fix(uverse): overlap handling in append/copy for slice-backed lists

[omarsy]

• Make append overlap-safe for list-backed slices by using directional copy (backward when dst starts after src).
• Make copy overlap-safe for slice-to-slice by using directional copy when src/dst share the same backing array.

[Gno2D2]

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[Davphla]

Fix works great, all comments are refacto / nitpick

[Davphla]

This comment can be simplified

[Davphla]

This double duplicate loop can be simplified either by doing a sub helper function, or something like that:

step := 1
start := 0
if overlap && dstStart > srcStart {
    step = -1
    start = arg1Length - 1
}
for i := start; i >= 0 && i < arg1Length; i += step {
    oldElem := list[dstStart+i]
    newElem := arg1Base.List[arg1Offset+i].unrefCopy(m.Alloc, m.Store)
    list[dstStart+i] = newElem
    m.Realm.DidUpdate(
        arg0Base,
        oldElem.GetFirstObject(m.Store),
        newElem.GetFirstObject(m.Store),
    )
}

I think it would be much easier to read

[omarsy]

nice suggestion ^^

[Davphla]

same for this one

[Davphla]

It's missing the case where it append to itself (fixed by that PR)

[omarsy]

WDYM, Can you give me an example ?

[Davphla]

Example:

r4 := append(s4[:1], s4...)

It's not essential to add tbh