Consistently present absent stdio handles on Windows as NULL handles.

This addresses #90964 by making the std API consistent about presenting
absent stdio handles on Windows as NULL handles. Stdio handles may be
absent due to `#![windows_subsystem = "windows"]`, due to the console
being detached, or due to a child process having been launched from a
parent where stdio handles are absent.

Specifically, this fixes the case of child processes of parents with absent
stdio, which previously ended up with `stdin().as_raw_handle()` returning
`INVALID_HANDLE_VALUE`, which was surprising, and which overlapped with an
unrelated valid handle value. With this patch, `stdin().as_raw_handle()`
now returns null in these situation, which is consistent with what it
does in the parent process.

And, document this in the "Windows Portability Considerations" sections of
the relevant documentation.

1 files changed, 13 insertions, 0 deletions

diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index fafd1412d4c..ec53c46cd7b 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -309,6 +309,19 @@ impl Command {
         si.hStdOutput = stdout.as_raw_handle();
         si.hStdError = stderr.as_raw_handle();
 
+        // `CreateProcessW` fails with `ERROR_FILE_NOT_FOUND` if any of the
+        // stdio handles are null, so if we have null handles, set them to
+        // `INVALID_HANDLE_VALUE`.
+        if si.hStdInput.is_null() {
+            si.hStdInput = c::INVALID_HANDLE_VALUE;
+        }
+        if si.hStdOutput.is_null() {
+            si.hStdOutput = c::INVALID_HANDLE_VALUE;
+        }
+        if si.hStdError.is_null() {
+            si.hStdError = c::INVALID_HANDLE_VALUE;
+        }
+
         let program = to_u16s(&program)?;
         unsafe {
             cvt(c::CreateProcessW(