From Kurt@Horn|k @end|ng |rom wu@@c@@t  Tue Oct 11 16:44:13 2022
From: Kurt@Horn|k @end|ng |rom wu@@c@@t (Kurt Hornik)
Date: Tue, 11 Oct 2022 16:44:13 +0200
Subject: [Rd] Bug with `[<-.POSIXlt` on specific OSes
In-Reply-To: <CABzLhzxNNce6eEOnnv0fSpLRiZ70FC3-YadS2PeWOFSJfN6Zaw@mail.gmail.com>
References: <CABzLhzy0eTEAnb36raY5h_P=4+Dnm9uX0k0DB557zntD2qMLxg@mail.gmail.com>
 <CABzLhzxNNce6eEOnnv0fSpLRiZ70FC3-YadS2PeWOFSJfN6Zaw@mail.gmail.com>
Message-ID: <25413.33085.344041.49718@hornik.net>

>>>>> Davis Vaughan writes:

> I've got a bit more information about this one. It seems like it
> (only? not sure) appears when `TZ = "UTC"`, which is why I didn't see
> it before on my Mac, which defaults to `TZ = ""`. I think this is at
> least explainable by the fact that those "optional" fields aren't
> technically needed when the time zone is UTC.

Exactly.  Debugging `[<-.POSIlt` with

x <- as.POSIXlt(as.POSIXct("2013-01-31", tz = "America/Chicago"))
Sys.setenv(TZ = "UTC")
x[1] <- NA

shows we get into

    value <- unclass(as.POSIXlt(value))
    if (ici) {
        for (n in names(x)) names(x[[n]]) <- nms
    }
    for (n in names(x)) x[[n]][i] <- value[[n]]

where

Browse[2]> names(value)
[1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"  "isdst"
Browse[2]> names(x)
 [1] "sec"    "min"    "hour"   "mday"   "mon"    "year"   "wday"   "yday"  
 [9] "isdst"  "zone"   "gmtoff"

Without having looked at the code, the docs say

     ?zone? (Optional.) The abbreviation for the time zone in force at
          that time: ?""? if unknown (but ?""? might also be used for
          UTC).

     ?gmtoff? (Optional.) The offset in seconds from GMT: positive
          values are East of the meridian.  Usually ?NA? if unknown,
          but ?0? could mean unknown.

so perhaps we should fill with the values for the unknown case?

-k

> I can reproduce this now on my personal Mac:

> ```

> x <- as.POSIXlt(as.POSIXct("2013-01-31", tz = "America/Chicago"))

> Sys.setenv(TZ = "")

> x[1] <- NA

> x

> #> [1] NA


> x <- as.POSIXlt(as.POSIXct("2013-01-31", tz = "America/Chicago"))

> Sys.setenv(TZ = "America/New_York")

> x[1] <- NA

> x

> #> [1] NA


> x <- as.POSIXlt(as.POSIXct("2013-01-31", tz = "America/Chicago"))

> Sys.setenv(TZ = "UTC")

> x[1] <- NA
> #> Error in x[[n]][i] <- value[[n]] : replacement has length zero

> x

> #> [1] "2013-01-31 CST"
> ```

> Here are `sessionInfo()` and `Sys.getenv("TZ")` outputs for 3 GitHub
> Actions platforms where the bug exists (note they all set `TZ = "UTC"`!):

> Linux:

> ```

>> sessionInfo()

> R version 4.2.1 (2022-06-23)

> Platform: x86_64-pc-linux-gnu (64-bit)

> Running under: Ubuntu 18.04.6 LTS


> Matrix products: default

> BLAS:   /usr/lib/x86_64-linux-gnu/openblas/libblas.so.3

> LAPACK: /usr/lib/x86_64-linux-gnu/libopenblasp-r0.2.20.so


> locale:

>  [1] LC_CTYPE=C.UTF-8       LC_NUMERIC=C           LC_TIME=C.UTF-8

>  [4] LC_COLLATE=C.UTF-8     LC_MONETARY=C.UTF-8    LC_MESSAGES=C.UTF-8

>  [7] LC_PAPER=C.UTF-8       LC_NAME=C              LC_ADDRESS=C

> [10] LC_TELEPHONE=C         LC_MEASUREMENT=C.UTF-8 LC_IDENTIFICATION=C


> attached base packages:

> [1] stats     graphics  grDevices utils     datasets  methods   base


> loaded via a namespace (and not attached):

> [1] compiler_4.2.1


>> Sys.getenv("TZ")

> [1] "UTC"
> ```

> Mac:

> ```

>> sessionInfo()

> R version 4.2.1 (2022-06-23)

> Platform: x86_64-apple-darwin17.0 (64-bit)

> Running under: macOS Big Sur ... 10.16


> Matrix products: default

> BLAS:
> /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRblas.0.dylib

> LAPACK:
> /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRlapack.dylib


> locale:

> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8


> attached base packages:

> [1] stats     graphics  grDevices utils     datasets  methods   base


> loaded via a namespace (and not attached):

> [1] compiler_4.2.1


>> Sys.getenv("TZ")

> [1] "UTC"
> ```

> Windows:
> This is the best I can get you, sorry (remote worker issues), but note that
> it does also say `tz UTC` like the others.

> ```
> version R version 4.2.1 (2022-06-23 ucrt)
> os Windows Server x64 (build 20348)
> system x86_64, mingw32
> ui RTerm
> language (EN)
> collate English_United States.utf8
> ctype English_United States.utf8
> tz UTC
> date 2022-10-11
> ```

> And here is my Mac where the bug doesn't show up by default because `TZ =
> ""`:

> ```

>> sessionInfo()

> R version 4.2.1 (2022-06-23)

> Platform: x86_64-apple-darwin17.0 (64-bit)

> Running under: macOS Big Sur ... 10.16


> Matrix products: default

> BLAS:
> /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRblas.0.dylib

> LAPACK:
> /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRlapack.dylib


> locale:

> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8


> attached base packages:

> [1] stats     graphics  grDevices utils     datasets  methods   base


> loaded via a namespace (and not attached):

> [1] compiler_4.2.1


>> Sys.getenv("TZ")

> [1] ""


>> Sys.timezone()

> [1] "America/New_York"
> ```

> -Davis


> On Thu, Oct 6, 2022 at 9:33 AM Davis Vaughan <davis at rstudio.com> wrote:

>> Hi all,
>> 
>> I have found another POSIXlt bug while I've been fiddling around with it.
>> This one only appears on specific OSes, because it has to do with the fact
>> that the `gmtoff` field is optional, and isn't always used on all OSes. It
>> also doesn't seem to be specific to r-devel, I think it has been there
>> awhile.
>> 
>> Here is the bug:
>> 
>> ```
>> x <- as.POSIXlt(as.POSIXct("2013-01-31", tz = "America/Chicago"))
>> 
>> # Oh no!
>> x[1] <- NA
>> #> Error in x[[n]][i] <- value[[n]] : replacement has length zero
>> ```
>> 
>> If you look at the objects, you can see that `x` has a `gmtoff` field, but
>> `NA` (when converted to POSIXlt, which is what `[<-.POSIXlt` does) does not:
>> 
>> ```
>> unclass(x)
>> #> $sec
>> #> [1] 0
>> #>
>> #> $min
>> #> [1] 0
>> #>
>> #> $hour
>> #> [1] 0
>> #>
>> #> $mday
>> #> [1] 31
>> #>
>> #> $mon
>> #> [1] 0
>> #>
>> #> $year
>> #> [1] 113
>> #>
>> #> $wday
>> #> [1] 4
>> #>
>> #> $yday
>> #> [1] 30
>> #>
>> #> $isdst
>> #> [1] 0
>> #>
>> #> $zone
>> #> [1] "CST"
>> #>
>> #> $gmtoff
>> #> [1] -21600
>> #>
>> #> attr(,"tzone")
>> #> [1] "America/Chicago" "CST"             "CDT"
>> 
>> unclass(as.POSIXlt(NA))
>> #> $sec
>> #> [1] NA
>> #>
>> #> $min
>> #> [1] NA
>> #>
>> #> $hour
>> #> [1] NA
>> #>
>> #> $mday
>> #> [1] NA
>> #>
>> #> $mon
>> #> [1] NA
>> #>
>> #> $year
>> #> [1] NA
>> #>
>> #> $wday
>> #> [1] NA
>> #>
>> #> $yday
>> #> [1] NA
>> #>
>> #> $isdst
>> #> [1] -1
>> #>
>> #> attr(,"tzone")
>> #> [1] "UTC"
>> ```
>> 
>> The problem seems to be that `[<-.POSIXlt` assumes that if the field was
>> there in `x` then it must also be there in `value`:
>> 
>> https://github.com/wch/r-source/blob/e10a971dee6a0ab851279c183cc21954d66b3be4/src/library/base/R/datetime.R#L1303-L1304
>> 
>> But this isn't the case for the `NA` value that was converted to POSIXlt.
>> 
>> I can't reproduce this on my personal Mac, but it affects the Linux, Mac,
>> and Windows machines we use for the lubridate CI checks through GitHub
>> Actions.
>> 
>> Thanks,
>> Davis
>> 

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[Rd] Bug with `[<-.POSIXlt` on specific OSes
Kurt Hornik