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/env/mod.rs  | 31 ++++++++++++++++++++-----------
 library/std/src/sys/env/wasi.rs |  7 ++++---
 2 files changed, 24 insertions(+), 14 deletions(-)

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

diff --git a/library/std/src/sys/env/mod.rs b/library/std/src/sys/env/mod.rs
index d81ff875c83..f211a9fc86b 100644
--- a/library/std/src/sys/env/mod.rs
+++ b/library/std/src/sys/env/mod.rs
@@ -13,35 +13,44 @@
 ))]
 mod common;
 
-cfg_if::cfg_if! {
-    if #[cfg(target_family = "unix")] {
+cfg_select! {
+    target_family = "unix" => {
         mod unix;
         pub use unix::*;
-    } else if #[cfg(target_family = "windows")] {
+    }
+    target_family = "windows" => {
         mod windows;
         pub use windows::*;
-    } else if #[cfg(target_os = "hermit")] {
+    }
+    target_os = "hermit" => {
         mod hermit;
         pub use hermit::*;
-    } else if #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] {
+    }
+    all(target_vendor = "fortanix", target_env = "sgx") => {
         mod sgx;
         pub use sgx::*;
-    } else if #[cfg(target_os = "solid_asp3")] {
+    }
+    target_os = "solid_asp3" => {
         mod solid;
         pub use solid::*;
-    } else if #[cfg(target_os = "uefi")] {
+    }
+    target_os = "uefi" => {
         mod uefi;
         pub use uefi::*;
-    } else if #[cfg(target_os = "wasi")] {
+    }
+    target_os = "wasi" => {
         mod wasi;
         pub use wasi::*;
-    } else if #[cfg(target_os = "xous")] {
+    }
+    target_os = "xous" => {
         mod xous;
         pub use xous::*;
-    } else if #[cfg(target_os = "zkvm")] {
+    }
+    target_os = "zkvm" => {
         mod zkvm;
         pub use zkvm::*;
-    } else {
+    }
+    _ => {
         mod unsupported;
         pub use unsupported::*;
     }
diff --git a/library/std/src/sys/env/wasi.rs b/library/std/src/sys/env/wasi.rs
index 3719f9db51e..1327cbc3263 100644
--- a/library/std/src/sys/env/wasi.rs
+++ b/library/std/src/sys/env/wasi.rs
@@ -7,8 +7,8 @@ use crate::os::wasi::prelude::*;
 use crate::sys::common::small_c_string::run_with_cstr;
 use crate::sys::pal::os::{cvt, libc};
 
-cfg_if::cfg_if! {
-    if #[cfg(target_feature = "atomics")] {
+cfg_select! {
+    target_feature = "atomics" => {
         // Access to the environment must be protected by a lock in multi-threaded scenarios.
         use crate::sync::{PoisonError, RwLock};
         static ENV_LOCK: RwLock<()> = RwLock::new(());
@@ -18,7 +18,8 @@ cfg_if::cfg_if! {
         pub fn env_write_lock() -> impl Drop {
             ENV_LOCK.write().unwrap_or_else(PoisonError::into_inner)
         }
-    } else {
+    }
+    _ => {
         // No need for a lock if we are single-threaded.
         pub fn env_read_lock() -> impl Drop {
             Box::new(())
-- 
cgit 1.4.1-3-g733a5