slices.Compact(s) // modified slice in the return value is ignored
s = slices.Compact(s) // s now points to the new changed slice
s := slices.Compact(s) // s already exists, this is not valid Go syntax.
slices.Delete(s, …) // modified slice in the return value is ignored
s = slices.Delete(s, …) // s now points to the new changed slice
As that's the case it's indeed hard to defend it. Data structure-wise it still kind of makes sense since as you mentioned the slice metadata is changed, but it basically making the old slice invalid is rather annoying.
For the := example sure, it's a bit far fetched example and likely would not pass any code review, but there are cases where shadowing is indeed valid. So is the `s := slices.Compact(s)` in this example not working as expected then?
EDIT: looking at another reply to the parent the := being broken likely is trying to point that using := also modifies the slice and thus the original slice is broken when one tries to use it in the original scope. That's really bad practice, but true indeed.