Speed up Store.last-modified by comparing hashes instead of file co…

…ntents

src/irmin/store.ml

@@ -1153,9 +1153,9 @@ module Make (B : Backend.S) = struct
         let current, current_depth = Heap.pop_minimum heap in
         let parents = Commit.parents current in
         let tree = Commit.tree current in
-        let* current_value = Tree.find tree key in
+        let* current_tree = Tree.find_tree tree key in
         if List.length parents = 0 then
-          if current_value <> None then Lwt.return (current :: acc)
+          if current_tree <> None then Lwt.return (current :: acc)
           else Lwt.return acc
         else
           let max_depth =
@@ -1173,9 +1173,9 @@ module Make (B : Backend.S) = struct
                         Heap.add heap (commit, current_depth + 1)
                     in
                     let tree = Commit.tree commit in
-                    let+ e = Tree.find tree key in
-                    match (e, current_value) with
-                    | Some x, Some y -> not (equal_contents x y)
+                    let+ e = Tree.find_tree tree key in
+                    match (e, current_tree) with
+                    | Some x, Some y -> Tree.hash x <> Tree.hash y
                     | Some _, None -> true
                     | None, Some _ -> true
                     | _, _ -> false)

src/irmin/store_intf.ml

@@ -1006,10 +1006,9 @@ module type S_generic_key = sig
       head is not set) and stopping at [min] if specified. *)
 
   val last_modified : ?depth:int -> ?n:int -> t -> path -> commit list Lwt.t
-  (** [last_modified ?number c k] is the list of the last [number] commits that
-      modified [path], in ascending order of date. [depth] is the maximum depth
-      to be explored in the commit graph, if any. Default value for [number] is
-      1. *)
+  (** [last_modified ?n c k] is the list of the last [n] commits that modified
+      [path], in ascending order of date. [depth] is the maximum depth to be
+      explored in the commit graph, if any. Default value for [n] is 1. *)
 
   (** Manipulate branches. *)
   module Branch : sig