Auto merge of #82973 - ijackson:exitstatuserror, r=yaahc

Provide ExitStatusError

Closes #73125

In MR #81452 "Add #[must_use] to [...] process::ExitStatus" we concluded that the existing arrangements in are too awkward so adding that `#[must_use]` is blocked on improving the ergonomics.

I wrote a mini-RFC-style discusion of the approach in https://github.com/rust-lang/rust/issues/73125#issuecomment-771092741

1 files changed, 46 insertions, 7 deletions

diff --git a/library/std/src/os/unix/process.rs b/library/std/src/os/unix/process.rs
index f014a3d7b25..3dc389b7582 100644
--- a/library/std/src/os/unix/process.rs
+++ b/library/std/src/os/unix/process.rs
@@ -201,22 +201,32 @@ impl CommandExt for process::Command {
     }
 }
 
-/// Unix-specific extensions to [`process::ExitStatus`].
+/// Unix-specific extensions to [`process::ExitStatus`] and
+/// [`ExitStatusError`](process::ExitStatusError).
 ///
-/// On Unix, `ExitStatus` **does not necessarily represent an exit status**, as passed to the
-/// `exit` system call or returned by [`ExitStatus::code()`](crate::process::ExitStatus::code).
-/// It represents **any wait status**, as returned by one of the `wait` family of system calls.
+/// On Unix, `ExitStatus` **does not necessarily represent an exit status**, as
+/// passed to the `exit` system call or returned by
+/// [`ExitStatus::code()`](crate::process::ExitStatus::code).  It represents **any wait status**
+/// as returned by one of the `wait` family of system
+/// calls.
 ///
-/// This is because a Unix wait status (a Rust `ExitStatus`) can represent a Unix exit status, but
-/// can also represent other kinds of process event.
+/// A Unix wait status (a Rust `ExitStatus`) can represent a Unix exit status, but can also
+/// represent other kinds of process event.
 ///
 /// This trait is sealed: it cannot be implemented outside the standard library.
 /// This is so that future additional methods are not breaking changes.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ExitStatusExt: Sealed {
-    /// Creates a new `ExitStatus` from the raw underlying integer status value from `wait`
+    /// Creates a new `ExitStatus` or `ExitStatusError` from the raw underlying integer status
+    /// value from `wait`
     ///
     /// The value should be a **wait status, not an exit status**.
+    ///
+    /// # Panics
+    ///
+    /// Panics on an attempt to make an `ExitStatusError` from a wait status of `0`.
+    ///
+    /// Making an `ExitStatus` always succeds and never panics.
     #[stable(feature = "exit_status_from", since = "1.12.0")]
     fn from_raw(raw: i32) -> Self;
 
@@ -278,6 +288,35 @@ impl ExitStatusExt for process::ExitStatus {
     }
 }
 
+#[unstable(feature = "exit_status_error", issue = "84908")]
+impl ExitStatusExt for process::ExitStatusError {
+    fn from_raw(raw: i32) -> Self {
+        process::ExitStatus::from_raw(raw)
+            .exit_ok()
+            .expect_err("<ExitStatusError as ExitStatusExt>::from_raw(0) but zero is not an error")
+    }
+
+    fn signal(&self) -> Option<i32> {
+        self.into_status().signal()
+    }
+
+    fn core_dumped(&self) -> bool {
+        self.into_status().core_dumped()
+    }
+
+    fn stopped_signal(&self) -> Option<i32> {
+        self.into_status().stopped_signal()
+    }
+
+    fn continued(&self) -> bool {
+        self.into_status().continued()
+    }
+
+    fn into_raw(self) -> i32 {
+        self.into_status().into_raw()
+    }
+}
+
 #[stable(feature = "process_extensions", since = "1.2.0")]
 impl FromRawFd for process::Stdio {
     #[inline]