safe expression evaluation with callr

[schloerke]

Address scoping issues within #162

Pre rendered documents can now be rendered in a clean environment using:

learnr::safe(rmarkdown::render(FILE))

Tutorials should be able to be run in a clean environment using:

learnr::safe(learnr::run_tutorial(TUTORIAL))

This is done as rmarkdown has no intent on adding a new session for compilation. rstudio/rmarkdown#1204

[schloerke]

• NEWS item
• test

[wch]

It would be helpful to have a comment of why this function exists (because it's the same as the default for callr::r except that it allows opening a browser).

[schloerke]

Waiting to see response from r-lib/callr#72 about safe being adopted within callr

[schloerke]

callr does not want to include the safe function. Will keep within learnr

[wch]

I think having { } around code that's used as an expression is good for some contexts (e.g., shiny and profvis), but in this case, it might just be confusing for ordinary users of learnr.

For this example, I think you also don't want learnr::, to keep things simple for users.

Here's what you'd end up with after those two changes. This will be easier for new users to comprehend:

safe(run_tutorial("slidy", package = "learnr"))

[schloerke]

No problem, I can remove the brackets.

To get the code to work, I'd need to library the learnr package. Makes sense as it's in the learnr package.

[schloerke]

@wch Any idea on how to get around not having to require the user to say

safe(run_tutorial("slidly", package = "learnr", list(launch.browser = TRUE)))

as the run_tutorial is executed in a non interactive environment.

Environment variable?