library: Migrate from `cfg_if` to `cfg_select` #145489

joshtriplett · 2025-08-16T10:55:08Z

Migrate the standard library from using the external cfg_if crate to using the now-built-in cfg_select macro.

This does not yet eliminate the dependency from library/std/Cargo.toml, because while the standard library itself no longer uses cfg_if, it also incorporates the backtrace crate, which does.

Migration assisted by the following vim command (after selecting the full cfg_if! invocation):

'<,'>s/\(cfg_if::\)\?cfg_if/cfg_select/ | '<,'>s/^\( *\)} else {/\1}\r\1_ => {/c | '<,'>s/^\( *\)} else if #\[cfg(\(.*\))\] /\1}\r\1\2 => /e | '<,'>s/if #\[cfg(\(.*\))\] {/\1 => {/e

This is imperfect, but substantially accelerated the process. This prompts for confirmation on the } else { since that can also appear inside one of the arms. This also requires manual intervention to handle any multi-line conditions.

rustbot · 2025-08-16T10:55:13Z

r? @Mark-Simulacrum

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Migrate the standard library from using the external `cfg_if` crate to using the now-built-in `cfg_select` macro. This does not yet eliminate the dependency from `library/std/Cargo.toml`, because while the standard library itself no longer uses `cfg_if`, it also incorporates the `backtrace` crate, which does. Migration assisted by the following vim command (after selecting the full `cfg_if!` invocation): ``` '<,'>s/\(cfg_if::\)\?cfg_if/cfg_select/ | '<,'>s/^\( *\)} else {/\1}\r\1_ => {/c | '<,'>s/^\( *\)} else if #\[cfg(\(.*\))\] /\1}\r\1\2 => /e | '<,'>s/if #\[cfg(\(.*\))\] {/\1 => {/e ``` This is imperfect, but substantially accelerated the process. This prompts for confirmation on the `} else {` since that can also appear inside one of the arms. This also requires manual intervention to handle any multi-line conditions.

joshtriplett · 2025-08-16T22:03:03Z

r? @Amanieu

Amanieu

r=me

library/unwind/src/libunwind.rs

The previous code inside `cfg_if!` wasn't indented, so the conversion to `cfg_select!` left it not indented. Indent it.

joshtriplett · 2025-08-17T06:30:20Z

@bors r=Amanieu p=1
(Prone to conflicts.)

bors · 2025-08-17T06:30:23Z

📌 Commit bc9725c has been approved by Amanieu

It is now in the queue for this repository.

library: Migrate from `cfg_if` to `cfg_select` Migrate the standard library from using the external `cfg_if` crate to using the now-built-in `cfg_select` macro. This does not yet eliminate the dependency from `library/std/Cargo.toml`, because while the standard library itself no longer uses `cfg_if`, it also incorporates the `backtrace` crate, which does. Migration assisted by the following vim command (after selecting the full `cfg_if!` invocation): ``` '<,'>s/\(cfg_if::\)\?cfg_if/cfg_select/ | '<,'>s/^\( *\)} else {/\1}\r\1_ => {/c | '<,'>s/^\( *\)} else if #\[cfg(\(.*\))\] /\1}\r\1\2 => /e | '<,'>s/if #\[cfg(\(.*\))\] {/\1 => {/e ``` This is imperfect, but substantially accelerated the process. This prompts for confirmation on the `} else {` since that can also appear inside one of the arms. This also requires manual intervention to handle any multi-line conditions.

Rollup of 10 pull requests Successful merges: - #144476 (rustdoc-search: search backend with partitioned suffix tree) - #144838 (Fix outdated doc comment) - #145206 (Port `#[custom_mir(..)]` to the new attribute system) - #145208 (Implement declarative (`macro_rules!`) derive macros (RFC 3698)) - #145420 (cg_llvm: Use LLVM-C bindings for `LLVMSetTailCallKind`, `LLVMGetTypeKind`) - #145451 (Add static glibc to the nix dev shell) - #145460 (Speedup `copy_src_dirs` in bootstrap) - #145476 (Fix typo in doc for library/std/src/fs.rs#set_permissions) - #145485 (Fix deprecation attributes on foreign statics) - #145489 (library: Migrate from `cfg_if` to `cfg_select`) r? `@ghost` `@rustbot` modify labels: rollup

Zalathar · 2025-08-17T09:07:09Z

Failed in rollup: #145521 (comment)

@bors r-
@bors try jobs=x86_64-gnu-llvm-19-3

library: Migrate from `cfg_if` to `cfg_select` try-job: x86_64-gnu-llvm-19-3

rust-bors · 2025-08-17T10:55:07Z

💔 Test for b3311ae failed: CI. Failed jobs:

try - x86_64-gnu-llvm-19-3 (web logs, extended logs)

joshtriplett · 2025-08-17T22:45:32Z

@bors r=Amanieu rollup=iffy p=1

bors · 2025-08-17T22:45:35Z

📌 Commit c44c1bb has been approved by Amanieu

It is now in the queue for this repository.

library: Migrate from `cfg_if` to `cfg_select` Migrate the standard library from using the external `cfg_if` crate to using the now-built-in `cfg_select` macro. This does not yet eliminate the dependency from `library/std/Cargo.toml`, because while the standard library itself no longer uses `cfg_if`, it also incorporates the `backtrace` crate, which does. Migration assisted by the following vim command (after selecting the full `cfg_if!` invocation): ``` '<,'>s/\(cfg_if::\)\?cfg_if/cfg_select/ | '<,'>s/^\( *\)} else {/\1}\r\1_ => {/c | '<,'>s/^\( *\)} else if #\[cfg(\(.*\))\] /\1}\r\1\2 => /e | '<,'>s/if #\[cfg(\(.*\))\] {/\1 => {/e ``` This is imperfect, but substantially accelerated the process. This prompts for confirmation on the `} else {` since that can also appear inside one of the arms. This also requires manual intervention to handle any multi-line conditions.

Rollup of 19 pull requests Successful merges: - #140956 (`impl PartialEq<{str,String}> for {Path,PathBuf}`) - #141744 (Stabilize `ip_from`) - #144804 (Don't warn on never to any `as` casts as unreachable) - #144983 (Rehome 37 `tests/ui/issues/` tests to other subdirectories under `tests/ui/`) - #145025 (run spellcheck as a tidy extra check in ci) - #145041 (rework GAT borrowck limitation error) - #145243 (take attr style into account in diagnostics) - #145359 (Fix bug where `rustdoc-js` tester would not pick the right `search.js` file if there is more than one) - #145429 (Couple of codegen_fn_attrs improvements) - #145452 (Do not strip binaries in bootstrap everytime if they are unchanged) - #145486 (Fix `unicode_data.rs` mention message) - #145489 (library: Migrate from `cfg_if` to `cfg_select`) - #145493 (remove `should_render` in `PrintAttribute` derive) - #145500 (Port must_use to the new target checking) - #145505 (Simplify span caches) - #145511 (Rust build fails on OpenBSD after using file_lock feature) - #145516 (Weekly `cargo update`) - #145533 (Reorder `lto` options from most to least optimizing) - #145550 (Avoid using `()` in `derive(From)` output.) r? `@ghost` `@rustbot` modify labels: rollup

library: Migrate from `cfg_if` to `cfg_select` Migrate the standard library from using the external `cfg_if` crate to using the now-built-in `cfg_select` macro. This does not yet eliminate the dependency from `library/std/Cargo.toml`, because while the standard library itself no longer uses `cfg_if`, it also incorporates the `backtrace` crate, which does. Migration assisted by the following vim command (after selecting the full `cfg_if!` invocation): ``` '<,'>s/\(cfg_if::\)\?cfg_if/cfg_select/ | '<,'>s/^\( *\)} else {/\1}\r\1_ => {/c | '<,'>s/^\( *\)} else if #\[cfg(\(.*\))\] /\1}\r\1\2 => /e | '<,'>s/if #\[cfg(\(.*\))\] {/\1 => {/e ``` This is imperfect, but substantially accelerated the process. This prompts for confirmation on the `} else {` since that can also appear inside one of the arms. This also requires manual intervention to handle any multi-line conditions.

bors · 2025-08-18T19:37:36Z

⌛ Testing commit c44c1bb with merge 9eb4a26...

joshtriplett added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Aug 16, 2025

rustbot assigned Mark-Simulacrum Aug 16, 2025

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joshtriplett force-pushed the cfg-if-not branch from bc7d167 to edeadb0 Compare August 16, 2025 10:58

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joshtriplett force-pushed the cfg-if-not branch from edeadb0 to 1ae4a0c Compare August 16, 2025 12:28

jieyouxu added the F-cfg_select `#![feature(cfg_select)]` label Aug 16, 2025

rustbot assigned Amanieu and unassigned Mark-Simulacrum Aug 16, 2025

Amanieu reviewed Aug 16, 2025

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Indent some code inside cfg_select!

bc9725c

The previous code inside `cfg_if!` wasn't indented, so the conversion to `cfg_select!` left it not indented. Indent it.

a4lg mentioned this pull request Aug 17, 2025

std_detect: RISC-V: implement implication to "C" #145415

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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 Aug 17, 2025

Zalathar mentioned this pull request Aug 17, 2025

Rollup of 10 pull requests #145521

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Auto merge of #145489 - joshtriplett:cfg-if-not, r=<try>

b3311ae

library: Migrate from `cfg_if` to `cfg_select` try-job: x86_64-gnu-llvm-19-3

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Fix up library crate order in linker test

c44c1bb

rustbot added the A-run-make Area: port run-make Makefiles to rmake.rs label Aug 17, 2025

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Zalathar mentioned this pull request Aug 18, 2025

Rollup of 19 pull requests #145552

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Rollup of 18 pull requests #145566

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library: Migrate from `cfg_if` to `cfg_select` #145489