Create a diff implementation

dune-project

@@ -1,2 +1,4 @@
-(lang dune 1.0)
+(lang dune 3.0)
 (name patch)
+(executables_implicit_empty_intf true)
+(formatting disabled)

patch.opam

@@ -9,7 +9,7 @@ license: "ISC"
 
 depends: [
   "ocaml" {>= "4.04.2"}
-  "dune"
+  "dune" {>= "3.0"}
   "alcotest" {with-test & >= "0.7.0"}
   "crowbar" {with-test}
 ]

src/patch.ml

@@ -323,3 +323,65 @@ let patch filedata diff =
       | true, true -> lines
     in
     Some (String.concat "\n" lines)
+
+let diff_op operation a b =
+  let rec aux ~mine_start ~mine_len ~mine ~their_start ~their_len ~their l1 l2 =
+    let create_diff ~mine_no_nl ~their_no_nl =
+      let hunks =
+        if mine = [] && their = [] then
+          assert false
+        else
+          let mine = List.rev mine in
+          let their = List.rev their in
+          [{mine_start; mine_len; mine; their_start; their_len; their}]
+      in
+      {operation; hunks; mine_no_nl; their_no_nl}
+    in
+    match l1, l2 with
+    | [], [] | [""], [""] when mine = [] && their = [] -> assert false
+    | [], [] -> Some (create_diff ~mine_no_nl:true ~their_no_nl:true)
+    | [""], [] -> Some (create_diff ~mine_no_nl:false ~their_no_nl:true)
+    | [], [""] -> Some (create_diff ~mine_no_nl:true ~their_no_nl:false)
+    | [""], [""] -> Some (create_diff ~mine_no_nl:false ~their_no_nl:false)
+    | [a; ""], [b] when b <> "" ->
+        aux
+          ~mine_start ~mine_len:(mine_len + 1) ~mine:(a :: mine)
+          ~their_start ~their_len:(their_len + 1) ~their:(b :: their)
+          [""] []
+    | [a], [b; ""] when a <> "" ->
+        aux
+          ~mine_start ~mine_len:(mine_len + 1) ~mine:(a :: mine)
+          ~their_start ~their_len:(their_len + 1) ~their:(b :: their)
+          [] [""]
+    | a::l1, ([] | [""]) ->
+        aux
+          ~mine_start ~mine_len:(mine_len + 1) ~mine:(a :: mine)
+          ~their_start ~their_len ~their
+          l1 l2
+    | ([] | [""]), b::l2 ->
+        aux
+          ~mine_start ~mine_len ~mine
+          ~their_start ~their_len:(their_len + 1) ~their:(b :: their)
+          l1 l2
+    | a::l1, b::l2 when mine = [] && their = [] && String.equal a b ->
+        aux
+          ~mine_start:(mine_start + 1) ~mine_len ~mine
+          ~their_start:(their_start + 1) ~their_len ~their
+          l1 l2
+    | a::l1, b::l2 ->
+        aux
+          ~mine_start ~mine_len:(mine_len + 1) ~mine:(a :: mine)
+          ~their_start ~their_len:(their_len + 1) ~their:(b :: their)
+          l1 l2
+  in
+  aux
+    ~mine_start:0 ~mine_len:0 ~mine:[]
+    ~their_start:0 ~their_len:0 ~their:[]
+    (to_lines a) (to_lines b)
+
+let diff operation a b = match a, b with
+  | None, None -> invalid_arg "no input given"
+  | None, Some b -> diff_op operation "" b
+  | Some a, None -> diff_op operation a ""
+  | Some a, Some b when String.equal a b -> None (* NOTE: Optimization *)
+  | Some a, Some b -> diff_op operation a b

src/patch.mli

@@ -54,3 +54,9 @@ val to_diffs : string -> t list
 val patch : string option -> t -> string option
 (** [patch file_contents diff] applies [diff] on [file_contents], resulting in
     the new file contents (or None if deleted). *)
+
+val diff : operation -> string option -> string option -> t option
+(** [diff operation content_a content_b] creates a diff between
+    [content_a] and [content_b]. Returns [None] if no changes could be detected.
+
+    @raise Invalid_argument if both [content_a] and [content_b] are [None]. *)

test/dune

@@ -3,8 +3,8 @@
  (modules test)
  (libraries patch alcotest))
 
-(alias
- (name runtest)
+(rule
+ (alias runtest)
  (deps (source_tree data) (:< test.exe))
  (action (run %{<})))