fix exception handling in find-refs command

Summary:
if i'm reading it correctly, if the server raises an exception during
`find-refs`, it writes to the server log and returns `None` which is not
marshaled over the channel so the client blocks until it times out.

instead, it should return an error to the user.

Reviewed By: avikchaudhuri

Differential Revision: D5088871

fbshipit-source-id: 35c4c629d1784b4b1f3a6890ddd6e77428b0aea3

src/commands/findRefsCommand.ml

@@ -74,16 +74,23 @@ let main option_values root json pretty strip_root path args () =
   ServerProt.cmd_to_channel oc
     (ServerProt.FIND_REFS (file, line, column));
   (* command result will be a position structure with full file path *)
-  let locs: Loc.t list = Timeout.input_value ic in
-  (* format output *)
-  print_endline @@
-    if json || pretty
-    then Hh_json.(json_to_string ~pretty @@
-      JSON_Array (List.map (Reason.json_of_loc ~strip_root) locs)
-    )
-    else String.concat "\n" @@
-      if option_values.from = "vim" || option_values.from = "emacs"
-      then List.map (Errors.Vim_emacs_output.string_of_loc ~strip_root) locs
-      else List.map (range_string_of_loc ~strip_root) locs
+  let response: ServerProt.find_refs_response = Timeout.input_value ic in
+  match response with
+  | Ok locs ->
+    (* format output *)
+    print_endline @@
+      if json || pretty
+      then Hh_json.(json_to_string ~pretty @@
+        JSON_Array (List.map (Reason.json_of_loc ~strip_root) locs)
+      )
+      else String.concat "\n" @@
+        if option_values.from = "vim" || option_values.from = "emacs"
+        then List.map (Errors.Vim_emacs_output.string_of_loc ~strip_root) locs
+        else List.map (range_string_of_loc ~strip_root) locs
+  | Error exn_msg ->
+    Utils_js.prerr_endlinef
+      "Could not find refs for %s:%d:%d\n%s"
+      (ServerProt.file_input_get_filename file) line column exn_msg
+
 
 let command = CommandSpec.command spec main

src/server/server.ml

@@ -382,13 +382,9 @@ let collate_errors =
           | _, Some cx, _, _ -> cx
           | _  -> failwith "Couldn't parse file"
         in
-        Some (FindRefs_js.result cx state)
+        Ok (FindRefs_js.result cx state)
       with exn ->
-        Hh_logger.warn
-          "Could not find refs for %s:%d:%d\n%s"
-          filename line col
-          (Printexc.to_string exn);
-        None
+        Error (Printexc.to_string exn)
     in
     FindRefs_js.unset_hooks ();
     result
@@ -591,10 +587,6 @@ let collate_errors =
       Marshal.to_channel oc msg [];
       flush oc
     in
-    let marshal_option = function
-      | Some msg -> marshal msg
-      | None -> ()
-    in
     let options = genv.ServerEnv.options in
     let { ServerProt.client_logging_context; command; } = msg in
     begin match command with
@@ -619,8 +611,8 @@ let collate_errors =
         (find_module ~options (moduleref, filename): filename option)
           |> marshal
     | ServerProt.FIND_REFS (fn, line, char) ->
-        (find_refs ~options (fn, line, char): Loc.t list option)
-          |> marshal_option
+        (find_refs ~options (fn, line, char): ServerProt.find_refs_response)
+          |> marshal
     | ServerProt.FORCE_RECHECK (files) ->
         Marshal.to_channel oc () [];
         flush oc;

src/server/serverProt.ml

@@ -75,6 +75,7 @@ type dump_types_response = (
   (Loc.t * string * string * string option * Reason.t list) list,
   Loc.t * string
 ) result
+type find_refs_response = (Loc.t list, string) result
 type get_def_response = (Loc.t, string) result
 type infer_type_response = (
   Loc.t * string option * string option * Reason.t list,