Split definition into a dedicated api

Just like we did for hover

src/EditorSupportCommands.ml

@@ -192,3 +192,65 @@ let hover ~path ~line ~char =
       hover state ~file ~line ~char ~extra ~package
   in
   print_endline result
+
+let definition state ~file ~line ~char ~extra ~package =
+  let open TopTypes in
+  let locations =
+    extra.SharedTypes.locations
+    |> List.filter (fun (l, _) -> not l.Location.loc_ghost)
+  in
+  let locations =
+    let pos = (line, char) in
+    let pos = Utils.cmtLocFromVscode pos in
+    match References.locForPos ~extra:{extra with locations} pos with
+    | None -> []
+    | Some l -> [l]
+  in
+  let locationsInfo =
+    locations
+    |> Utils.filterMap (fun (_, loc) ->
+           let locIsModule =
+             match loc with
+             | SharedTypes.LModule _ | TopLevelModule _ -> true
+             | TypeDefinition _ | Typed _ | Constant _ | Explanation _ -> false
+           in
+           let uriLocOpt =
+             References.definitionForLoc ~pathsForModule:package.pathsForModule
+               ~file ~getUri:(State.fileForUri state)
+               ~getModule:(State.fileForModule state ~package)
+               loc
+           in
+           let def, skipZero =
+             match uriLocOpt with
+             | None -> (None, false)
+             | Some (uri2, loc) ->
+               let posIsZero {Lexing.pos_lnum; pos_bol; pos_cnum} =
+                 pos_lnum = 1 && pos_cnum - pos_bol = 0
+               in
+               (* Skip if range is all zero, unless it's a module *)
+               let skipZero =
+                 (not locIsModule) && loc.loc_start |> posIsZero
+                 && loc.loc_end |> posIsZero
+               in
+               let open Protocol in
+               ( Some {uri = Uri2.toString uri2; range = Utils.cmtLocToRange loc},
+                 skipZero )
+           in
+           let skip = skipZero || def = None in
+           match skip with true -> None | false -> def)
+  in
+  match locationsInfo with
+  | [] -> Protocol.null
+  | head :: _ -> Protocol.stringifyLocation head
+
+let definition ~path ~line ~char =
+  let state = TopTypes.empty () in
+  let filePath = Files.maybeConcat (Unix.getcwd ()) path in
+  let uri = Uri2.fromPath filePath in
+  let result =
+    match State.getFullFromCmt ~state ~uri with
+    | Error _message -> Protocol.null
+    | Ok (package, {file; extra}) ->
+      definition state ~file ~line ~char ~extra ~package
+  in
+  print_endline result

src/Protocol.ml

@@ -1,5 +1,15 @@
 let array l = "[" ^ (String.concat ", " l) ^ "]"
 
+type position = {
+  line: int;
+  character: int;
+}
+
+type range = {
+  start: position;
+  end_: position;
+}
+
 type markupContent = {
   kind: string;
   value: string;
@@ -17,6 +27,19 @@ type hover = {
   contents: string;
 }
 
+type location = {
+  uri: string;
+  range: range;
+}
+
+let stringifyPosition p =
+   Printf.sprintf {|{"line": "%i", "character": "%i"}|} p.line p.character
+
+let stringifyRange r =
+   Printf.sprintf {|{"start": "%s", "end": "%s"}|}
+    (stringifyPosition r.start)
+    (stringifyPosition r.end_)
+
 let stringifyMarkupContent (m: markupContent) =
   Printf.sprintf {|{"kind": "%s", "value": "%s"}|}
   m.kind (String.escaped m.value)
@@ -39,4 +62,9 @@ let stringifyHover h =
   Printf.sprintf {|{"contents": "%s"}|}
   (String.escaped h.contents)
 
+let stringifyLocation h =
+  Printf.sprintf {|{"uri": "%s", "range": "%s"}|}
+  (String.escaped h.uri)
+  (stringifyRange h.range)
+
 let null = "null"

src/RescriptEditorSupport.ml

@@ -40,6 +40,10 @@ Options:
   hover: get inferred type for Foo.res at line 10 column 2:
 
     rescript-editor-support.exe hover src/Foo.res 10 2
+
+  definition: get inferred type for Foo.res at line 10 column 2:
+
+    rescript-editor-support.exe definition src/Foo.res 10 2
 |}
 
 let showHelp () = prerr_endline help
@@ -53,6 +57,8 @@ let main () =
       ~char:(int_of_string char) ~currentFile
   | _opts, ["hover"; path; line; char] ->
     EditorSupportCommands.hover ~path ~line:(int_of_string line) ~char:(int_of_string char)
+  | _opts, ["definition"; path; line; char] ->
+    EditorSupportCommands.definition ~path ~line:(int_of_string line) ~char:(int_of_string char)
   | _ ->
     showHelp ();
     exit 1

src/Utils.ml

@@ -41,6 +41,16 @@ let endsWith s suffix =
 
 let cmtLocFromVscode (line, col) = (line + 1, col)
 
+let cmtLocToPosition {Lexing.pos_lnum; pos_cnum; pos_bol} = Protocol.{
+  line = pos_lnum - 1;
+  character = pos_cnum - pos_bol;
+}
+
+let cmtLocToRange {Location.loc_start; loc_end} = Protocol.{
+  start = cmtLocToPosition loc_start;
+  end_ = cmtLocToPosition loc_end;
+}
+
 let locWithinLoc inner outer =
   let open Location in
   inner.loc_start.pos_cnum >= outer.loc_start.pos_cnum