table.copy removes metatables

[immagiov4]

Luanti version

5.10

Operating system and version

Windows 11

CPU model

No response

GPU model

No response

Active renderer

No response

Summary

The title says it all I guess: table.copy doesn't keep metatables into copied tables.

Steps to reproduce

meta = {metavalue = "we_like_diversity"}

t = {value = "we_lack_diversity"}
setmetatable(t, meta)
core.chat_send_all(dump(getmetatable(t)))

final_t = table.copy(t)
core.chat_send_all(dump(getmetatable(final_t)))

[SmallJoker]

Marked as feature request because I only intended to duplicate the data (key/values) of a table when I implemented the first version of table.copy. Metatables are an after-thought. Copying that (recursively) to the new table shouldn't be too complicated.

[appgurueu]

Metatables are an after-thought. Copying that (recursively) to the new table shouldn't be too complicated.

I don't think the metatable should generally be copied, both for performance and correctness reasons (think vector.is being false for a copied vector because you copied the vector "class" as well). It should just be restored instead.

Short term I think we should just add a boolean param defaulting to false that indicates whether to preserve metatables, probably with a notice that we plan to make this the default eventually (though technically the fact that metatables are stripped is not something we guarantee in our docs).

Longer term, we can provide a recursive core.strip_metatables for those who want that, but e.g. vectors losing their metatables through copying is not a useful default. Cases where you want to strip metatables are much rarer.