From f1c4c6a1c198f83079092f9026823689823c55d4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20Ojeda=20B=C3=A4r?= <n.oje.bar@gmail.com>
Date: Mon, 23 Sep 2019 18:29:12 +0200
Subject: [PATCH 1/3] Add Filename.null

---
 stdlib/filename.ml  | 4 ++++
 stdlib/filename.mli | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/stdlib/filename.ml b/stdlib/filename.ml
index 2ac74a954..b0dd5c219 100644
--- a/stdlib/filename.ml
+++ b/stdlib/filename.ml
@@ -70,6 +70,7 @@ let generic_dirname is_dir_sep current_dir_name name =
   else trailing_sep (String.length name - 1)
 
 module type SYSDEPS = sig
+  val null : string
   val current_dir_name : string
   val parent_dir_name : string
   val dir_sep : string
@@ -88,6 +89,7 @@ module type SYSDEPS = sig
 end
 
 module Unix : SYSDEPS = struct
+  let null = "/dev/null"
   let current_dir_name = "."
   let parent_dir_name = ".."
   let dir_sep = "/"
@@ -128,6 +130,7 @@ module Unix : SYSDEPS = struct
 end
 
 module Win32 : SYSDEPS = struct
+  let null = "NUL"
   let current_dir_name = "."
   let parent_dir_name = ".."
   let dir_sep = "\\"
@@ -261,6 +264,7 @@ Quoting commands for execution by cmd.exe is difficult.
 end
 
 module Cygwin : SYSDEPS = struct
+  let null = "/dev/null"
   let current_dir_name = "."
   let parent_dir_name = ".."
   let dir_sep = "/"
diff --git a/stdlib/filename.mli b/stdlib/filename.mli
index 052301931..9e032b862 100644
--- a/stdlib/filename.mli
+++ b/stdlib/filename.mli
@@ -118,6 +118,10 @@ val dirname : string -> string
    This function conforms to the specification of POSIX.1-2008 for the
    [dirname] utility. *)
 
+val null : string
+(** [null] is ["/dev/null"] on POSIX and ["NUL"] on Windows. It represents a
+    file on the OS that discards all writes and returns end of file on reads. *)
+
 val temp_file : ?temp_dir: string -> string -> string -> string
 (** [temp_file prefix suffix] returns the name of a
    fresh temporary file in the temporary directory.

From e606e49b1619684c71d416fd8052cc8b02c5f48e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20Ojeda=20B=C3=A4r?= <n.oje.bar@gmail.com>
Date: Mon, 23 Sep 2019 18:30:56 +0200
Subject: [PATCH 2/3] Add test

---
 testsuite/tests/lib-filename/null.ml           | 8 ++++++++
 testsuite/tests/lib-unix/common/process_pid.ml | 8 +-------
 2 files changed, 9 insertions(+), 7 deletions(-)
 create mode 100644 testsuite/tests/lib-filename/null.ml

diff --git a/testsuite/tests/lib-filename/null.ml b/testsuite/tests/lib-filename/null.ml
new file mode 100644
index 000000000..048e36622
--- /dev/null
+++ b/testsuite/tests/lib-filename/null.ml
@@ -0,0 +1,8 @@
+(* TEST
+*)
+
+let () =
+  let ic = open_in Filename.null in
+  match input_char ic with
+  | exception End_of_file -> close_in ic
+  | _ -> assert false
diff --git a/testsuite/tests/lib-unix/common/process_pid.ml b/testsuite/tests/lib-unix/common/process_pid.ml
index 6df536bf2..8d8852f6d 100644
--- a/testsuite/tests/lib-unix/common/process_pid.ml
+++ b/testsuite/tests/lib-unix/common/process_pid.ml
@@ -5,17 +5,11 @@ include unix
 ** native
 *)
 
-let null =
-  if Sys.win32 then
-    "NUL"
-  else
-    "/dev/null"
-
 let () =
   let ic, _ as process =
     (* Redirect to null to avoid
        "The process tried to write to a nonexistent pipe." on Windows *)
-    Printf.ksprintf Unix.open_process "echo toto > %s" null
+    Printf.ksprintf Unix.open_process "echo toto > %s" Filename.null
   in
   assert
     (Unix.process_pid process = Unix.process_pid process);

From 91407069a436ff737fd8ada3c0638297816cf11d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20Ojeda=20B=C3=A4r?= <n.oje.bar@gmail.com>
Date: Mon, 23 Sep 2019 18:35:06 +0200
Subject: [PATCH 3/3] Changes

---
 Changes | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Changes b/Changes
index d167598fb..63581d0cb 100644
--- a/Changes
+++ b/Changes
@@ -195,6 +195,9 @@ Working version
   (Guillaume Munch-Maccagnoni, review by David Allsopp, Damien Doligez and
    Gabriel Scherer)
 
+- #8971: Add `Filename.null`, the conventional name of the "null" device.
+  (Nicolás Ojeda Bär, review by Xavier Leroy and Alain Frisch)
+
 ### Other libraries:
 
 - #1939, #2023: Implement Unix.truncate and Unix.ftruncate on Windows.