Implement ExitCodeExt for Windows

library/std/src/os/windows/process.rs

@@ -194,3 +194,26 @@ impl ChildExt for process::Child {
         self.handle.main_thread_handle()
     }
 }
+
+/// Windows-specific extensions to [`process::ExitCode`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
+#[unstable(feature = "windows_process_exit_code_from", issue = "none")]
+pub trait ExitCodeExt: Sealed {
+    /// Creates a new `ExitCode` from the raw underlying `u32` return value of
+    /// a process.
+    ///
+    /// The exit code should not be 259, as this conflicts with the `STILL_ACTIVE`
+    /// macro returned from the `GetExitCodeProcess` function to signal that the
+    /// process has yet to run to completion.
+    #[unstable(feature = "windows_process_exit_code_from", issue = "none")]
+    fn from_raw(raw: u32) -> Self;
+}
+
+#[unstable(feature = "windows_process_exit_code_from", issue = "none")]
+impl ExitCodeExt for process::ExitCode {
+    fn from_raw(raw: u32) -> Self {
+        process::ExitCode::from_inner(From::from(raw))
+    }
+}

library/std/src/process.rs

@@ -1708,6 +1708,10 @@ impl crate::error::Error for ExitStatusError {}
 #[stable(feature = "process_exitcode", since = "1.61.0")]
 pub struct ExitCode(imp::ExitCode);
 
+/// Allows extension traits within `std`.
+#[unstable(feature = "sealed", issue = "none")]
+impl crate::sealed::Sealed for ExitCode {}
+
 #[stable(feature = "process_exitcode", since = "1.61.0")]
 impl ExitCode {
     /// The canonical `ExitCode` for successful termination on this platform.
@@ -1798,6 +1802,18 @@ impl From<u8> for ExitCode {
     }
 }
 
+impl AsInner<imp::ExitCode> for ExitCode {
+    fn as_inner(&self) -> &imp::ExitCode {
+        &self.0
+    }
+}
+
+impl FromInner<imp::ExitCode> for ExitCode {
+    fn from_inner(s: imp::ExitCode) -> ExitCode {
+        ExitCode(s)
+    }
+}
+
 impl Child {
     /// Forces the child process to exit. If the child has already exited, an [`InvalidInput`]
     /// error is returned.

library/std/src/sys/windows/process.rs

@@ -707,6 +707,12 @@ impl From<u8> for ExitCode {
     }
 }
 
+impl From<u32> for ExitCode {
+    fn from(code: u32) -> Self {
+        ExitCode(c::DWORD::from(code))
+    }
+}
+
 fn zeroed_startupinfo() -> c::STARTUPINFO {
     c::STARTUPINFO {
         cb: 0,