feature(lsp): low level zipper api (#1078)

Signed-off-by: Rudi Grinberg <[email protected]>

Author: rgrinberg

lsp/src/string_zipper.ml

@@ -39,6 +39,8 @@ let of_string s =
   ; line = 0
   }
 
+let offset t = t.abs_pos + t.rel_pos
+
 let length =
   let f acc sub = acc + Substring.length sub in
   fun { abs_pos = _; current; left; right; rel_pos = _; line = _ } ->

lsp/src/string_zipper.mli

@@ -30,6 +30,8 @@ val drop_until : t -> t -> t
 val apply_change :
   t -> Types.Range.t -> [ `UTF16 | `UTF8 ] -> replacement:string -> t
 
+val offset : t -> int
+
 module Private : sig
   type zipper := t
 

lsp/src/text_document.ml

@@ -104,3 +104,11 @@ let apply_text_document_edits t (edits : TextEdit.t list) =
   let text = apply_changes t.zipper t.position_encoding edits in
   let zipper = String_zipper.of_string text in
   { t with text = Some text; zipper }
+
+module Expert = struct
+  let goto t pos =
+    let zipper = String_zipper.goto_position t.zipper pos `UTF8 in
+    { t with zipper }
+
+  let offset t = String_zipper.offset t.zipper
+end

lsp/src/text_document.mli

@@ -30,3 +30,15 @@ val set_version : t -> version:int -> t
     when multiple inserts are done in the same position. All the offsets are
     interpreted relative to the original document. *)
 val apply_text_document_edits : t -> TextEdit.t list -> t
+
+module Expert : sig
+  (** These functions allow one to work with the underlying zipper. This gives
+      the opportunity for better performance on chained edits. *)
+
+  (** [goto t pos] move the zipper of [t] to [pos]. [pos] must be in utf8 *)
+  val goto : t -> Position.t -> t
+
+  (** [offset t] return the global offset in the string where the zipper is
+      currently focused *)
+  val offset : t -> int
+end