Modules: Can I override mixins?

[hookstar]

I am trying to override a mixin and the override will not take on build. Is there something special about mixins that I am unaware of on how they work or process?

Thanks.

[zach2good]

Do you have an example so we can reproduce the problem? Have you looked at how mixins are loaded or fired when compared to regular Lua functions, or the Lua cache (the xi object)?

If you searched for "mixins" you would have seen this issue where I explained in detail exactly how they work: #4493

As with all things modules, if you're having trouble getting them to load normally or to hot-reload them, you can attach the logic you want to change to something on the xi object and override that, instead of the plumbing of the mixins themselves.

[zach2good]

Relevant bits for how modules are applied:
https://github.com/LandSandBoat/server/blob/base/src/map/utils/moduleutils.cpp#L260
https://github.com/LandSandBoat/server/blob/base/src/map/lua/luautils.cpp#L560

[hookstar]

Thanks, I searched mixins but 13 pages in decided to write this. As always, you're the best! Appreciate the links and explanation.

[hookstar]

Maybe this next question would be better targeted, suppose I just want to overwrite an entire file, is using a module to do that the best course of action?

[WinterSolstice8]

I don't think you need return g_mixins.families.flan at all due to how modules work (they replace functions wholesale). Just return m instead

[hookstar]

ok thank you

[hookstar]

Yea i dont know what I am doing wrong - it doesnt seem to want to apply the module

[zach2good]

To understand why this doesn't work, you have to understand a) how Lua loads and caches items requested through require, b) how we load and cache things, and in what order, and c) how mixins are loaded and applied.

(in the old style of requiring IDs, but is a good example of the point I'm explaining)

local ID = require("scripts/zones/Northern_San_dOria/IDs")

https://www.lua.org/pil/8.1.html

TLDR; require loads a file into an internal cache based on the path string you've looked it up with, and then returns that object from the cache if you ask for it again. This internal cache is the package.loaded object. You can clear things out of the cache by setting entries in there to nil. We do this in some utils like !reloadquest and xi.module.modifyInteractionEntry.

Now, relevant to mixins:

-----------------------------------
-- Area: Middle Delkfutt's Tower
--   NM: Ogygos
-----------------------------------
mixins = { require('scripts/mixins/job_special') }
-----------------------------------
local entity = {}

entity.onMobDeath = function(mob, player, optParams)
    xi.hunts.checkHunt(mob, player, 339)
end

return entity

When job_special is loaded, it puts the contents of that script (a tble of a bunch of functions that add listeners to a mob) into g_mixins.job_special, and it returns it. This returned table is THEN CACHED into package.loaded. In Ogygos script that table we've just loaded is dumped into a GLOBAL object: mixins. When we're loading things in core we are keeping an eye our for if this global mixin object is present after we load a mob/npc, and then executing whatever is in that object.

server/src/map/utils/zoneutils.cpp

Line 651 in 20d547a

luautils::ApplyMixins(PMob);

Modules work by building up the list of overrides and strings for the scripts we're targeting, and continually trying to apply them every time we load a Lua file (mob, npc, item, whatever.). Like I mentioned in #4493, mixins are the last holdout of the pre-Sol-refactor system where things don't run through CacheLuaObjectFromFile (the central point of our Lua caching system).

Why doesn't my override work?

As mentioned, an override will only apply when a file is loaded through CacheLuaObjectFromFile and it makes it all the way to the end of that function, where the last point in that function is moduleutils::TryApplyLuaModules();.

Mixins aren't loaded through CacheLuaObjectFromFile. Therefore, overrides won't be applied to them.

If we added the folder https://github.com/LandSandBoat/server/tree/base/scripts/mixins to the global "you should load everything in these folders" list, then those files would get pumped through CacheLuaObjectFromFile and then added to our internal Lua cache, and then they'd be available for overriding with modules.

But have you caught why we haven't done this yet?

We load mobs before we load and apply mixins.

mixins = { require('scripts/mixins/job_special') }

We've cached the mixin object. This is before the point where we'd override things. Therefore, any overrides applied to job_special won't apply to any file that has cached the object with require.

All of this is what I was explaining in the issue and writeup I linked you. This isn't a difficult problem to solve, but it is non-trivial.