setDT not always sets ".internal.selfref"

[rikivillalba]

Reading #6862 I found this behaviour:

ds = copy(datasets::iris)
x = setDT(get("ds"))
attr(ds, ".internal.selfref")   # <pointer...>

ds = copy(datasets::iris)
x = setDT(get0("ds"))            # note get0
attr(ds, ".internal.selfref")    # NULL

Both ds's set as data.table's but in the second form, ds lacks selfref.
AFAIK setalloccol() is shallow copying ds, but then setDT fails to reassign it to the symbol ds because not recognizing 'get0' bindimg.
Arguably there is no easy way to detect the binding for every possible call that returns a data.table bound to a symbol, so I think setDT should warn when it is unable to assign it back -if a shallow copy is made-. or if ds lacks selfref before returning.
However, x does have it, and thus identical(ds, x) fails in second case.
Related perhaps #6754

[MichaelChirico]

I think in this case we can continue the kludge pretty easily -- there's already logic for get(), it was just written before get0() existed (? or at least was more well-known):

data.table/R/data.table.R

Line 2990 in 3afc750

} else if (name %iscall% "get") { # #6725

Note also #6702

[venom1204]

Hi @MichaelChirico @rikivillalba

Can I work on this issue .
As suggested by Michael, I'll update the existing logic in setDT() to handle get0() similarly to get():

else if (name %iscall% "get" || name %iscall% "get0")

Thanks!

[MichaelChirico]

Let's get #6802 finished first, since it is likely to generate conflict with that change