make dotty field optional in json

Summary:
public
The "dotty" field in json reports is only used when reporting retain cycles. It
makes sense not to emit it by default (when it's `None`).

Reviewed By: akotulski

Differential Revision: D2891320

fb-gh-sync-id: 54292a9

infer/src/backend/inferprint.ml

@@ -188,8 +188,7 @@ let error_desc_to_plain_string error_desc =
   pp_to_string pp ()
 
 let error_desc_to_dotty_string error_desc =
-  let dotty_opt = Localise.error_desc_get_dotty error_desc in
-  match dotty_opt with Some s -> s | None -> ""
+  Localise.error_desc_get_dotty error_desc
 
 let error_desc_to_xml_string error_desc =
   let pp fmt () = F.fprintf fmt "%a" Localise.pp_error_desc error_desc in

infer/src/backend/jsonbug.atd

@@ -31,7 +31,7 @@ type jsonbug = {
   key : int;
   qualifier_tags : tag_value_record list;
   hash : int;
-  dotty : string;
+  ?dotty : string option;
   ?infer_source_loc: loc option;
 }