[R-sig-Debian] problem with `viridis` on Ubuntu 20.04

[Samuele Carcagno]

I've hit a bug on Ubuntu 20.04. The issue occurred both with the R 
version that shipped with Ubuntu last week, and it is occurring now with 
the CRAN packages from one of the mirros (deb 
http://cran.mirror.garr.it/mirrors/CRAN/bin/linux/ubuntu/ 
focal-cran40/). The issue occurs whether I use the deb package for 
viridis in the Ubuntu repos, or I install it with `install.packages()` in R.

The issue is that when I call a function from the 'viridis' package 
(e.g. running the first example in the `viridis` vignette: 
https://cran.r-project.org/web/packages/viridis/vignettes/intro-to-viridis.html) 
R gets stuck indefinitely; the system monitor shows the R process using 
CPU resources but nothing happens at the terminal and I'm also unable to 
stop the function with Ctrl-C.

I did a little digging and simply calling the function `viridis` from 
the `viridisLite` package causes the same problem, execution gets stuck 
at the line:

     cols <- fn_cols(seq(begin, end, length.out = n)) / 255

which is line 177 here: 
https://github.com/sjmgarnier/viridisLite/blob/master/R/viridis.R#L177

I'm dual booting Debian Buster on the same machine and no such issue 
occurs with R 4.0.0 and the same versions of the `viridis` and 
`viridisLite` packages. Also no such issue occurs on Windows 10 or on a 
Mac both with R 4.0.0 and the latest versions of `viridis` and 
`viridisLite`.

I was not sure where should I report the bug, so I thought of asking for 
advice here first.

Best,

Sam