Use cfg_match! in core

[CAD97]

All of these uses of cfg_if! do not utilize that cfg_if! works with auto-doc(cfg), so no functionality is lost from switching to use cfg_match! instead. We do lose what rustfmt special support exists for cfg_if!, though.

Tracking issue: #115585

[rustbot]

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[Copilot]

Pull Request Overview

This PR updates the core library to use cfg_match! instead of cfg_if! to take advantage of the auto‑doc(cfg) capability.

• Replace occurrences of cfg_if! with cfg_match! in multiple sorting modules and FFI definitions.
• Remove the redundant cfg_if! macro in internal_macros.rs and enable the new cfg_match feature in lib.rs.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
library/core/src/slice/sort/stable/mod.rs	Updated conditional compilation to use cfg_match! in stable sort logic.
library/core/src/slice/sort/select.rs	Replaced cfg_if! with cfg_match! for improved pivot selection handling.
library/core/src/slice/sort/unstable/quicksort.rs	Swapped cfg_if! for cfg_match! in quicksort partitioning routines.
library/core/src/ffi/primitives.rs	Migrated FFI type definitions from cfg_if! to cfg_match! to align with new standards.
library/core/src/slice/sort/unstable/mod.rs	Updated unstable sort algorithms to use cfg_match! for conditional branches.
library/core/src/num/f32.rs	Changed f32 midpoint calculation to use cfg_match! for performance optimizations.
library/core/src/internal_macros.rs	Removed the legacy cfg_if! macro implementation.
library/core/src/lib.rs	Added the cfg_match feature flag to enable new conditional compilation support.

[CAD97]

Well, I wanted to see how well that worked, and no, that's wrong. Uses of cfg_match! aren't visible to feature(doc_autocfg), and none of the few exported definitions covered here document a required cfg. Certain versions of cfg_if! do propagate the cfg to individual items, in order to work somewhat better with doc autocfg, but core's version didn't anyway.

Probably won't be clicking that button ever again.

[joboet]

Great, thank you!
r? joboet
@bors r+ rollup=never p=1
(bumping this because it's quite likely to bitrot)

[bors]

📌 Commit 2e5a76c has been approved by joboet

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2e5a76c with merge 1644cb0...

[bors]

☀️ Test successful - checks-actions
Approved by: joboet
Pushing 1644cb0 to master...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing a2e6356 (parent) -> 1644cb0 (this PR)

Test differences

Show 58 test diffs

Additionally, 58 doctest diffs were found. These are ignored, as they are noisy.

Job group index

[rust-timer]

Finished benchmarking commit (1644cb0): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 3.0%, secondary 2.6%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.0%	[0.9%, 3.9%]	5
Regressions ❌ (secondary)	2.7%	[0.7%, 3.9%]	45
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	3.0%	[0.9%, 3.9%]	5

Cycles

Results (primary -2.3%, secondary 2.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.2%	[1.5%, 2.6%]	9
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 778.152s -> 777.476s (-0.09%)
Artifact size: 365.74 MiB -> 365.76 MiB (0.00%)