From 5ae03863ded632b6cedeed29cc53e9c69fe5b56b Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Tue, 4 Jun 2024 11:50:18 +0200
Subject: [PATCH] CommandExt::before_exec: deprecate safety in edition 2024

---
 library/std/src/os/unix/process.rs              | 14 +++++++++++---
 .../rust-2024/unsafe-before_exec.e2024.stderr   | 11 +++++++++++
 tests/ui/rust-2024/unsafe-before_exec.rs        | 17 +++++++++++++++++
 3 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 tests/ui/rust-2024/unsafe-before_exec.e2024.stderr
 create mode 100644 tests/ui/rust-2024/unsafe-before_exec.rs

diff --git a/library/std/src/os/unix/process.rs b/library/std/src/os/unix/process.rs
index c53423675bd00..46202441d4e38 100644
--- a/library/std/src/os/unix/process.rs
+++ b/library/std/src/os/unix/process.rs
@@ -109,13 +109,21 @@ pub trait CommandExt: Sealed {
     /// Schedules a closure to be run just before the `exec` function is
     /// invoked.
     ///
-    /// This method is stable and usable, but it should be unsafe. To fix
-    /// that, it got deprecated in favor of the unsafe [`pre_exec`].
+    /// `before_exec` used to be a safe method, but it needs to be unsafe since the closure may only
+    /// perform operations that are *async-signal-safe*. Hence it got deprecated in favor of the
+    /// unsafe [`pre_exec`]. Meanwhile, Rust gained the ability to make an existing safe method
+    /// fully unsafe in a new edition, which is how `before_exec` became `unsafe`. It still also
+    /// remains deprecated; `pre_exec` should be used instead.
     ///
     /// [`pre_exec`]: CommandExt::pre_exec
     #[stable(feature = "process_exec", since = "1.15.0")]
     #[deprecated(since = "1.37.0", note = "should be unsafe, use `pre_exec` instead")]
-    fn before_exec<F>(&mut self, f: F) -> &mut process::Command
+    #[cfg_attr(bootstrap, rustc_deprecated_safe_2024)]
+    #[cfg_attr(
+        not(bootstrap),
+        rustc_deprecated_safe_2024(audit_that = "the closure is async-signal-safe")
+    )]
+    unsafe fn before_exec<F>(&mut self, f: F) -> &mut process::Command
     where
         F: FnMut() -> io::Result<()> + Send + Sync + 'static,
     {
diff --git a/tests/ui/rust-2024/unsafe-before_exec.e2024.stderr b/tests/ui/rust-2024/unsafe-before_exec.e2024.stderr
new file mode 100644
index 0000000000000..2798ccdefd0c6
--- /dev/null
+++ b/tests/ui/rust-2024/unsafe-before_exec.e2024.stderr
@@ -0,0 +1,11 @@
+error[E0133]: call to unsafe function `before_exec` is unsafe and requires unsafe block
+  --> $DIR/unsafe-before_exec.rs:14:5
+   |
+LL |     cmd.before_exec(|| Ok(()));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0133`.
diff --git a/tests/ui/rust-2024/unsafe-before_exec.rs b/tests/ui/rust-2024/unsafe-before_exec.rs
new file mode 100644
index 0000000000000..540394da80ef8
--- /dev/null
+++ b/tests/ui/rust-2024/unsafe-before_exec.rs
@@ -0,0 +1,17 @@
+//@ revisions: e2021 e2024
+//@ only-unix
+//@[e2021] edition: 2021
+//@[e2021] check-pass
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+
+use std::process::Command;
+use std::os::unix::process::CommandExt;
+
+#[allow(deprecated)]
+fn main() {
+    let mut cmd = Command::new("sleep");
+    cmd.before_exec(|| Ok(()));
+    //[e2024]~^ ERROR call to unsafe function `before_exec` is unsafe
+    drop(cmd); // we don't actually run the command.
+}