failing 'rstan' installation due to timezone issue?!

[boegel]

During the installation of R-4.0.0-foss-2020a.eb in the 2021.03 version of the software layer, the installation of rstan is failing with:

** R
** inst
** byte-compile and prepare package for lazy loading
Error in as.POSIXlt.character(x, tz, ...) :
  character string is not in a standard unambiguous format
Error: unable to load R code in package rstan
Execution halted
ERROR: lazy loading failed for package rstan

Others have reported this issue with rstan too, see stan-dev/rstan#612.

The problem is easy to reproduce manually when starting R:

$ R
> as.POSIXct("1970-01-01 00:00.00 UTC")
Error in as.POSIXlt.character(x, tz, ...) :
  character string is not in a standard unambiguous format

Workaround in R:

> as.POSIXct("1970-01-01 00:00.00 UTC", tz='UTC')
[1] "1970-01-01 UTC"

Workaround using $TZ:

$ TZ=UTC R
> as.POSIXct("1970-01-01 00:00.00 UTC")
[1] "1970-01-01 UTC"

I worked around this in 86e5ca9 by setting $TZ to UTC when installing R.

[boegel]

This is related to not having /etc/localtime anymore in the 2021.03 compat layer, while it is there in 2020.12:

$ cat /cvmfs/pilot.eessi-hpc.org/2020.12/compat/linux/x86_64/etc/localtime
TZif2-00TZif2-00
<-00>0

The problem can be fixed by symlinking the missing file to the host:

ln -s /etc/localtime /cvmfs/pilot.eessi-hpc.org/2021.03/compat/linux/x86_64/etc/localtime

[bedroge]

This has been solved in EESSI/compatibility-layer#105.