system: add mkdir_unique_dir

Author: dra27

master_changes.md

@@ -214,3 +214,4 @@ users)
   * `OpamCompat`: add `Seq.find_map` from OCaml 4.14 [#6000 @dra27]
   * `OpamStd.Sys.{get_windows_executable_variant,get_cygwin_variant,is_cygwin_variant}`: renamed `~cygbin` to `?search_in_path` with a change in semantics so that it acts as though the directory was simply the first entry in PATH [#6000 @dra27]
   * `OpamConsole.Symbols`: add `collision` symbol [#5457 @dra27]
+  * `OpamSystem`: add `mk_unique_dir` that returns an unique directory name as `mk_temp_dir` but not in temporary directory [#5457 @dra27]

src/core/opamSystem.ml

@@ -88,6 +88,13 @@ let rec mk_temp_dir ?(prefix="opam") () =
   else
     real_path s
 
+let rec mk_unique_dir ~dir ?(prefix="opam") () =
+  let s = dir / Printf.sprintf "%s-%06x" prefix (Random.int 0xFFFFFF) in
+  if Sys.file_exists s then
+    mk_unique_dir ~dir ~prefix ()
+  else
+    real_path s
+
 let safe_mkdir dir =
   try
     log "mkdir %s" dir;

src/core/opamSystem.mli

@@ -51,6 +51,10 @@ val verbose_for_base_commands: unit -> bool
     (if [prefix] is not set), pid, and random number. *)
 val mk_temp_dir: ?prefix:string -> unit -> string
 
+(** Returns a directory name, in the [~dir], composed by {i opam}
+    (if [prefix] is not set), and a random number. *)
+val mk_unique_dir: dir:string -> ?prefix:string -> unit -> string
+
 (** [copy_file src dst] copies [src] to [dst]. Remove [dst] before the copy
     if it is a link. *)
 val copy_file: string -> string -> unit