Fix C++11 ABI breakage when compiled with C++17 (#1668)

When JSONCPP_HAS_STRING_VIEW was defined, the library dropped the
`const char*` and `const String&` overloads for `operator[]`, `get`,
`removeMember`, and `isMember`, breaking ABI compatibility for projects
consuming the library with C++11.

This change unconditionally declares and defines the legacy overloads
so they are always exported, restoring compatibility.

Author: baylesj

include/json/value.h

@@ -501,7 +501,7 @@ class JSON_API Value {
   /// that name.
   /// \param key may contain embedded nulls.
   const Value& operator[](std::string_view key) const;
-#else
+#endif
   /// Access an object value by name, create a null member if it does not exist.
   /// \note Because of our implementation, keys are limited to 2^30 -1 chars.
   /// Exceeding that will cause an exception.
@@ -516,7 +516,6 @@ class JSON_API Value {
   /// that name.
   /// \param key may contain embedded nulls.
   const Value& operator[](const String& key) const;
-#endif
   /** \brief Access an object value by name, create a null member if it does not
    * exist.
    *
@@ -534,15 +533,14 @@ class JSON_API Value {
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   Value get(std::string_view key, const Value& defaultValue) const;
-#else
+#endif
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   Value get(const char* key, const Value& defaultValue) const;
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   /// \param key may contain embedded nulls.
   Value get(const String& key, const Value& defaultValue) const;
-#endif
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   /// \note key may contain embedded nulls.
@@ -589,12 +587,11 @@ class JSON_API Value {
   /// \post type() is unchanged
 #if JSONCPP_HAS_STRING_VIEW
   void removeMember(std::string_view key);
-#else
+#endif
   void removeMember(const char* key);
   /// Same as removeMember(const char*)
   /// \param key may contain embedded nulls.
   void removeMember(const String& key);
-#endif
   /** \brief Remove the named map member.
    *
    *  Update 'removed' iff removed.
@@ -603,12 +600,11 @@ class JSON_API Value {
    */
 #if JSONCPP_HAS_STRING_VIEW
   bool removeMember(std::string_view key, Value* removed);
-#else
+#endif
   bool removeMember(String const& key, Value* removed);
   /// Same as removeMember(const char* begin, const char* end, Value* removed),
   /// but 'key' is null-terminated.
   bool removeMember(const char* key, Value* removed);
-#endif
   /// Same as removeMember(String const& key, Value* removed)
   bool removeMember(const char* begin, const char* end, Value* removed);
   /** \brief Remove the indexed array element.
@@ -623,14 +619,13 @@ class JSON_API Value {
   /// Return true if the object has a member named key.
   /// \param key may contain embedded nulls.
   bool isMember(std::string_view key) const;
-#else
+#endif
   /// Return true if the object has a member named key.
   /// \note 'key' must be null-terminated.
   bool isMember(const char* key) const;
   /// Return true if the object has a member named key.
   /// \param key may contain embedded nulls.
   bool isMember(const String& key) const;
-#endif
   /// Same as isMember(String const& key)const
   bool isMember(const char* begin, const char* end) const;
 

src/lib_json/json_value.cpp

@@ -1200,7 +1200,7 @@ const Value& Value::operator[](std::string_view key) const {
 Value& Value::operator[](std::string_view key) {
   return resolveReference(key.data(), key.data() + key.length());
 }
-#else
+#endif
 const Value& Value::operator[](const char* key) const {
   Value const* found = find(key, key + strlen(key));
   if (!found)
@@ -1221,7 +1221,6 @@ Value& Value::operator[](const char* key) {
 Value& Value::operator[](const String& key) {
   return resolveReference(key.data(), key.data() + key.length());
 }
-#endif
 
 Value& Value::operator[](const StaticString& key) {
   return resolveReference(key.c_str());
@@ -1265,14 +1264,13 @@ Value Value::get(char const* begin, char const* end,
 Value Value::get(std::string_view key, const Value& defaultValue) const {
   return get(key.data(), key.data() + key.length(), defaultValue);
 }
-#else
+#endif
 Value Value::get(char const* key, Value const& defaultValue) const {
   return get(key, key + strlen(key), defaultValue);
 }
 Value Value::get(String const& key, Value const& defaultValue) const {
   return get(key.data(), key.data() + key.length(), defaultValue);
 }
-#endif
 
 bool Value::removeMember(const char* begin, const char* end, Value* removed) {
   if (type() != objectValue) {
@@ -1292,14 +1290,13 @@ bool Value::removeMember(const char* begin, const char* end, Value* removed) {
 bool Value::removeMember(std::string_view key, Value* removed) {
   return removeMember(key.data(), key.data() + key.length(), removed);
 }
-#else
+#endif
 bool Value::removeMember(const char* key, Value* removed) {
   return removeMember(key, key + strlen(key), removed);
 }
 bool Value::removeMember(String const& key, Value* removed) {
   return removeMember(key.data(), key.data() + key.length(), removed);
 }
-#endif
 
 #ifdef JSONCPP_HAS_STRING_VIEW
 void Value::removeMember(std::string_view key) {
@@ -1312,7 +1309,7 @@ void Value::removeMember(std::string_view key) {
                      CZString::noDuplication);
   value_.map_->erase(actualKey);
 }
-#else
+#endif
 void Value::removeMember(const char* key) {
   JSON_ASSERT_MESSAGE(type() == nullValue || type() == objectValue,
                       "in Json::Value::removeMember(): requires objectValue");
@@ -1323,7 +1320,6 @@ void Value::removeMember(const char* key) {
   value_.map_->erase(actualKey);
 }
 void Value::removeMember(const String& key) { removeMember(key.c_str()); }
-#endif
 
 bool Value::removeIndex(ArrayIndex index, Value* removed) {
   if (type() != arrayValue) {
@@ -1357,14 +1353,13 @@ bool Value::isMember(char const* begin, char const* end) const {
 bool Value::isMember(std::string_view key) const {
   return isMember(key.data(), key.data() + key.length());
 }
-#else
+#endif
 bool Value::isMember(char const* key) const {
   return isMember(key, key + strlen(key));
 }
 bool Value::isMember(String const& key) const {
   return isMember(key.data(), key.data() + key.length());
 }
-#endif
 
 Value::Members Value::getMemberNames() const {
   JSON_ASSERT_MESSAGE(