std: Implement lowering and raising for process IO

This commit implements a number of standard traits for the standard library's
process I/O handles. The `FromRaw{Fd,Handle}` traits are now implemented for the
`Stdio` type and the `AsRaw{Fd,Handle}` traits are now implemented for the
`Child{Stdout,Stdin,Stderr}` types. Additionally this implements the
`AsRawHandle` trait for `Child` on Windows.

The stability markers for these implementations mention that they are stable for
1.1 as I will nominate this commit for cherry-picking to beta.

1 files changed, 48 insertions, 1 deletions

diff --git a/src/libstd/sys/unix/ext/process.rs b/src/libstd/sys/unix/ext/process.rs
index 45d0d62a015..2d30b016a2d 100644
--- a/src/libstd/sys/unix/ext/process.rs
+++ b/src/libstd/sys/unix/ext/process.rs
@@ -13,10 +13,11 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use os::unix::raw::{uid_t, gid_t};
+use os::unix::io::{FromRawFd, RawFd, AsRawFd};
 use prelude::v1::*;
 use process;
 use sys;
-use sys_common::{AsInnerMut, AsInner};
+use sys_common::{AsInnerMut, AsInner, FromInner};
 
 /// Unix-specific extensions to the `std::process::Command` builder
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -63,3 +64,49 @@ impl ExitStatusExt for process::ExitStatus {
         }
     }
 }
+
+#[stable(feature = "from_raw_os", since = "1.1.0")]
+impl FromRawFd for process::Stdio {
+    /// Creates a new instance of `Stdio` from the raw underlying file
+    /// descriptor.
+    ///
+    /// When this `Stdio` is used as an I/O handle for a child process the given
+    /// file descriptor will be `dup`d into the destination file descriptor in
+    /// the child process.
+    ///
+    /// Note that this function **does not** take ownership of the file
+    /// descriptor provided and it will **not** be closed when `Stdio` goes out
+    /// of scope. As a result this method is unsafe because due to the lack of
+    /// knowledge about the lifetime of the provided file descriptor, this could
+    /// cause another I/O primitive's ownership property of its file descriptor
+    /// to be violated.
+    ///
+    /// Also note that this file descriptor may be used multiple times to spawn
+    /// processes. For example the `Command::spawn` function could be called
+    /// more than once to spawn more than one process sharing this file
+    /// descriptor.
+    unsafe fn from_raw_fd(fd: RawFd) -> process::Stdio {
+        process::Stdio::from_inner(sys::process::Stdio::Fd(fd))
+    }
+}
+
+#[stable(feature = "from_raw_os", since = "1.1.0")]
+impl AsRawFd for process::ChildStdin {
+    fn as_raw_fd(&self) -> RawFd {
+        self.as_inner().fd().raw()
+    }
+}
+
+#[stable(feature = "from_raw_os", since = "1.1.0")]
+impl AsRawFd for process::ChildStdout {
+    fn as_raw_fd(&self) -> RawFd {
+        self.as_inner().fd().raw()
+    }
+}
+
+#[stable(feature = "from_raw_os", since = "1.1.0")]
+impl AsRawFd for process::ChildStderr {
+    fn as_raw_fd(&self) -> RawFd {
+        self.as_inner().fd().raw()
+    }
+}