desc validate

[olivroy]

Hi, I wonder if it would be possible to implement the desc$validate() method.

I see that when you print a malformed description, it can show as red, but I don't understand the mechanism of how to use that generally.

I wonder if it would be possible to use the check_field() implementation, so that something like this could work out of the box.

desc$validate("Imports")
#> TRUE / FALSE or error?

It could therefore be used elsewhere like in pak or usethis to warn for malformed description.

I used usethis::use_tidy_description() with this as Imports

Imports:
  commonmark
  cli,
  dplyr

And no warning occured. The warning only occured as a pak cryptic error on gh actions, and I was not able to debug myself.

Cf : r-lib/pak#632

I would be happy to open a PR with some guidance.