Merge pull request #8971 from nojb/filename_nul

Add Filename.null

Changes

@@ -198,6 +198,9 @@ 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.

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 = "/"

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.

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

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);