Don't try to modify an immutable map

Author: onebeastchris

core/src/main/java/org/geysermc/geyser/registry/populator/CustomItemRegistryPopulator.java

@@ -464,6 +464,14 @@ private static void setupBasicItemInfo(CustomItemDefinition definition, DataComp
         // This can be missing if a non-vanilla item didn't specify a max stack size, or if a component patch removed the component. In that case vanilla Minecraft defaults to 1
         int stackSize = components.getOrDefault(DataComponentTypes.MAX_STACK_SIZE, 1);
 
+        // Hack for v1 compat: Allow e.g. carved pumpkins to continue working as a base
+        if (stackSize > 1 && definition instanceof GeyserCustomItemDefinition customItemDefinition && customItemDefinition.isOldConvertedItem()) {
+            Equippable equippable = components.get(DataComponentTypes.EQUIPPABLE);
+            if (equippable != null) {
+                stackSize = 1;
+            }
+        }
+
         itemProperties.putInt("max_stack_size", stackSize);
 
         // Ignore durability if the item's predicates requires that it be unbreakable

core/src/main/java/org/geysermc/geyser/registry/populator/custom/CustomItemContext.java

@@ -101,10 +101,8 @@ private static DataComponents checkComponents(CustomItemDefinition definition, I
         int maxDamage = components.getOrDefault(DataComponentTypes.MAX_DAMAGE, 0);
 
         if (components.get(DataComponentTypes.EQUIPPABLE) != null && stackSize > 1) {
-            // V1 compat: forcibly set max stack size to one
-            if (definition instanceof GeyserCustomItemDefinition geyserCustomItemDefinition && geyserCustomItemDefinition.isOldConvertedItem()) {
-                components.put(DataComponentTypes.MAX_STACK_SIZE, 1);
-            } else {
+            // V1 compat: Allow old items to function; we'll patch in stack size to one later
+            if (!(definition instanceof GeyserCustomItemDefinition)) {
                 throw new InvalidItemComponentsException("Bedrock doesn't support equippable items with a stack size above 1");
             }
         } else if (stackSize > 1 && maxDamage > 0) {