Rework some user error messages.

src/main.ml

@@ -150,7 +150,7 @@ let verify_json ?memlimit ?timelimit ?outfile json =
     match query.output_file with
     | None ->
       Logging.code_error ~src:Logs.default (fun m ->
-        m "No output file found to record verification results")
+        m "No output file specified to record verification results")
     | Some outfile -> outfile
   in
   record_verification_result verification_results outfile

src/verification_types.ml

@@ -133,11 +133,11 @@ module Query = struct
       match of_yojson (Yojson.Safe.from_file s) with
       | Ok t -> t
       | Error msg ->
-        invalid_arg
-          (Fmt.str "Unrecognized JSON configuration in file '%s' (%s)" s msg)
+        Logging.user_error (fun m ->
+          m "Unrecognized JSON configuration in file '%s' (%s)" s msg)
       | exception Yojson.Json_error msg ->
-        failwith
-          (Fmt.str "Unexpected error while parsing JSON file '%s' (%s)" s msg)
+        Logging.user_error (fun m ->
+          m "Unexpected error while parsing JSON file '%s' (%s)" s msg)
     in
     let query =
       (* Precedence to the command line option, if any. *)
@@ -160,8 +160,8 @@ module Query = struct
       | None ->
         Logging.user_error (fun m ->
           m
-            "@[No output file while creating verification query from JSON \
-             file@]"))
+            "@[No output file specified while creating verification query from \
+             JSON file@]"))
     | Some _ as output_file -> { query with output_file }
 
   let pretty fmt = Fmt.fmt "%a" fmt pp