2.3.5: json_sax_dom_error_state base for the DOM SAX parsers (#5891)

Holds errored, allow_exceptions, parse_error() and is_errored(). The scalar
handlers stay in each class (parse hot path).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/input/json_sax.hpp

@@ -315,6 +315,52 @@ struct diagnostic_positions
 };
 #endif
 
+/*!
+@brief error state shared by the DOM-building SAX parsers
+
+Holds whether a parse error occurred and whether errors are thrown, and
+implements the parse_error() and is_errored() members of the SAX interface for
+json_sax_dom_parser and json_sax_dom_callback_parser.
+*/
+class json_sax_dom_error_state
+{
+  public:
+    explicit json_sax_dom_error_state(const bool allow_exceptions_) noexcept
+        : allow_exceptions(allow_exceptions_)
+    {}
+
+    // make class move-only
+    json_sax_dom_error_state(const json_sax_dom_error_state&) = delete;
+    json_sax_dom_error_state(json_sax_dom_error_state&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
+    json_sax_dom_error_state& operator=(const json_sax_dom_error_state&) = delete;
+    json_sax_dom_error_state& operator=(json_sax_dom_error_state&&) = delete; // the const member prevents assignment
+    ~json_sax_dom_error_state() = default;
+
+    template<class Exception>
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
+                     const Exception& ex)
+    {
+        errored = true;
+        static_cast<void>(ex);
+        if (allow_exceptions)
+        {
+            JSON_THROW(ex);
+        }
+        return false;
+    }
+
+    constexpr bool is_errored() const
+    {
+        return errored;
+    }
+
+  private:
+    /// whether a syntax error occurred
+    bool errored = false;
+    /// whether to throw exceptions in case of errors
+    const bool allow_exceptions = true;
+};
+
 /*!
 @brief SAX implementation to create a JSON value from SAX events
 
@@ -329,7 +375,7 @@ constructor contains the parsed value.
 @tparam BasicJsonType  the JSON type
 */
 template<typename BasicJsonType, typename InputAdapterType>
-class json_sax_dom_parser
+class json_sax_dom_parser : public json_sax_dom_error_state
 {
   public:
     using number_integer_t = typename BasicJsonType::number_integer_t;
@@ -345,7 +391,7 @@ class json_sax_dom_parser
     @param[in] allow_exceptions_  whether parse errors yield exceptions
     */
     explicit json_sax_dom_parser(BasicJsonType& r, const bool allow_exceptions_ = true, lexer_t* lexer_ = nullptr)
-        : root(r), allow_exceptions(allow_exceptions_), m_lexer_ref(lexer_)
+        : json_sax_dom_error_state(allow_exceptions_), root(r), m_lexer_ref(lexer_)
     {}
 
     // make class move-only
@@ -474,24 +520,6 @@ class json_sax_dom_parser
         return true;
     }
 
-    template<class Exception>
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
-                     const Exception& ex)
-    {
-        errored = true;
-        static_cast<void>(ex);
-        if (allow_exceptions)
-        {
-            JSON_THROW(ex);
-        }
-        return false;
-    }
-
-    constexpr bool is_errored() const
-    {
-        return errored;
-    }
-
   private:
 
     /*!
@@ -545,16 +573,12 @@ class json_sax_dom_parser
     std::vector<BasicJsonType*> ref_stack {};
     /// helper to hold the reference for the next object element
     BasicJsonType* object_element = nullptr;
-    /// whether a syntax error occurred
-    bool errored = false;
-    /// whether to throw exceptions in case of errors
-    const bool allow_exceptions = true;
     /// the lexer reference to obtain the current position
     lexer_t* m_lexer_ref = nullptr;
 };
 
 template<typename BasicJsonType, typename InputAdapterType>
-class json_sax_dom_callback_parser
+class json_sax_dom_callback_parser : public json_sax_dom_error_state
 {
   public:
     using number_integer_t = typename BasicJsonType::number_integer_t;
@@ -570,7 +594,7 @@ class json_sax_dom_callback_parser
                                  parser_callback_t cb,
                                  const bool allow_exceptions_ = true,
                                  lexer_t* lexer_ = nullptr)
-        : root(r), callback(std::move(cb)), allow_exceptions(allow_exceptions_), m_lexer_ref(lexer_)
+        : json_sax_dom_error_state(allow_exceptions_), root(r), callback(std::move(cb)), m_lexer_ref(lexer_)
     {
         keep_stack.push_back(true);
     }
@@ -837,24 +861,6 @@ class json_sax_dom_callback_parser
         return true;
     }
 
-    template<class Exception>
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
-                     const Exception& ex)
-    {
-        errored = true;
-        static_cast<void>(ex);
-        if (allow_exceptions)
-        {
-            JSON_THROW(ex);
-        }
-        return false;
-    }
-
-    constexpr bool is_errored() const
-    {
-        return errored;
-    }
-
   private:
 
     /// if there is a pending duplicate-key stash entry for this exact slot,
@@ -1096,12 +1102,8 @@ class json_sax_dom_callback_parser
     /// value is later rejected by the callback, instead of erasing the
     /// member entirely
     std::vector<std::pair<BasicJsonType*, BasicJsonType>> duplicate_key_stash {};
-    /// whether a syntax error occurred
-    bool errored = false;
     /// callback function
     const parser_callback_t callback = nullptr;
-    /// whether to throw exceptions in case of errors
-    const bool allow_exceptions = true;
     /// a discarded value for the callback
     BasicJsonType discarded = BasicJsonType::value_t::discarded;
     /// the lexer reference to obtain the current position