Fix `deepcopy`/`serialize` when used after `delete!`

[theogf]

Hey @andyferris !

It looks my deepcopy and serialize implementation have a bug. I wrongly assumed that indices.values == collect(indices). It is visibly not true and create undef references when using non isbits structure.

I used collect(indices) instead and took care of updating the tests accordingly.

(version patch is bumped as well)

[theogf]

Oh no there are actually more issues with the values of the Dictionary itself

[andyferris]

I see the problem.

What we can do is take a shortcut if holes == 0. Otherwise we need to use the kind of logic you see in rehash!. I suggest one of the two following options:

1. Just call rehash! if holes != 0 and then continue the current logic.
2. Iterate the tokens and collect the results if holes != 0

The disadvantage of the first one is it won't be thread safe when you have multiple readers (I'm not even sure it is safe under single-threaded concurrency).

Probably should go with the second with code like:

serialize_type(s, T, false)
if indices.holes == 0
    return serialize(s, ind.values)
else
    is = Vector{I}(undef, length(dict))
    @inbounds for t in tokens(dict)
        is[i] = ind.values[t]
    end
    return serialize(s, is)
end

It might be even better if we could stream out the indices in the second branch rather than collecting them in memory, but at least this is safe.

Will need equivalent code for dictionaries, and for deepcopy.

[theogf]

So I was thinking of an even more straightforward solution with dispatching deepcopy_internal on the Dictionary and collecting the values themself.

Something like

deepcopy(d::Dictionary{I,T}) where{I,T} = Dictionary{I,T}(deepcopy(collect(keys(d))), deepcopy(collect(d))) 

This way we just build a whole new Dictionary and avoid shenanigans ensuring that the holes and slots are consistent?

[theogf]

So I just implemented my proposal

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[theogf]

@andyferris Would you rather have me use your solution instead?

[0x0f0f0f]

@theogf news here?

[theogf]

Hi @andyferris, any update on this :) ?

[andyferris]

Sorry I have been smashed.

Correct is more important the fast, so lets merge this. Thanks @theogf

[andyferris]

https://github.com/JuliaRegistries/General/pull/69787