repo: fixed incorrect relative link computation

when detecting redundancies in repo I needed to test if a path was a
prefix of another, with *directory* granularity. Problem was I tested
that at *character* granularity, causing foo/bar.fa and foo/bar.fa.gz
to be detected as redundant. However for the relevant meaning when
generating repo, only foo is considered redundant.

lib/bistro.ml

@@ -48,6 +48,15 @@ module Path = struct
     | "/" :: t -> "/" ^ (to_string t)
     | p -> List.reduce_exn p ~f:Filename.concat
 
+  let rec is_prefix ~prefix u =
+    match prefix, u with
+    | [], _ -> true
+    | _, [] -> false
+    | h_p :: t_p, h_u :: t_u ->
+      h_p = h_u && is_prefix ~prefix:t_p t_u
+
+  let is_strict_prefix ~prefix u =
+    prefix <> u && is_prefix ~prefix u
 end
 
 

lib/bistro.mli

@@ -39,6 +39,9 @@ module Path : sig
       can be used to go from [dirA] to [dirB]. @raise
       [Invalid_argument] if [dirA] is relative. *)
   val make_relative : ?from:string -> string -> t
+
+  val is_prefix : prefix:t -> t -> bool
+  val is_strict_prefix : prefix:t -> t -> bool
 end
 
 type id = string

lib/utils/repo.ml

@@ -25,13 +25,13 @@ let item path w = Repo_item (path, w)
 
 let ( %> ) path w = item path w
 
-let is_strict_prefix ~prefix u =
-  String.length prefix < String.length u
-  && String.is_prefix ~prefix u
-
 let find_bottom items item =
+  let module P = Bistro.Path in
   let f min_item candidate =
-    if is_strict_prefix ~prefix:candidate.target_path min_item.target_path
+    if
+      P.is_strict_prefix
+        ~prefix:(P.of_string candidate.target_path)
+        (P.of_string min_item.target_path)
     then candidate
     else min_item
   in