Make ExitStatus an inhabited type on all platforms

Even where actually running processes is not supported.
Needed for the next commit.

The manual trait implementations now belong on ExitStatusError,
which still can't exist.

Author: ijackson

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

@@ -99,58 +99,59 @@ impl fmt::Debug for Command {
     }
 }
 
-pub struct ExitStatus(!);
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[non_exhaustive]
+pub struct ExitStatus();
 
 impl ExitStatus {
     pub fn exit_ok(&self) -> Result<(), ExitStatusError> {
-        self.0
+        Ok(())
     }
 
     pub fn code(&self) -> Option<i32> {
-        self.0
+        Some(0)
     }
 }
 
-impl Clone for ExitStatus {
-    fn clone(&self) -> ExitStatus {
-        self.0
+impl fmt::Display for ExitStatus {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "<dummy exit status>")
     }
 }
 
-impl Copy for ExitStatus {}
+pub struct ExitStatusError(!);
 
-impl PartialEq for ExitStatus {
-    fn eq(&self, _other: &ExitStatus) -> bool {
+impl Clone for ExitStatusError {
+    fn clone(&self) -> ExitStatusError {
         self.0
     }
 }
 
-impl Eq for ExitStatus {}
+impl Copy for ExitStatusError {}
 
-impl fmt::Debug for ExitStatus {
-    fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl PartialEq for ExitStatusError {
+    fn eq(&self, _other: &ExitStatusError) -> bool {
         self.0
     }
 }
 
-impl fmt::Display for ExitStatus {
+impl Eq for ExitStatusError {}
+
+impl fmt::Debug for ExitStatusError {
     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.0
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
-pub struct ExitStatusError(ExitStatus);
-
 impl Into<ExitStatus> for ExitStatusError {
     fn into(self) -> ExitStatus {
-        self.0.0
+        self.0
     }
 }
 
 impl ExitStatusError {
     pub fn code(self) -> Option<NonZeroI32> {
-        self.0.0
+        self.0
     }
 }