errors in dynamic() can give "restarting interrupted promise evaluation" warnings

[kevinushey]

We should see if we can avoid these. Examples:

options(
  renv.config.connect.timeout = 5L,
  renv.config.connect.retry = 0L
)

renv:::available_packages(type = "source", repos = "https://crab.rstudio.com")

Which gives:

> renv:::available_packages(type = "source", repos = "https://crab.rstudio.com")
* Querying repositories for available source packages ... Done!
Warning in value[[3L]](cond) :
  restarting interrupted promise evaluation
* Querying repositories for available source packages ... Done!
Warning: error downloading 'https://crab.rstudio.com/src/contrib/PACKAGES.rds' [curl: (6) Could not resolve host: crab.rstudio.com]
Warning: error downloading 'https://crab.rstudio.com/src/contrib/PACKAGES.gz' [curl: (6) Could not resolve host: crab.rstudio.com]
Warning: error downloading 'https://crab.rstudio.com/src/contrib/PACKAGES' [curl: (6) Could not resolve host: crab.rstudio.com]
Error: could not retrieve available packages for url 'https://crab.rstudio.com/src/contrib'

[kevinushey]

The simplest fix would probably be to give a callback function to dynamic() rather than a value.

EDIT: No, this isn't sufficient. 😞

[kevinushey]

Should be resolved now -- the key bit is ensuring we don't try to force the promise twice; that can happen if (for example) the promise is forced while a tryCatch() error handler is active that discards the error, e.g.

> foo <- function(x) { try(x); x }
> foo(stop())
Error in try(x) : 
Error in foo(stop()) : 
  (converted from warning) restarting interrupted promise evaluation