Why is the warning "[minecraft/ClientRecipeBook]: Unknown recipe category" normal and unavoidable?

[Warren Tode]

I am new to modding in Forge, but I've played around with datapacks for quite some time. So I'm fairly comfortable with the whole "mess around and find out" when it comes to Json, but not so much with Java. All month I've been trying to make the warning "[minecraft/ClientRecipeBook]: Unknown recipe category" go away while trying to set up a custom shaped recipe for a custom furnace and not once did I think to actually test it to see if it worked, until I decided to look up what this warning actually meant. I found this old thread here, 

where it's stated that the warning is normal and unavoidable. So I went back and tested my recipes and turns out they work just fine. I'm super thrilled about the fact my Json recipe files are readable and working, but now I'm wondering why this warning is a normal thing and what exactly does it mean? Is it the same sort of thing that pops up in the IDE telling me that my custom recipe type listed in my custom Json file is unknown?

[ChampionAsh5357]

3 hours ago, Warren Tode said:

but now I'm wondering why this warning is a normal thing and what exactly does it mean?

So, it was a normal thing for a while. The error comes from the recipe book as it tries to determine which category the recipe should appear in within the recipe book for your custom recipe type. As most people generally don't use the recipe book for their custom recipes types, it typically isn't an issue to ignore the warning. As of 8028, you can now create your own categories and add to existing ones.

3 hours ago, Warren Tode said:

Is it the same sort of thing that pops up in the IDE telling me that my custom recipe type listed in my custom Json file is unknown?

No, in that case, that usually indicates that the recipe serializer is not registered. For reference, the recipe type and recipe serializer are different. The recipe serializer is what's used to read the JSON file while the recipe type indicates the category the recipe is for. For example, you can have a custom recipe serializer with a crafting recipe type such that crafting tables are able to use the recipes from your serializer.

[Warren Tode]

2 hours ago, ChampionAsh5357 said:

So, it was a normal thing for a while. The error comes from the recipe book as it tries to determine which category the recipe should appear in within the recipe book for your custom recipe type. As most people generally don't use the recipe book for their custom recipes types, it typically isn't an issue to ignore the warning. As of 8028, you can now create your own categories and add to existing ones.

No, in that case, that usually indicates that the recipe serializer is not registered. For reference, the recipe type and recipe serializer are different. The recipe serializer is what's used to read the JSON file while the recipe type indicates the category the recipe is for. For example, you can have a custom recipe serializer with a crafting recipe type such that crafting tables are able to use the recipes from your serializer.

Okay, this explains so much! And thank you for taking the time to go into detail on that for me. I now understand why the Json recipe error went away and I get why this other thing is still happening and how it's not a crisis. It's really cool to know that custom recipe book categories are an option now, but one thing at a time. lol There's so much to learn and tinker with over here. I'll bookmark your link for later. I feel like a kid in a candy store. Again, thank you.