Allow redirecting subprocess stdout to our stderr etc.

.github/workflows/ci.yml

@@ -58,6 +58,12 @@ jobs:
           - name: x86_64-gnu-llvm-14
             os: ubuntu-20.04-16core-64gb
             env: {}
+          - name: x86_64-msvc-1
+            env:
+              RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --enable-profiler"
+              SCRIPT: make ci-msvc
+            tidy: false
+            os: windows-2019-8core-32gb
           - name: x86_64-gnu-tools
             os: ubuntu-20.04-16core-64gb
             env: {}

library/std/src/process.rs

@@ -1491,6 +1491,66 @@ impl From<fs::File> for Stdio {
     }
 }
 
+#[stable(feature = "stdio_from_stdio", since = "CURRENT_RUSTC_VERSION")]
+impl From<io::Stdout> for Stdio {
+    /// Redirect command stdout/stderr to our stdout
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(exit_status_error)]
+    /// use std::io;
+    /// use std::process::Command;
+    ///
+    /// # fn test() -> Result<(), Box<dyn std::error::Error>> {
+    /// let output = Command::new("whoami")
+    // "whoami" is a command which exists on both Unix and Windows,
+    // and which succeeds, producing some stdout output but no stderr.
+    ///     .stdout(io::stdout())
+    ///     .output()?;
+    /// output.status.exit_ok()?;
+    /// assert!(output.stdout.is_empty());
+    /// # Ok(())
+    /// # }
+    /// #
+    /// # if cfg!(unix) {
+    /// #     test().unwrap();
+    /// # }
+    /// ```
+    fn from(inherit: io::Stdout) -> Stdio {
+        Stdio::from_inner(inherit.into())
+    }
+}
+
+#[stable(feature = "stdio_from_stdio", since = "CURRENT_RUSTC_VERSION")]
+impl From<io::Stderr> for Stdio {
+    /// Redirect command stdout/stderr to our stderr
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(exit_status_error)]
+    /// use std::io;
+    /// use std::process::Command;
+    ///
+    /// # fn test() -> Result<(), Box<dyn std::error::Error>> {
+    /// let output = Command::new("whoami")
+    ///     .stdout(io::stderr())
+    ///     .output()?;
+    /// output.status.exit_ok()?;
+    /// assert!(output.stdout.is_empty());
+    /// # Ok(())
+    /// # }
+    /// #
+    /// # if cfg!(unix) {
+    /// #     test().unwrap();
+    /// # }
+    /// ```
+    fn from(inherit: io::Stderr) -> Stdio {
+        Stdio::from_inner(inherit.into())
+    }
+}
+
 /// Describes the result of a process after it has terminated.
 ///
 /// This `struct` is used to represent the exit status or other termination of a child process.

library/std/src/sys/unix/process/process_common.rs

@@ -13,7 +13,7 @@ use crate::sys::fd::FileDesc;
 use crate::sys::fs::File;
 use crate::sys::pipe::{self, AnonPipe};
 use crate::sys_common::process::{CommandEnv, CommandEnvs};
-use crate::sys_common::IntoInner;
+use crate::sys_common::{FromInner, IntoInner};
 
 #[cfg(not(target_os = "fuchsia"))]
 use crate::sys::fs::OpenOptions;
@@ -150,6 +150,7 @@ pub enum Stdio {
     Null,
     MakePipe,
     Fd(FileDesc),
+    StaticFd(BorrowedFd<'static>),
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -463,6 +464,11 @@ impl Stdio {
                 }
             }
 
+            Stdio::StaticFd(fd) => {
+                let fd = FileDesc::from_inner(fd.try_clone_to_owned()?);
+                Ok((ChildStdio::Owned(fd), None))
+            }
+
             Stdio::MakePipe => {
                 let (reader, writer) = pipe::anon_pipe()?;
                 let (ours, theirs) = if readable { (writer, reader) } else { (reader, writer) };
@@ -497,6 +503,28 @@ impl From<File> for Stdio {
     }
 }
 
+impl From<io::Stdout> for Stdio {
+    fn from(_: io::Stdout) -> Stdio {
+        // This ought really to be is Stdio::StaticFd(input_argument.as_fd()).
+        // But AsFd::as_fd takes its argument by reference, and yields
+        // a bounded lifetime, so it's no use here. There is no AsStaticFd.
+        //
+        // Additionally AsFd is only implemented for the *locked* versions.
+        // We don't want to lock them here.  (The implications of not locking
+        // are the same as those for process::Stdio::inherit().)
+        //
+        // Arguably the hypothetical AsStaticFd and AsFd<'static>
+        // should be implemented for io::Stdout, not just for StdoutLocked.
+        Stdio::StaticFd(unsafe { BorrowedFd::borrow_raw(libc::STDOUT_FILENO) })
+    }
+}
+
+impl From<io::Stderr> for Stdio {
+    fn from(_: io::Stderr) -> Stdio {
+        Stdio::StaticFd(unsafe { BorrowedFd::borrow_raw(libc::STDERR_FILENO) })
+    }
+}
+
 impl ChildStdio {
     pub fn fd(&self) -> Option<c_int> {
         match *self {

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

@@ -170,6 +170,7 @@ pub struct Command {
 
 pub enum Stdio {
     Inherit,
+    InheritSpecific { from_stdio_id: c::DWORD },
     Null,
     MakePipe,
     Pipe(AnonPipe),
@@ -521,17 +522,19 @@ fn program_exists(path: &Path) -> Option<Vec<u16>> {
 
 impl Stdio {
     fn to_handle(&self, stdio_id: c::DWORD, pipe: &mut Option<AnonPipe>) -> io::Result<Handle> {
-        match *self {
-            Stdio::Inherit => match stdio::get_handle(stdio_id) {
-                Ok(io) => unsafe {
-                    let io = Handle::from_raw_handle(io);
-                    let ret = io.duplicate(0, true, c::DUPLICATE_SAME_ACCESS);
-                    io.into_raw_handle();
-                    ret
-                },
-                // If no stdio handle is available, then propagate the null value.
-                Err(..) => unsafe { Ok(Handle::from_raw_handle(ptr::null_mut())) },
+        let use_stdio_id = |stdio_id| match stdio::get_handle(stdio_id) {
+            Ok(io) => unsafe {
+                let io = Handle::from_raw_handle(io);
+                let ret = io.duplicate(0, true, c::DUPLICATE_SAME_ACCESS);
+                io.into_raw_handle();
+                ret
             },
+            // If no stdio handle is available, then propagate the null value.
+            Err(..) => unsafe { Ok(Handle::from_raw_handle(ptr::null_mut())) },
+        };
+        match *self {
+            Stdio::Inherit => use_stdio_id(stdio_id),
+            Stdio::InheritSpecific { from_stdio_id } => use_stdio_id(from_stdio_id),
 
             Stdio::MakePipe => {
                 let ours_readable = stdio_id != c::STD_INPUT_HANDLE;
@@ -579,6 +582,18 @@ impl From<File> for Stdio {
     }
 }
 
+impl From<io::Stdout> for Stdio {
+    fn from(_: io::Stdout) -> Stdio {
+        Stdio::InheritSpecific { from_stdio_id: c::STD_OUTPUT_HANDLE }
+    }
+}
+
+impl From<io::Stderr> for Stdio {
+    fn from(_: io::Stderr) -> Stdio {
+        Stdio::InheritSpecific { from_stdio_id: c::STD_ERROR_HANDLE }
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Processes
 ////////////////////////////////////////////////////////////////////////////////

src/ci/github-actions/ci.yml

@@ -326,6 +326,13 @@ jobs:
           - name: x86_64-gnu-llvm-14
             <<: *job-linux-16c
 
+          - name: x86_64-msvc-1
+            env:
+              RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-msvc --enable-profiler
+              SCRIPT: make ci-msvc
+            <<: *job-windows-8c
+            tidy: false
+
           - name: x86_64-gnu-tools
             <<: *job-linux-16c