[#928] Set TZDIR if empty

[LeeMendelowitz]

This commit fixes #928 for me.

I start R --vanilla and then:

❯ R --vanilla
R version 4.0.3 (2020-10-10) -- "Bunny-Wunnies Freak Out"
Platform: x86_64-apple-darwin19.6.0 (64-bit)

r$> Sys.getenv("TZDIR")
[1] ""

r$> lubridate::dmy_hm("1 Sep 2020 1:00pm", tz="Africa/Blantyre")
[1] "2020-09-01 13:00:00 CAT"

r$> Sys.getenv("TZDIR")
[1] "/usr/share/zoneinfo"

session_info

r$> devtools::session_info()
─ Session info ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 setting  value
 version  R version 4.0.3 (2020-10-10)
 os       macOS Catalina 10.15.7
 system   x86_64, darwin19.6.0
 ui       unknown
 language (EN)
 collate  en_US.UTF-8
 ctype    en_US.UTF-8
 tz       America/New_York
 date     2020-11-19

─ Packages ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 package     * version    date       lib source
 assertthat    0.2.1      2019-03-21 [1] RSPM (R 4.0.3)
 backports     1.2.0      2020-11-02 [1] RSPM (R 4.0.3)
 callr         3.5.1      2020-10-13 [1] RSPM (R 4.0.3)
 cli           2.1.0      2020-10-12 [1] RSPM (R 4.0.3)
 crayon        1.3.4      2017-09-16 [1] RSPM (R 4.0.3)
 desc          1.2.0      2018-05-01 [1] RSPM (R 4.0.3)
 devtools      2.3.2      2020-09-18 [1] CRAN (R 4.0.3)
 digest        0.6.27     2020-10-24 [1] RSPM (R 4.0.3)
 ellipsis      0.3.1      2020-05-15 [1] RSPM (R 4.0.3)
 fansi         0.4.1      2020-01-08 [1] RSPM (R 4.0.3)
 fs            1.5.0      2020-07-31 [1] RSPM (R 4.0.3)
 generics      0.1.0      2020-10-31 [1] RSPM (R 4.0.3)
 glue          1.4.2      2020-08-27 [1] RSPM (R 4.0.3)
 lubridate     1.7.9.9001 2020-11-19 [1] local
 magrittr      1.5        2014-11-22 [1] RSPM (R 4.0.3)
 memoise       1.1.0      2017-04-21 [1] CRAN (R 4.0.3)
 pkgbuild      1.1.0      2020-07-13 [1] RSPM (R 4.0.3)
 pkgload       1.1.0      2020-05-29 [1] RSPM (R 4.0.3)
 prettyunits   1.1.1      2020-01-24 [1] RSPM (R 4.0.3)
 processx      3.4.4      2020-09-03 [1] RSPM (R 4.0.3)
 ps            1.4.0      2020-10-07 [1] RSPM (R 4.0.3)
 R6            2.5.0      2020-10-28 [1] RSPM (R 4.0.3)
 Rcpp          1.0.5      2020-07-06 [1] RSPM (R 4.0.3)
 remotes       2.2.0      2020-07-21 [1] CRAN (R 4.0.3)
 rlang         0.4.8      2020-10-08 [1] RSPM (R 4.0.3)
 rprojroot     1.3-2      2018-01-03 [1] RSPM (R 4.0.3)
 sessioninfo   1.1.1      2018-11-05 [1] CRAN (R 4.0.3)
 testthat      3.0.0      2020-10-31 [1] RSPM (R 4.0.3)
 usethis       1.6.3      2020-09-17 [1] CRAN (R 4.0.3)
 withr         2.3.0      2020-09-22 [1] RSPM (R 4.0.3)

[1] /usr/local/lib/R/4.0/site-library
[2] /usr/local/Cellar/r/4.0.3/lib/R/library

[LeeMendelowitz]

@vspinu This PR is a simple fix which resolves this issue for me. I based it off of your previous commits on this issue. Let me know if you have any questions

[vspinu]

I think my intent was to call Sys.timezone() on startup, but I paced it in the find_tzdir function. Shall we just call it unconditionally?

[LeeMendelowitz]

Sure! I just pushed that change.

[vspinu]

Thanks!