From 1ae4a0cc3487f28b29f36afe8056535afad21e7b Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Sun, 10 Aug 2025 14:25:43 -0700
Subject: 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.
---
 library/std/src/sys/alloc/mod.rs  | 30 +++++++++++++++++++-----------
 library/std/src/sys/alloc/unix.rs | 10 ++++------
 2 files changed, 23 insertions(+), 17 deletions(-)

(limited to 'library/std/src/sys/alloc')

diff --git a/library/std/src/sys/alloc/mod.rs b/library/std/src/sys/alloc/mod.rs
index f3af1f7f599..6d4b09494a3 100644
--- a/library/std/src/sys/alloc/mod.rs
+++ b/library/std/src/sys/alloc/mod.rs
@@ -68,29 +68,37 @@ unsafe fn realloc_fallback(
     }
 }
 
-cfg_if::cfg_if! {
-    if #[cfg(any(
+cfg_select! {
+    any(
         target_family = "unix",
         target_os = "wasi",
         target_os = "teeos",
         target_os = "trusty",
-    ))] {
+    ) => {
         mod unix;
-    } else if #[cfg(target_os = "windows")] {
+    }
+    target_os = "windows" => {
         mod windows;
-    } else if #[cfg(target_os = "hermit")] {
+    }
+    target_os = "hermit" => {
         mod hermit;
-    } else if #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] {
+    }
+    all(target_vendor = "fortanix", target_env = "sgx") => {
         mod sgx;
-    } else if #[cfg(target_os = "solid_asp3")] {
+    }
+    target_os = "solid_asp3" => {
         mod solid;
-    } else if #[cfg(target_os = "uefi")] {
+    }
+    target_os = "uefi" => {
         mod uefi;
-    } else if #[cfg(target_family = "wasm")] {
+    }
+    target_family = "wasm" => {
         mod wasm;
-    } else if #[cfg(target_os = "xous")] {
+    }
+    target_os = "xous" => {
         mod xous;
-    } else if #[cfg(target_os = "zkvm")] {
+    }
+    target_os = "zkvm" => {
         mod zkvm;
     }
 }
diff --git a/library/std/src/sys/alloc/unix.rs b/library/std/src/sys/alloc/unix.rs
index a7ac4117ec9..3d369b08abc 100644
--- a/library/std/src/sys/alloc/unix.rs
+++ b/library/std/src/sys/alloc/unix.rs
@@ -58,18 +58,16 @@ unsafe impl GlobalAlloc for System {
     }
 }
 
-cfg_if::cfg_if! {
+cfg_select! {
     // We use posix_memalign wherever possible, but some targets have very incomplete POSIX coverage
     // so we need a fallback for those.
-    if #[cfg(any(
-        target_os = "horizon",
-        target_os = "vita",
-    ))] {
+    any(target_os = "horizon", target_os = "vita") => {
         #[inline]
         unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
             unsafe { libc::memalign(layout.align(), layout.size()) as *mut u8 }
         }
-    } else {
+    }
+    _ => {
         #[inline]
         #[cfg_attr(target_os = "vxworks", allow(unused_unsafe))]
         unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
-- 
cgit 1.4.1-3-g733a5