std: Allow creating ExitStatus from raw values

Sometimes a process may be waited on externally from the standard library, in
which case it can be useful to create a raw `ExitStatus` structure to return.
This commit extends the existing Unix `ExitStatusExt` extension trait and adds a
new Windows-specific `ExitStatusExt` extension trait to do this. The methods are
currently called `ExitStatus::from_raw`.

cc #32713

src/libstd/process.rs

@@ -459,6 +459,12 @@ impl AsInner<imp::ExitStatus> for ExitStatus {
     fn as_inner(&self) -> &imp::ExitStatus { &self.0 }
 }
 
+impl FromInner<imp::ExitStatus> for ExitStatus {
+    fn from_inner(s: imp::ExitStatus) -> ExitStatus {
+        ExitStatus(s)
+    }
+}
+
 #[stable(feature = "process", since = "1.0.0")]
 impl fmt::Display for ExitStatus {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

src/libstd/sys/unix/ext/process.rs

@@ -132,13 +132,22 @@ impl CommandExt for process::Command {
 /// Unix-specific extensions to `std::process::ExitStatus`
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ExitStatusExt {
+    /// Creates a new `ExitStatus` from the raw underlying `i32` return value of
+    /// a process.
+    #[unstable(feature = "exit_status_from", issue = "32713")]
+    fn from_raw(raw: i32) -> Self;
+
     /// If the process was terminated by a signal, returns that signal.
     #[stable(feature = "rust1", since = "1.0.0")]
     fn signal(&self) -> Option<i32>;
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ExitStatusExt for process::ExitStatus {
+    fn from_raw(raw: i32) -> Self {
+        process::ExitStatus::from_inner(From::from(raw))
+    }
+
     fn signal(&self) -> Option<i32> {
         self.as_inner().signal()
     }

src/libstd/sys/unix/process.rs

@@ -550,6 +550,12 @@ impl ExitStatus {
     }
 }
 
+impl From<c_int> for ExitStatus {
+    fn from(a: c_int) -> ExitStatus {
+        ExitStatus(a)
+    }
+}
+
 impl fmt::Display for ExitStatus {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         if let Some(code) = self.code() {

src/libstd/sys/windows/ext/process.rs

@@ -81,3 +81,18 @@ impl IntoRawHandle for process::ChildStderr {
         self.into_inner().into_handle().into_raw() as *mut _
     }
 }
+
+/// Windows-specific extensions to `std::process::ExitStatus`
+#[unstable(feature = "exit_status_from", issue = "32713")]
+pub trait ExitStatusExt {
+    /// Creates a new `ExitStatus` from the raw underlying `u32` return value of
+    /// a process.
+    fn from_raw(raw: u32) -> Self;
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl ExitStatusExt for process::ExitStatus {
+    fn from_raw(raw: u32) -> Self {
+        process::ExitStatus::from_inner(From::from(raw))
+    }
+}

src/libstd/sys/windows/process.rs

@@ -337,6 +337,12 @@ impl ExitStatus {
     }
 }
 
+impl From<c::DWORD> for ExitStatus {
+    fn from(u: c::DWORD) -> ExitStatus {
+        ExitStatus(u)
+    }
+}
+
 impl fmt::Display for ExitStatus {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "exit code: {}", self.0)