Explain backup tags (#1)

common/src/main/java/com/viaversion/viaversion/protocols/protocol1_20_5to1_20_3/rewriter/BlockItemPacketRewriter1_20_5.java

@@ -509,6 +509,15 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
         return item;
     }
 
+    private int unmappedItemId(final String name) {
+        return protocol.getMappingData().itemId(name);
+    }
+
+    private int toMappedItemId(final String name) {
+        final int unmappedId = unmappedItemId(name);
+        return unmappedId != -1 ? protocol.getMappingData().getNewItemId(unmappedId) : -1;
+    }
+
     private void restoreFromBackupTag(final CompoundTag backupTag, final StructuredDataContainer data) {
         final CompoundTag instrument = backupTag.getCompoundTag("instrument");
         if (instrument != null) {
@@ -586,7 +595,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
             final CompoundTag soundEventCompound = (CompoundTag) soundEventTag;
             final StringTag identifier = soundEventCompound.getStringTag("identifier");
             if (identifier == null) {
-                return; // Nothing we can do about
+                return;
             }
             soundEvent = Holder.of(new SoundEvent(
                 identifier.getValue(),
@@ -594,7 +603,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
                     soundEventCompound.getFloat("fixed_range") : null
             ));
         } else {
-            return; // Nothing we can do about
+            return;
         }
         data.set(StructuredDataKey.INSTRUMENT, Holder.of(new Instrument(soundEvent, useDuration, range)));
     }
@@ -613,7 +622,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
         for (final CompoundTag effect : possibleEffectsTag) {
             final CompoundTag potionEffectTag = effect.getCompoundTag("effect");
             if (potionEffectTag == null) {
-                continue; // Nothing we can do about
+                continue;
             }
             possibleEffects.add(new FoodEffect(
                 new PotionEffect(
@@ -643,7 +652,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
                 }
             }
             if (blocks == null) {
-                continue; // Nothing we can do about
+                continue;
             }
             rules.add(new ToolRule(
                 blocks,
@@ -663,7 +672,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
         for (final CompoundTag tag : bannerPatterns) {
             final CompoundTag patternTag = tag.getCompoundTag("pattern");
             if (patternTag == null) {
-                continue; // Nothing we can do about
+                continue;
             }
             final String assetId = patternTag.getString("asset_id");
             final String translationKey = patternTag.getString("translation_key");
@@ -673,15 +682,6 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
         data.set(StructuredDataKey.BANNER_PATTERNS, patternLayer.toArray(new BannerPatternLayer[0]));
     }
 
-    private int unmappedItemId(final String name) {
-        return protocol.getMappingData().itemId(name);
-    }
-
-    private int toMappedItemId(final String name) {
-        final int unmappedId = unmappedItemId(name);
-        return unmappedId != -1 ? protocol.getMappingData().getNewItemId(unmappedId) : -1;
-    }
-
     private AdventureModePredicate updateBlockPredicates(final ListTag<StringTag> tag, final boolean showInTooltip) {
         final BlockPredicate[] predicates = tag.stream()
             .map(StringTag::getValue)

common/src/main/java/com/viaversion/viaversion/protocols/protocol1_20_5to1_20_3/rewriter/StructuredDataConverter.java

@@ -79,9 +79,13 @@ public final class StructuredDataConverter {
     static final int HIDE_DYE_COLOR = 1 << 6;
     static final int HIDE_ARMOR_TRIM = 1 << 7;
 
-    // Can't do nicely
+    // Store invalid/inconvertible data in the backup tag and later
+    // restore it when converting back to the original version
     private static final String BACKUP_TAG_KEY = "VV|DataComponents";
-    private static final String ITEM_BACKUP_TAG_KEY = "VV|id";
+
+    // Store item ids separately to avoid copying whole data tree
+    // just for the item id
+    private static final String ITEM_BACKUP_TAG_KEY = "VV|Id";
 
     private final Map<StructuredDataKey<?>, DataConverter<?>> rewriters = new Reference2ObjectOpenHashMap<>();
     private final boolean backupInconvertibleData;
@@ -301,8 +305,8 @@ public final class StructuredDataConverter {
             for (final int id : data.itemIds()) {
                 final String name = toMappedItemName(id);
                 if (name.isEmpty()) {
-                    // Backup whole data if one of the sherds is inconvertible
-                    // Since we don't want to break the order of the sherds
+                    // Backup whole data if one of the entries is inconvertible
+                    // Since we don't want to break the order of the entries
                     if (backupInconvertibleData && originalSherds == null) {
                         originalSherds = new IntArrayTag(data.itemIds());
                     }
@@ -410,8 +414,8 @@ public final class StructuredDataConverter {
         register(StructuredDataKey.BANNER_PATTERNS, (data, tag) -> {
             final ListTag<CompoundTag> originalPatterns = new ListTag<>(CompoundTag.class);
             if (backupInconvertibleData) {
-                // Backup whole data if one of the patterns is inconvertible
-                // Since we don't want to break the order of the patterns
+                // Backup whole data if one of the entries is inconvertible
+                // Since we don't want to break the order of the entries
                 if (Arrays.stream(data).anyMatch(layer -> layer.pattern().isDirect())) {
                     for (final BannerPatternLayer layer : data) {
                         final CompoundTag layerTag = new CompoundTag();
@@ -645,6 +649,7 @@ public final class StructuredDataConverter {
         return backupTag;
     }
 
+    // Check if item name could be mapped, if not, locate original/backup item id and use it
     static int removeItemBackupTag(final CompoundTag tag, final int unmappedId) {
         if (unmappedId != -1) {
             return unmappedId;
@@ -674,8 +679,10 @@ public final class StructuredDataConverter {
             } else {
                 for (final int id : holders.ids()) {
                     final String name = toMappedItemName(id);
-                    if (backupInconvertibleData && name.isEmpty()) {
-                        // TODO HANDLE
+                    if (name.isEmpty()) {
+                        if (backupInconvertibleData) {
+                            // TODO Backup
+                        }
                         continue;
                     }
                     predicatedListTag.add(serializeBlockPredicate(predicate, name));