Move path operations to backends

lib_eio/fs.ml

@@ -50,6 +50,15 @@ type 'a dir = ([> dir_ty] as 'a) r
 (** {2 Provider Interface} *)
 
 module Pi = struct
+
+  module type PATH = sig
+    val split : path -> (path * string) option
+    (** The implementation of {!Path.split}. *)
+
+    val join : path -> path -> path
+    (** The implementation of {!Path.(/)}. *)
+  end
+
   module type DIR = sig
     type t
 
@@ -76,6 +85,8 @@ module Pi = struct
     val chown : follow:bool -> ?uid:int64 -> ?gid:int64 -> t -> path -> unit
     val pp : t Fmt.t
     val native : t -> string -> string option
+
+    include PATH
   end
 
   type (_, _, _) Resource.pi +=

lib_eio/path.ml

@@ -1,22 +1,9 @@
 type 'a t = 'a Fs.dir * Fs.path
 
-(* Like [Filename.is_relative] but always using "/" as the separator. *)
-let is_relative = function
-  | "" -> true
-  | x -> x.[0] <> '/'
-
-(* Like [Filename.concat] but always using "/" as the separator. *)
-let concat a b =
-  let l = String.length a in
-  if l = 0 || a.[l - 1] = '/' then a ^ b
-  else a ^ "/" ^ b
-
-let ( / ) (dir, p1) p2 =
-  match p1, p2 with
-  | p1, "" -> (dir, concat p1 p2)
-  | _, p2 when not (is_relative p2) -> (dir, p2)
-  | ".", p2 -> (dir, p2)
-  | p1, p2 -> (dir, concat p1 p2)
+let ( / ) (d, p1) p2 =
+  let (Resource.T (_, ops)) = d in
+  let module X = (val (Resource.get ops Fs.Pi.Dir)) in
+  (d, X.join p1 p2)
 
 let pp f (Resource.T (t, ops), p) =
   let module X = (val (Resource.get ops Fs.Pi.Dir)) in
@@ -32,37 +19,10 @@ let native_exn t =
   | Some p -> p
   | None -> raise (Fs.err (Not_native (Fmt.str "%a" pp t)))
 
-(* Drop the first [n] characters from [s]. *)
-let string_drop s n =
-  String.sub s n (String.length s - n)
-
-(* "/foo/bar//" -> "/foo/bar"
-   "///" -> "/"
-   "foo/bar" -> "foo/bar"
- *)
-let remove_trailing_slashes s =
-  let rec aux i =
-    if i <= 1 || s.[i - 1] <> '/' then (
-      if i = String.length s then s
-      else String.sub s 0 i
-    ) else aux (i - 1)
-  in
-  aux (String.length s)
-
-let split (dir, p) =
-  match remove_trailing_slashes p with
-  | "" -> None
-  | "/" -> None
-  | p ->
-    match String.rindex_opt p '/' with
-    | None -> Some ((dir, ""), p)
-    | Some idx ->
-      let basename = string_drop p (idx + 1) in
-      let dirname =
-        if idx = 0 then "/"
-        else remove_trailing_slashes (String.sub p 0 idx)
-      in
-      Some ((dir, dirname), basename)
+let split (d, p) =
+  let (Resource.T (_, ops)) = d in
+  let module X = (val (Resource.get ops Fs.Pi.Dir)) in
+  X.split p |> Option.map (fun (dirname, basename) -> ((d, dirname), basename))
 
 let open_in ~sw t =
   let (Resource.T (dir, ops), path) = t in

lib_eio/path.mli

@@ -36,7 +36,10 @@ type 'a t = 'a Fs.dir * path
 
 val ( / ) : 'a t -> string -> 'a t
 (** [t / step] is [t] with [step] appended to [t]'s path,
-    or replacing [t]'s path if [step] is absolute:
+    or replacing [t]'s path if [step] stands alone
+    (for example, if it is absolute).
+
+    For POSIX systems (e.g. Linux and macOS), it will behave like this:
 
     - [(fd, "foo") / "bar" = (fd, "foo/bar")]
     - [(fd, "foo") / "/bar" = (fd, "/bar")] *)
@@ -69,7 +72,7 @@ val split : 'a t -> ('a t * string) option
 
     [split t = None] if there is nothing to split.
 
-    For example:
+    For POSIX systems (e.g. Linux and macOS), it will behave like this:
 
     - [split (root, "foo/bar") = Some ((root, "foo"), "bar")]
     - [split (root, "/foo/bar") = Some ((root, "/foo"), "bar")]

lib_eio/utils/eio_utils.ml

@@ -6,3 +6,4 @@ module Lf_queue = Lf_queue
 module Suspended = Suspended
 module Zzz = Zzz
 module Dla = Dla
+module Posix_path = Posix_path

lib_eio/utils/posix_path.ml

@@ -0,0 +1,49 @@
+(* Like [Filename.is_relative] but always using "/" as the separator. *)
+let is_relative = function
+  | "" -> true
+  | x -> x.[0] <> '/'
+
+(* Like [Filename.concat] but always using "/" as the separator. *)
+let concat a b =
+  let l = String.length a in
+  if l = 0 || a.[l - 1] = '/' then a ^ b
+  else a ^ "/" ^ b
+
+let join p1 p2 =
+  match p1, p2 with
+  | p1, "" -> concat p1 p2
+  | _, p2 when not (is_relative p2) -> p2
+  | ".", p2 -> p2
+  | p1, p2 -> concat p1 p2
+
+(* Drop the first [n] characters from [s]. *)
+let string_drop s n =
+  String.sub s n (String.length s - n)
+
+(* "/foo/bar//" -> "/foo/bar"
+   "///" -> "/"
+   "foo/bar" -> "foo/bar"
+ *)
+let remove_trailing_slashes s =
+  let rec aux i =
+    if i <= 1 || s.[i - 1] <> '/' then (
+      if i = String.length s then s
+      else String.sub s 0 i
+    ) else aux (i - 1)
+  in
+  aux (String.length s)
+
+let split p =
+  match remove_trailing_slashes p with
+  | "" -> None
+  | "/" -> None
+  | p ->
+    match String.rindex_opt p '/' with
+    | None -> Some ("", p)
+    | Some idx ->
+      let basename = string_drop p (idx + 1) in
+      let dirname =
+        if idx = 0 then "/"
+        else remove_trailing_slashes (String.sub p 0 idx)
+      in
+      Some (dirname, basename)

lib_eio/utils/posix_path.mli

@@ -0,0 +1,3 @@
+(** POSIX path syntax. *)
+
+include Eio.Fs.Pi.PATH

lib_eio_linux/fs.ml

@@ -169,6 +169,8 @@ end = struct
 
   let native t path =
     Some (native_internal t path)
+
+  include Eio_utils.Posix_path
 end
 and Dir_handler : sig
   val v : (Dir.t, [`Dir | `Close]) Eio.Resource.handler

lib_eio_posix/fs.ml

@@ -152,6 +152,8 @@ end = struct
 
   let native t path =
     Some (native_internal t path)
+
+  include Eio_utils.Posix_path
 end
 and Handler : sig
   val v : (Dir.t, [`Dir | `Close]) Eio.Resource.handler

lib_eio_windows/fs.ml

@@ -208,6 +208,8 @@ end = struct
 
   let native _t _path =
     failwith "TODO: Windows native"
+
+  include Eio_utils.Posix_path    (* todo: replace with Windows syntax *)
 end
 and Handler : sig
   val v : (Dir.t, [`Dir | `Close]) Eio.Resource.handler

tests/fs.md

@@ -273,8 +273,7 @@ Creating directories with nesting, symlinks, etc:
 # Split
 
 ```ocaml
-let fake_dir : Eio.Fs.dir_ty r = Eio.Resource.T ((), Eio.Resource.handler [])
-let split path = Eio.Path.split (fake_dir, path) |> Option.map (fun ((_, dirname), basename) -> dirname, basename)
+let split = Eio_utils.Posix_path.split
 ```
 
 ```ocaml