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - #160157 (Remove outdated comments from `va_list.rs`) - #160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - #160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - #160244 (Rename splat to rustc_splat in error messages) - #160246 (dont fire `unused_mut` on `&pin mut self`) - #160247 (Configure backport nominations for rustfmt) - #160274 (renovate: update lock files weekly)

Rollup merge of #154202 - ytmimi:format_cfg_select, r=jieyouxu rustfmt: Format `cfg_select!` tracking issue: #115585 Implementing `cfg_select!` formatting here in `rust-lang/rust` so that the feature can get out to nightly quicker. The previous PR (#144323) is a bit old at this point and I felt like I could simplify the implementation so I've opted to reimplement the formatting instead of building off the previous PR. I've tried to break the PR up into logical commits and I think this would be best reviewed one commit at a time. --- Previous PR: * #144323 See also: * rust-lang/style-team#201

…uwer Rollup of 22 pull requests Successful merges: - rust-lang/rust#160100 (Add "system" option to `override-allocator` directive) - rust-lang/rust#160220 (Refactor: shrink region ext traits) - rust-lang/rust#159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - rust-lang/rust#159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - rust-lang/rust#160233 (Bubble bad path error while parsing field to avoid unecessary second error) - rust-lang/rust#160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - rust-lang/rust#154202 (rustfmt: Format `cfg_select!`) - rust-lang/rust#159520 (Suggest `Vec<T>` instead of `[T]`) - rust-lang/rust#159710 (Add rustdoc/cargo PGO profiles to reproducible artifacts) - rust-lang/rust#160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - rust-lang/rust#160066 (rustc_middle: lint attribute cleanups) - rust-lang/rust#160085 (Remove various superfluous lint attributes) - rust-lang/rust#160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - rust-lang/rust#160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - rust-lang/rust#160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - rust-lang/rust#160157 (Remove outdated comments from `va_list.rs`) - rust-lang/rust#160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - rust-lang/rust#160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - rust-lang/rust#160244 (Rename splat to rustc_splat in error messages) - rust-lang/rust#160246 (dont fire `unused_mut` on `&pin mut self`) - rust-lang/rust#160247 (Configure backport nominations for rustfmt) - rust-lang/rust#160274 (renovate: update lock files weekly)

@jieyouxu

…matting, r=jieyouxu rustfmt: restrict `cfg_select!` formatting to the `nightly` release channel Closes: rust-lang#160944 `cfg_select!` formatting was implemented in rust-lang#154202. The formatting diverged from what was outlined in the original Style FCP (rust-lang/style-team#201 (comment) and rust-lang#144323 (comment)). Since the 1.99 beta is scheduled to branch from main on August 14 I want to get this nightly formatting gate out so that we can correct the formatting issues before we promote the formatting to the beta / stable release channels. Style Guide PR: rust-lang#160967 r? @jieyouxu cc: @traviscross

@jieyouxu

Rollup merge of #160998 - ytmimi:nightly_only_cfg_select_formatting, r=jieyouxu rustfmt: restrict `cfg_select!` formatting to the `nightly` release channel Closes: #160944 `cfg_select!` formatting was implemented in #154202. The formatting diverged from what was outlined in the original Style FCP (rust-lang/style-team#201 (comment) and #144323 (comment)). Since the 1.99 beta is scheduled to branch from main on August 14 I want to get this nightly formatting gate out so that we can correct the formatting issues before we promote the formatting to the beta / stable release channels. Style Guide PR: #160967 r? @jieyouxu cc: @traviscross

…uwer Rollup of 22 pull requests Successful merges: - rust-lang/rust#160100 (Add "system" option to `override-allocator` directive) - rust-lang/rust#160220 (Refactor: shrink region ext traits) - rust-lang/rust#159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - rust-lang/rust#159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - rust-lang/rust#160233 (Bubble bad path error while parsing field to avoid unecessary second error) - rust-lang/rust#160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - rust-lang/rust#154202 (rustfmt: Format `cfg_select!`) - rust-lang/rust#159520 (Suggest `Vec<T>` instead of `[T]`) - rust-lang/rust#159710 (Add rustdoc/cargo PGO profiles to reproducible artifacts) - rust-lang/rust#160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - rust-lang/rust#160066 (rustc_middle: lint attribute cleanups) - rust-lang/rust#160085 (Remove various superfluous lint attributes) - rust-lang/rust#160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - rust-lang/rust#160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - rust-lang/rust#160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - rust-lang/rust#160157 (Remove outdated comments from `va_list.rs`) - rust-lang/rust#160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - rust-lang/rust#160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - rust-lang/rust#160244 (Rename splat to rustc_splat in error messages) - rust-lang/rust#160246 (dont fire `unused_mut` on `&pin mut self`) - rust-lang/rust#160247 (Configure backport nominations for rustfmt) - rust-lang/rust#160274 (renovate: update lock files weekly)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-rustfmt Relevant to the rustfmt team, which will review and decide on the PR/issue. labels Mar 22, 2026

rustbot assigned jieyouxu Mar 22, 2026

ytmimi commented Mar 22, 2026
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Comment threadsrc/tools/rustfmt/tests/target/cfg_select.rs Outdated

ytmimi commented Mar 22, 2026
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folkertdev mentioned this pull request Mar 22, 2026
add rustfmt support for cfg_select#144323
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Comment threadsrc/tools/rustfmt/tests/source/cfg_select.rs

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This was referenced Jun 24, 2026
rustfmt does not discover modules through cfg_select!#158371
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rustfmt: Discover modules via cfg_select!#158372
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ytmimi added 6 commits July 30, 2026 00:25

feat: parse cfg_select! within rustfmt
8c8a3d7
`cfg_select!` parsing needs to be implemented in rustfmt right now because there's no good way to call `rustc_attr_parsing::parse_cfg_select`.

chore: make rewrite_match_bodypub(crate) within rustfmt
65fb2bb
The plan is to leverage `rewrite_match_body` to help with `cfg_select!` formatting.

feat: implement cfg_select! formatting in rustfmt
ea47e34

test: Add more cfg_select! test cases based on the PR review feedback
a932a6d

docs: Add doc comments based on PR feedback
d18984c

feat: flatten cfg_select! arms if they're a single expression
d32c7e9

ytmimi force-pushed the format_cfg_select branch from c267330 to d32c7e9Compare July 30, 2026 04:29

test: Add test case where cfg_select! falls back to default macro h…
ca398cd
…andling

jieyouxu approved these changes Jul 31, 2026
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rust-borsBot 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 Jul 31, 2026

jieyouxu added the F-cfg_select `#![feature(cfg_select)]` label Jul 31, 2026

JonathanBrouwer mentioned this pull request Jul 31, 2026
Rollup of 11 pull requests #160273
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Rollup of 17 pull requests #160278
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Rollup of 21 pull requests #160283
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Rollup of 22 pull requests #160284
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rust-borsBot merged commit 5ba5032 into rust-lang:mainJul 31, 2026
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ytmimi mentioned this pull request Aug 1, 2026
Formatting for cfg_select rust-lang/style-team#201
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jieyouxu added the relnotes Marks issues that should be documented in the release notes of the next release. label Aug 1, 2026

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Tracking issue for release notes of #154202: rustfmt: Format cfg_select!#160321
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SDM driver support esp-rs/esp-hal#5610
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chore: Run cargo +nightly fmt --all ruffle-rs/ruffle#24376
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subtree-push nightly-2026-08-11 rust-lang/rustfmt#7026
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rustfmt formatting of cfg_select! pending for Rust 1.99 diverges from style FCP #160944
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rustfmt: restrict cfg_select! formatting to the nightly release channel #160998
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Initial style team discussions

Follow-up: unbraced expressions are permitted

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