Fix suggestion on CallToDeprecatedSafeFnRequiresUnsafe diagnostic

compiler/rustc_mir_build/src/errors.rs

@@ -22,7 +22,7 @@ pub(crate) struct CallToDeprecatedSafeFnRequiresUnsafe {
 
 #[derive(Subdiagnostic)]
 #[multipart_suggestion(
-    "you can wrap the call in an `unsafe` block if you can guarantee that the environment access only happens in single-threaded code",
+    "you can wrap the call in an `unsafe` block if you can guarantee {$guarantee}",
     applicability = "machine-applicable"
 )]
 pub(crate) struct CallToDeprecatedSafeFnRequiresUnsafeSub {

tests/ui/rust-2024/unsafe-before_exec-suggestion.fixed

@@ -0,0 +1,18 @@
+//@ edition:2015
+//@ only-unix
+//@ run-rustfix
+
+#![deny(deprecated_safe_2024)]
+
+use std::process::Command;
+use std::os::unix::process::CommandExt;
+
+#[allow(deprecated)]
+fn main() {
+    let mut cmd = Command::new("sleep");
+    // TODO: Audit that the closure is async-signal-safe.
+    unsafe { cmd.before_exec(|| Ok(())) };
+    //~^ ERROR call to deprecated safe function
+    //~| WARN this is accepted in the current edition
+    drop(cmd);
+}

tests/ui/rust-2024/unsafe-before_exec-suggestion.rs

@@ -0,0 +1,17 @@
+//@ edition:2015
+//@ only-unix
+//@ run-rustfix
+
+#![deny(deprecated_safe_2024)]
+
+use std::process::Command;
+use std::os::unix::process::CommandExt;
+
+#[allow(deprecated)]
+fn main() {
+    let mut cmd = Command::new("sleep");
+    cmd.before_exec(|| Ok(()));
+    //~^ ERROR call to deprecated safe function
+    //~| WARN this is accepted in the current edition
+    drop(cmd);
+}

tests/ui/rust-2024/unsafe-before_exec-suggestion.stderr

@@ -0,0 +1,21 @@
+error: call to deprecated safe function `std::os::unix::process::CommandExt::before_exec` is unsafe and requires unsafe block
+  --> $DIR/unsafe-before_exec-suggestion.rs:13:5
+   |
+LL |     cmd.before_exec(|| Ok(()));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2024!
+   = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/newly-unsafe-functions.html>
+note: the lint level is defined here
+  --> $DIR/unsafe-before_exec-suggestion.rs:5:9
+   |
+LL | #![deny(deprecated_safe_2024)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+help: you can wrap the call in an `unsafe` block if you can guarantee that the closure is async-signal-safe
+   |
+LL +     // TODO: Audit that the closure is async-signal-safe.
+LL ~     unsafe { cmd.before_exec(|| Ok(())) };
+   |
+
+error: aborting due to 1 previous error
+