Add convenience functions for overriding ABMs, LBMs and entities

[sfence]

• Extend Lua API for mod and game creators.
• It adds override Lua functions for ABM, LBM, and entities.
• This should fix Add minetest.override_entity() #6909 at least.
• This also adds some checks to generate an error message when some mod tries to call some functions like register_node, register_lbm, etc after mod loading is finished.

To do

This PR is a Ready for Review

• Get feedback.
• Apply feedback.
• Add some tests, probably to devtest unittests.
• Check if biome definition and/or similar definitions can be overridden as well ( Ability to (partially) override definitions of existing biomes after they have been registered #9161 )

How to test

Run detest game. minetest.override_entity is tested in unittests. Test for minetest.override_abm and minetest.override_lbm can be done by placing nodes testabms:override and testlbms:onload_change from mods testabms and testlbms.

[Zughy]

(only entities are in the roadmap, but I guess it won't hurt 🤷‍♀️ ; unsubscribing)

[grorp]

• Adding error messages about calling registration functions after load time could go into a dedicated bugfix PR.

• At least entity definitions are definitely already overridable by modifying minetest.registered_entities:

  https://github.com/minetest/minetest/blob/32e492837cbf286aeb91b4b63ecf3c890c71a1bc/doc/lua_api.md?plain=1#L6992-L6996

  This even works after load time AFAIK. So this PR only makes it more convenient.

• Shouldn't overriding ABMs and LBMs by modifying minetest.registered_abms/minetest.registered_lbms at load time already work as well?

Of course, that doesn't make this PR invalid. It's more convenient to have API functions for this purpose.

[kromka-chleba]

It adds override Lua functions for ABM, LBM, and entities.

I guess this resolves my issue? #13112
TL;DR Will this let me unregister and change ABMs/LBMs?

[grorp]

I guess this resolves my issue? #13112
TL;DR Will this let me unregister and change ABMs/LBMs?

It doesn't allow doing that "on the fly", so it probably doesn't resolve your issue.

[sfence]

@kromka-chleba

This only allows a change of abm/lbm at loading time. After mods are loaded, the Lua tables registered_abm and registered_lbm are loaded by C++ and converted to C++ class/structures which are used by the engine to proceed abm and lbm calls.

Supporting dynamic changing of lbm/abm during the game running will be more difficult to implement.

[sfence]

• Adding error messages about calling registration functions after load time could go into a dedicated bugfix PR.

If this PR is closed without merging, I can create a specific PR for this. But because it takes time to merge PR, I would like to keep it here, instead of creating a separate PR and setting this PR to be blocked/waiting for it to be merged.

• At least entity definitions are definitely already overridable by modifying minetest.registered_entities:
  https://github.com/minetest/minetest/blob/32e492837cbf286aeb91b4b63ecf3c890c71a1bc/doc/lua_api.md?plain=1#L6992-L6996

You are right. But in this way, with added error message it will be a more foolproof/error-proof way to override. This is too reason why do not create separate bugfix PR, I think.

This even works after load time AFAIK. So this PR only makes it more convenient.

Yes, but at least adding override_entity is in the roadmap. If actual solution is enough, Issue #6909 should in the closed state.

• Shouldn't overriding ABMs and LBMs by modifying minetest.registered_abms/minetest.registered_lbms at load time already work as well?

Yes, it is possible. But you have to go through register_abms or registered_lbms tables manually in every situation where you want to override abm or lbm.

Of course, that doesn't make this PR invalid. It's more convenient to have API functions for this purpose.

[sfence]

Overriding of biomes will require changes and method adding in C++, so I will not implement it here. It should be a separate PR.

[sfence]

I have added the possibility of testing override functionality.

So, this is now prepared for review.

[lhofhansl]

I like the idea. Nice tests!
I find myself not in a position to really review it. It looks right, and nothing obviously bad.

Once question, could one also do this with a helper mod that implements override_abm? It seems all this does it looking through the list of registered ABMs/LBMs and then modifies them.

[sfence]

I like the idea. Nice tests! I find myself not in a position to really review it. It looks right, and nothing obviously bad.

Once question, could one also do this with a helper mod that implements override_abm? It seems all this does it looking through the list of registered ABMs/LBMs and then modifies them.

Yes, all of this can be done by external mod with an exception for checking the is_mods_loaded field.
I have added and documented an optional new field name for ABM. It is checked in register_abm calls, if is provided, and allows ABM to be overridden.
It cannot be a required field because of backward compatibility.

But, my opinion is that It will be better to have this as part of the official modding API.

[Zughy]

@sfence more rebase needed (then please remove the label when you're done)