Add RAPIDJSON_NOEXCEPT_ASSERT

This is an alternative implementation to Tencent#1284 to handle
asserts in noexcept contexts.

Closes Tencent#1280.

Author: pah

include/rapidjson/document.h

@@ -37,9 +37,6 @@ RAPIDJSON_DIAG_OFF(4244) // conversion from kXxxFlags to 'uint16_t', possible lo
 
 #ifdef __GNUC__
 RAPIDJSON_DIAG_OFF(effc++)
-#if __GNUC__ >= 6
-RAPIDJSON_DIAG_OFF(terminate) // ignore throwing RAPIDJSON_ASSERT in RAPIDJSON_NOEXCEPT functions
-#endif
 #endif // __GNUC__
 
 #ifndef RAPIDJSON_NOMEMBERITERATORCLASS
@@ -625,11 +622,11 @@ class GenericValue {
         \note Default content for number is zero.
     */
     explicit GenericValue(Type type) RAPIDJSON_NOEXCEPT : data_() {
-        static const uint16_t defaultFlags[7] = {
+        static const uint16_t defaultFlags[] = {
             kNullFlag, kFalseFlag, kTrueFlag, kObjectFlag, kArrayFlag, kShortStringFlag,
             kNumberAnyFlag
         };
-        RAPIDJSON_ASSERT(type >= kNullType && type <= kNumberType);
+        RAPIDJSON_NOEXCEPT_ASSERT(type >= kNullType && type <= kNumberType);
         data_.f.flags = defaultFlags[type];
 
         // Use ShortString to store empty string.
@@ -831,9 +828,10 @@ class GenericValue {
     /*! \param rhs Source of the assignment. It will become a null value after assignment.
     */
     GenericValue& operator=(GenericValue& rhs) RAPIDJSON_NOEXCEPT {
-        RAPIDJSON_ASSERT(this != &rhs);
-        this->~GenericValue();
-        RawAssign(rhs);
+        if (RAPIDJSON_LIKELY(this != &rhs)) {
+            this->~GenericValue();
+            RawAssign(rhs);
+        }
         return *this;
     }
 

include/rapidjson/rapidjson.h

@@ -598,6 +598,25 @@ RAPIDJSON_NAMESPACE_END
 
 //!@endcond
 
+//! Assertion (in non-throwing contexts).
+ /*! \ingroup RAPIDJSON_CONFIG
+    Some functions provide a \c noexcept guarantee, if the compiler supports it.
+    In these cases, the \ref RAPIDJSON_ASSERT macro cannot be overridden to
+    throw an exception.  This macro adds a separate customization point for
+    such cases.
+
+    Defaults to C \c assert() (as \ref RAPIDJSON_ASSERT), if \c noexcept is
+    supported, and to \ref RAPIDJSON_ASSERT otherwise.
+ */
+#ifndef RAPIDJSON_NOEXCEPT_ASSERT
+#if RAPIDJSON_HAS_CXX11_NOEXCEPT
+#include <cassert>
+#define RAPIDJSON_NOEXCEPT_ASSERT(x) assert(x)
+#else
+#define RAPIDJSON_NOEXCEPT_ASSERT(x) RAPIDJSON_ASSERT(x)
+#endif // RAPIDJSON_HAS_CXX11_NOEXCEPT
+#endif // RAPIDJSON_NOEXCEPT_ASSERT
+
 ///////////////////////////////////////////////////////////////////////////////
 // new/delete