Show warning when reading/writing ID3v2 frames not matching the tag version

id3/id3v2frame.cpp

@@ -195,6 +195,15 @@ void Id3v2Frame::parse(BinaryReader &reader, std::uint32_t version, std::uint32_
         }
     }
 
+    // add a warning if a frame appears in an ID3v2 tag known not to support it
+    if (version <= 3 && Id3v2FrameIds::isOnlyId3v24Id(version < 3 ? Id3v2FrameIds::convertToLongId(id()) : id())) {
+        diag.emplace_back(DiagLevel::Warning,
+            argsToString("The frame is only supported in ID3v2.4 and newer but the tag's version is ID3v2.", version, '.'), context);
+    } else if (version > 3 && Id3v2FrameIds::isPreId3v24Id(id())) {
+        diag.emplace_back(DiagLevel::Warning,
+            argsToString("The frame is only supported in ID3v2.3 and older but the tag's version is ID3v2.", version, '.'), context);
+    }
+
     // frame size mustn't be 0
     if (m_dataSize <= 0) {
         diag.emplace_back(DiagLevel::Warning, "The frame size is 0.", context);
@@ -498,6 +507,19 @@ Id3v2FrameMaker::Id3v2FrameMaker(Id3v2Frame &frame, std::uint8_t version, Diagno
         }
     }
 
+    // add a warning if we're writing the frame for an ID3v2 tag known not to support it
+    if (version <= 3 && Id3v2FrameIds::isOnlyId3v24Id(version < 3 ? Id3v2FrameIds::convertToLongId(m_frameId) : m_frameId)) {
+        diag.emplace_back(DiagLevel::Warning,
+            argsToString("The frame is only supported in ID3v2.4 and newer but version of the tag being written is ID3v2.", version,
+                ". The frame is written nevertheless but other tools might not be able to deal with it."),
+            context);
+    } else if (version > 3 && Id3v2FrameIds::isPreId3v24Id(m_frameId)) {
+        diag.emplace_back(DiagLevel::Warning,
+            argsToString("The frame is only supported in ID3v2.3 and older but version of the tag being written is ID3v2.", version,
+                ". The frame is written nevertheless but other tools might not be able to deal with it."),
+            context);
+    }
+
     // make actual data depending on the frame ID
     try {
         if (isTextFrame) {

id3/id3v2frameids.cpp

@@ -144,6 +144,44 @@ std::uint32_t convertToLongId(std::uint32_t id)
     }
 }
 
+/*!
+ * \brief Returns whether \a id is only supported in ID3v2.3.x and older and therefore can not be used in an ID3v2.4.x tag.
+ * \remarks
+ * - This function is intended to show warnings. Unknown IDs will be treated as supported everywhere.
+ * - Any short ID is obviously not ID3v2.4.x compatible. Only long IDs are considered here. Short IDs need to be converted to
+ *   long IDs before passing them to this function.
+ */
+bool isPreId3v24Id(uint32_t id)
+{
+    switch (id) {
+    case lYear:
+    case lOriginalYear:
+    case lRecordingDates:
+    case lDate:
+    case lTime:
+        return true;
+    default:
+        return false;
+    }
+}
+
+/*!
+ * \brief Returns whether \a id is only supported inID3v2.4.x and therefore can not be used in older versions.
+ * \remarks This function is intended to show warnings. Unknown IDs will be treated as supported everywhere.
+ */
+bool isOnlyId3v24Id(uint32_t id)
+{
+    switch (id) {
+    case lRecordingTime:
+    case lReleaseTime:
+    case lOriginalReleaseTime:
+    case lTaggingTime:
+        return true;
+    default:
+        return false;
+    }
+}
+
 } // namespace Id3v2FrameIds
 
 } // namespace TagParser

id3/id3v2frameids.h

@@ -78,6 +78,8 @@ enum KnownValue : std::uint32_t {
 
 TAG_PARSER_EXPORT std::uint32_t convertToShortId(std::uint32_t id);
 TAG_PARSER_EXPORT std::uint32_t convertToLongId(std::uint32_t id);
+TAG_PARSER_EXPORT bool isPreId3v24Id(std::uint32_t id);
+TAG_PARSER_EXPORT bool isOnlyId3v24Id(std::uint32_t id);
 
 /*!
  * \brief Returns an indication whether the specified \a id is a long frame id.