Armour trim materials and patterns can be inlined in the NBT for item stacks.

Steps to reproduce:

1. Open any world (ideally one without any data packs to showcase the bug better)
2. Apply the resource pack present in this bug report: Armour Trims Bug Resource Pack.zip
3. Give yourself the following item stack and wear it (I expanded it to make it easier to read)

   minecraft:leather_chestplate{
   	Trim: {
   		material: {
   			asset_name: "test",
   			description: {
   				text: "Test Material",
   				color: "#66B24C"
   			},
   			ingredient: "minecraft:air",
   			item_model_index: 0.15f
   		},
   		pattern: {
   			asset_id: "bug:test",
   			description: {
   				text: "Test Armour Trim"
   			},
   			template_item: "minecraft:air"
   		}
   	}
   }

1. Notice how the armour trim is applied

Code analysis

In the TrimMaterial and TrimPattern records the CODEC field calls RegistryFileCodec::create(ResourceKey<? extends Registry<E>>, Codec<E>), which creates a new instance of RegistryFileCodec with allowInline set to true. See the copied bit for TrimMaterial.

public record TrimMaterial(String assetName, Holder<Item> ingredient, float itemModelIndex, Map<ArmorMaterials, String> overrideArmorMaterials, Component description) {
    // ...
    public static final Codec<Holder<TrimMaterial>> CODEC = RegistryFileCodec.create(Registries.TRIM_MATERIAL, DIRECT_CODEC);
    // ...
}

This can be fixed by calling the method overload RegistryFileCodec::create(ResourceKey<? extends Registry<E>>, Codec<E>, boolean) instead, with the boolean set to false and thereby disallowing inline entries.