Improved throw error message in json_serializer

The throw error message now shows the type
that it was expecting and the actual type that
is having.

Added another constructor in json_exceptiont that
uses the json field type.

Added enum_out_of_ranget exception class that
inherits from std::out_of_range in enum_out_of_range.h.

Added json_kind_out_of_ranget exception class
in json_kind_out_of_range.h that
extends enum_out_of_ranget, used for a better way
of describing exceptions when a JSON kind field
is not in the enum's possible values.

Used json_kind_out_of_ranget exception class
in json_exceptiont class.

Author: mariusmc92

src/util/enum_out_of_range.h

@@ -0,0 +1,36 @@
+/*******************************************************************\
+
+Module: enum_out_of_range
+
+Author: Marius-Constantin Melemciuc
+
+Purpose: Exception to report enums that are out of their
+         expected range.
+
+Date: April 2017
+
+@ Copyright Diffblue, Ltd.
+
+\*******************************************************************/
+
+#ifndef CPROVER_UTIL_ENUM_OUT_OF_RANGE_H
+#define CPROVER_UTIL_ENUM_OUT_OF_RANGE_H
+
+#include <stdexcept>
+
+
+/*******************************************************************\
+
+ Class: enum_out_of_ranget
+
+ Purpose: The type of exception thrown when an enum instance
+          is out of the enum's range.
+
+\*******************************************************************/
+class enum_out_of_ranget:public std::out_of_range
+{
+public:
+  using std::out_of_range::out_of_range;
+};
+
+#endif // CPROVER_UTIL_ENUM_OUT_OF_RANGE_H

src/util/json_kind_out_of_range.h

@@ -0,0 +1,41 @@
+/*******************************************************************\
+
+Module: json_kind_out_of_range
+
+Author: Marius-Constantin Melemciuc
+
+Purpose: Exception to report JSON kind that is out of the
+         expected range.
+
+Date: April 2017
+
+@ Copyright Diffblue, Ltd.
+
+\*******************************************************************/
+
+#ifndef CPROVER_UTIL_JSON_KIND_OUT_OF_RANGE_H
+#define CPROVER_UTIL_JSON_KIND_OUT_OF_RANGE_H
+
+#include "enum_out_of_range.h"
+
+
+/*******************************************************************\
+
+ Class: json_kind_out_of_ranget
+
+ Purpose: The type of exception thrown when the kind field of a JSON
+          is not of a defined enum type.
+
+\*******************************************************************/
+class json_kind_out_of_ranget:public enum_out_of_ranget
+{
+public:
+  using enum_out_of_ranget::enum_out_of_ranget;
+
+  json_kind_out_of_ranget()
+    : enum_out_of_ranget("Invalid jsont kind")
+  {
+  }
+};
+
+#endif // CPROVER_UTIL_JSON_KIND_OUT_OF_RANGE_H

src/util/json_serializer.cpp

@@ -22,7 +22,9 @@ json_objectt json_serializert::load_json(
   if(parse_json(file_path, message_handler, json))
     throw json_exceptiont("Couldn't parse JSON");
   if(!json.is_object())
-    throw json_exceptiont("JSON for serializaton wasn't an object");
+    throw json_exceptiont(
+      "Tried to read an object but JSON contained a {0}.",
+      json);
   return static_cast<json_objectt &>(json);
 }
 
@@ -141,7 +143,9 @@ void json_serializert::serialize_object(
   std::function<void(serializert &serializer)> serialize)
 {
   if(is_for_reading() && !json[name].is_object())
-    throw json_exceptiont("JSON object was not an object");
+    throw json_exceptiont(
+      "Tried to read an object but JSON contained a {0}.",
+      json[name]);
   json_serializert serializer(this, json[name].make_object(), is_for_reading());
   serialize(serializer);
 }
@@ -151,11 +155,15 @@ void json_serializert::read_array(
   std::function<void(serializert &serializer)> read_elt)
 {
   if(!json[name].is_array())
-    throw json_exceptiont("JSON array was not an array");
+    throw json_exceptiont(
+      "Tried to read an array but JSON contained a {0}.",
+      json[name]);
   for(jsont json_elt : json[name].array)
   {
     if(!json_elt.is_object())
-      throw json_exceptiont("JSON object was not an object");
+      throw json_exceptiont(
+        "Tried to read an object but JSON contained a {0}.",
+        json[name]);
     json_serializert serializer(this, json_elt.make_object(), is_for_reading());
     read_elt(serializer);
   }

src/util/json_serializer.h

@@ -11,10 +11,15 @@ Purpose: Generic serialization of object hierarchies to JSON.
 #ifndef CPROVER_UTIL_JSON_SERIALIZER_H
 #define CPROVER_UTIL_JSON_SERIALIZER_H
 
+#include "json_kind_out_of_range.h"
+
 #include <util/serializer.h>
 #include <util/json.h>
 #include <util/message.h>
 #include <json/json_parser.h>
+
+#include <boost/algorithm/string/replace.hpp>
+
 #include <fstream>
 #include <algorithm>
 
@@ -40,6 +45,35 @@ class json_exceptiont:public std::runtime_error
     : std::runtime_error(what_arg)
   {
   }
+
+  json_exceptiont(std::string what_arg, const jsont &json)
+    : std::runtime_error(construct_error_message(std::move(what_arg), json))
+  {
+  }
+
+private:
+  static std::string format_jsont(const jsont &json)
+  {
+    switch(json.kind)
+    {
+      case jsont::J_STRING: return "string (" + json.value + ")";
+      case jsont::J_NUMBER: return "number (" + json.value + ")";
+      case jsont::J_OBJECT: return "object";
+      case jsont::J_ARRAY: return "array";
+      case jsont::J_TRUE: return "bool (true)";
+      case jsont::J_FALSE: return "bool (false)";
+      case jsont::J_NULL: return "null";
+      default: throw json_kind_out_of_ranget();
+    }
+  }
+
+  std::string construct_error_message(
+    std::string error_message,
+    const jsont &json)
+  {
+    boost::replace_all(error_message, "{0}", format_jsont(json));
+    return error_message;
+  }
 };
 
 /*******************************************************************\