[Rd] Date method of as.POSIXct does not respect tz

[Martin Maechler]

>>>>> Martin Maechler 
>>>>>     on Fri, 23 Sep 2022 11:04:12 +0200 writes:

>>>>> Kurt Hornik 
>>>>>     on Fri, 23 Sep 2022 09:57:49 +0200 writes:

>>>>> Martin Maechler writes:

>     > Currently in R-devel,
> 
>     R> as.POSIXlt.Date
>     > function (x, ...) 
>     > {
>     >    if (any((y <- unclass(x)) > .Machine$integer.max, na.rm = TRUE)) 
>     >         as.POSIXlt(.POSIXct(y * 86400), tz = "UTC")
>     >    else .Internal(Date2POSIXlt(x))
>     > }
> 
>     R> as.POSIXct.Date
>     > function (x, ...) 
>     > .POSIXct(unclass(x) * 86400)
> 
>     > Adding tz to the latter is easy, and the former could do the if() part
>     > also with a given tz without needing to change the .Internal?
> 
> Genau!  Even more elegantly than I first thought when I wrote
> "post-processing":
> 
> The following even adds internal consistency inside as.POSIXlt.Date() :
> 
> as.POSIXlt.Date <- function(x, tz = "UTC", ...) {
>     as.POSIXlt(if(any((y <- unclass(x)) > .Machine$integer.max, na.rm = TRUE))
>                    .POSIXct(y * 86400)
>                else
>                    .Internal(Date2POSIXlt(x))
>              , tz = tz)
> }
> 
> because now, tz is even *formally* treated the same in both
> cases (whereas previously it only appeared visually in one case).
> 
> So probably, another reason to go there.
> Note that I also think we'd keep the    tz = "UTZ"
> default argument, even when the
> other  as.POSIX[cl]t() methods have 'tz = ""'

Hmm, good plan, but not working for the (more important) second
branch:

   as.POSIXlt(<POSIXlt>, tz = "..")

immediately returns the first argument without ever looking if
there are further arguments, in this case 'tz'..

--> we would also have to slightly change  as.POSIXlt.default(x)
such that it obeyed a 'tz = ".."'  in the case of x being
"POSIXlt".
Almost surely this will break some code which had relied on the
current -- a bit surpristing to me -- behavior.

Well,... I think we *should* want the above {setting a "tz"} for
POSIXlt to work.

Martin