From ec36c97b3f6a5922dbf124c31065a1b067f500ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Antonin=20D=C3=A9cimo?= <antonin@tarides.com>
Date: Tue, 30 Nov 2021 18:16:43 +0100
Subject: [PATCH] Fix win32_spawn leaking dev_null fd in the parent process

---
 CHANGES                 |  6 ++++++
 src/unix/lwt_process.ml | 14 ++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/CHANGES b/CHANGES
index 2a08836ac9..0932632c27 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,9 @@
+===== dev =====
+
+====== Fixes ======
+
+  * Fix win32_spawn leaking dev_null fd in the parent process. (#906, Antonin Décimo)
+
 ===== 5.5.0 =====
 
 ====== Deprecations ======
diff --git a/src/unix/lwt_process.ml b/src/unix/lwt_process.ml
index cbd2a6e285..f6534938da 100644
--- a/src/unix/lwt_process.ml
+++ b/src/unix/lwt_process.ml
@@ -91,15 +91,21 @@ let win32_spawn
       (if prog = "" then None else Some prog) cmdline env cwd
       (stdin_fd, stdout_fd, stderr_fd)
   in
-  let close = function
+  let close fd fd' =
+    match fd with
     | `FD_move fd ->
       Unix.close fd
+    | `Dev_null ->
+      begin match fd' with
+        | Some fd' -> Unix.close fd'
+        | None -> assert false
+      end
     | _ ->
       ()
   in
-  close stdin;
-  close stdout;
-  close stderr;
+  close stdin stdin_fd;
+  close stdout stdout_fd;
+  close stderr stderr_fd;
   proc
 
 external win32_wait_job : Unix.file_descr -> int Lwt_unix.job =