Safer hook management

[vincentarelbundock]

@grantmcdermott and @etiennebacher,

Here’s a first attempt to resolve the tinytheme in a loop issue. The idea is:

1. Whenever tpar() sets a hook, we save that hook to the .tinyplot environment.
2. When tinytheme() resets the theme via init_tpar(), we retrieve the hooks from the .tinyplot environment and remove only the "before.plot.new" hooks that are identical() to those.

Implementation notes:

1. I copied the set_hooks() and remove_hooks() functions from the evaluate package and made a few minor changes to them. That package is MIT and included a note at the top of the file.
2. To make it easier to retrieve variables from the .tinyplot environment, I added a get_environment_variable() and set_environment_variable() functions.

The tests pass on my computer, and this seems to work.

I’m not exactly sure I know all the behaviors that were broken, so I’d appreciate if you could take this for a spin.

res <- evaluate::evaluate(function(){ 
    library(tinyplot)
    for (thm in c("dark", "minimal")) {
        tinytheme(thm)
        tinyplot(I(Sepal.Length * 1e4) ~ Petal.Length | Species, data = iris)
    }
})
sapply(res, class)
#> [1] "source"       "source"       "recordedplot" "recordedplot" "recordedplot"
#> [6] "recordedplot"

[vincentarelbundock]

CI error says this:

  Error: `cairo` must be a logical flag.
  Execution halted

but I have no idea what I did in the PR to generate it. Thoughts?

[vincentarelbundock]

Oh, I found the issue. Tests now pass.

[grantmcdermott]

Super thanks mate. I've been slammed, but hopefully able to review later today.

[grantmcdermott]

One thing in advance, please add a news item if you can. Takk.

[grantmcdermott]

Confirmed fix for yihui/knitr#2392

This is great, thanks @vincentarelbundock!