add optional JSON output of error messages for LSP integration

bin/raven.ml

@@ -283,32 +283,41 @@ let typecheck_only =
   let doc = "Only type-check input program but do not verify it." in
   Arg.(value & flag & info [ "typeonly" ] ~doc)
 
+let lsp_mode =
+  let doc = "Format error messages for LSP integration." in
+  Arg.(value & flag & info [ "lsp-mode" ] ~doc)
+
 let smt_timeout =
   let doc = "Timeout for SMT solver in ms." in 
   Arg.(value & opt int 10000 & info [ "smt-timeout" ] ~doc)
 
 let greeting = "Raven version " ^ Config.version
 
-let main () input_files no_greeting no_library typecheck_only prog_stats smt_timeout smt_diagnostics =
+let print_errors lsp_mode errs =
+  if lsp_mode then begin
+    Stdlib.print_endline (Error.errors_to_lsp_string errs);
+    Stdlib.exit 0
+  end
+  else begin
+    List.iter errs ~f:(fun e -> Logs.err (fun m -> m !"%{Error}" e));
+    Logs.debug (fun m ->
+        m "\n---------\n%s"
+        @@ Backtrace.to_string (Backtrace.Exn.most_recent ()));
+    Stdlib.exit 1 (* duplicates error output: `Error (false, "") *)
+  end
+
+let main () input_files no_greeting no_library typecheck_only lsp_mode prog_stats smt_timeout smt_diagnostics =
   if not no_greeting then Logs.app (fun m -> m "%s" greeting) else ();
   try `Ok (parse_and_check_all typecheck_only smt_timeout smt_diagnostics no_library prog_stats input_files) with
   | Sys_error s | Failure s | Invalid_argument s ->
-      Logs.err (fun m -> m "%s" s);
-      Logs.debug (fun m ->
-          m "\n---------\n%s"
-          @@ Backtrace.to_string (Backtrace.Exn.most_recent ()));
-      Stdlib.exit 1 (* `Error (false, s) <- duplicates error output *)
+    print_errors lsp_mode [Internal, Loc.dummy, s]
   | Error.Msg es ->
-      List.iter es ~f:(fun e -> Logs.err (fun m -> m !"%{Error}" e));
-      Logs.debug (fun m ->
-          m "\n---------\n%s"
-          @@ Backtrace.to_string (Backtrace.Exn.most_recent ()));
-      Stdlib.exit 1 (* duplicates error output: `Error (false, "") *)
-
+    print_errors lsp_mode es
+
 let main_cmd =
   let info = Cmd.info "raven" ~version:Config.version in
   Cmd.v info
     Term.(
-      ret (const main $ setup_config $ input_file $ no_greeting $ no_library $ typecheck_only $ prog_stats $ smt_timeout $ smt_diagnostics))
+      ret (const main $ setup_config $ input_file $ no_greeting $ no_library $ typecheck_only $ lsp_mode $ prog_stats $ smt_timeout $ smt_diagnostics))
 
 let () = Stdlib.exit (Cmd.eval main_cmd)

lib/util/error.ml

@@ -12,6 +12,17 @@ type error_kind =
   | Verification
   | RelatedLoc
 
+let error_kind_to_lsp_string = function
+  | Generic -> "Generic"
+  | Lexical -> "Lexical"
+  | Syntax -> "Syntax"
+  | Type -> "Type"
+  | Internal -> "Internal"
+  | Unsupported -> "Unsupported"
+  | Verification -> "Verification"
+  | RelatedLoc -> "RelatedLoc"
+
+
 let error_kind_to_string = function
   | Generic -> "Error"
   | Lexical -> "Lexical Error"
@@ -44,6 +55,14 @@ let to_string (kind, (loc : Loc.t), msg) =
           then Printf.sprintf "%s:%s" (flycheck_string_of_src_pos pos) msg*)
     Printf.sprintf !"%{Loc}%{String}%{String}." loc label msg
 
+let to_lsp_string ppf (kind, (loc : Loc.t), msg) =
+  Stdlib.Format.fprintf ppf !"@\n{ \"file\": \"%{String}\", \"start_line\": %d, \"start_col\": %d, \"end_line\": %d, \"end_col\": %d, \"kind\": \"%s\", \"message\": \"%s\" }"
+    (Loc.file_name loc) (Loc.start_line loc) (Loc.start_col loc) (Loc.end_line loc) (Loc.end_col loc) (error_kind_to_lsp_string kind) msg
+
+let errors_to_lsp_string errs =
+  let print_list ppf errs = Stdlib.Format.fprintf ppf "[@[<2>%a@]]" (Print.pr_list_comma to_lsp_string) errs in
+  Print.string_of_format print_list errs
+
 (** Predefined error messags *)
 
 let internal_error loc msg = fail loc ~lbl:Internal msg

lib/util/loc.ml

@@ -45,6 +45,10 @@ let file_name loc = loc.loc_start.pos_fname
 let to_end loc = { loc with loc_start = loc.loc_end }
 let to_start loc = { loc with loc_end = loc.loc_start }
 
+let start_index loc = loc.loc_start.pos_cnum
+let end_index loc = loc.loc_end.pos_cnum
+
+
 let merge l1 l2 =
   assert (String.equal (file_name l1) (file_name l2));
   let spos =