Unexported (until v1.0.0) rlang functions used

[billybarc]

The dev version of ggplot2 uses on_load()/run_on_load() from rlang, but these functions are not exported for rlang versions < 1.0.0. I think the ggplot2 DESCRIPTION dependency needs to be upgraded to rlang >= 1.0.0.

I noticed this after getting the following error when trying to install the dev version of ggplot2 while only having rlang version 0.4.10:

* installing *source* package 'ggplot2' ...
** using staged installation
** R
** data
*** moving datasets to lazyload DB
** inst
** byte-compile and prepare package for lazy loading
Error in on_load({ : could not find function "on_load"
Error: unable to load R code in package 'ggplot2'
Execution halted
ERROR: lazy loading failed for package 'ggplot2'
Warning in install.packages :
  installation of package 'ggplot2' had non-zero exit status

Not sure what the reprex would be here other than installing specific versions of these packages with devtools::install_version(); can provide if needed.

Crosspost from stackoverflow.

[hadley]

Do you want to do a PR to fix this?