Cache docs contradictions: `EPIDATR_CACHE_DIRECTORY` (docs) vs `EPIDATR_CACHE_DIR` (code); `set_cache(dir = ...)` example vs `cache_dir` signature; README's `USE_EPIDATR_CACHE

[docxology]

Summary

While setting up the persistent cache I hit a contradiction between ?set_cache and the implementation: the documentation tells users to set EPIDATR_CACHE_DIRECTORY in .Renviron, but the code reads EPIDATR_CACHE_DIR; the same man page's example calls set_cache(dir = "...") although the argument is cache_dir; and the README's (non-rendered) comment refers to a USE_EPIDATR_CACHE variable that matches nothing in the codebase. Users following the documented workflow silently cache to the wrong location, and copying the documented example errors out. I believe the fixes are one-word renames in three places.

Evidence (dev tip 87b10e1; the EPIDATR_CACHE_DIRECTORY prose and EPIDATR_CACHE_DIR code are the same on main)

1. Prose vs. code — R/cache.R:17-20 (docs):

   environmental variables `EPIDATR_USE_CACHE=TRUE` and
   `EPIDATR_CACHE_DIRECTORY="/your/directory/here"`in your `.Renviron`, ...
   

   vs. R/cache.R:114-118 (code):

   cache_dir <- Sys.getenv(
     "EPIDATR_CACHE_DIR",
     unset = rappdirs::user_cache_dir("R", version = "epidatr")
   )

   The parameter table itself correctly says the env var is EPIDATR_CACHE_DIR (R/cache.R:81-84), so the man page contradicts itself.
2. Example vs. signature — R/cache.R:29-30 (docs): "you would call set_cache(dir = "~/my/temporary/savedirectory")" vs. the actual signature R/cache.R:106-113 (set_cache(cache_dir, days, max_size, logfile, confirm, startup)).
3. README comment — README.Rmd:49: "if you have USE_EPIDATR_CACHE=TRUE in your .Renviron" — the code reads EPIDATR_USE_CACHE (R/epidatr-package.R:11-14).

Maintainer-runnable repro

Sys.setenv(EPIDATR_CACHE_DIRECTORY = "/tmp/mydir")
set_cache(confirm = FALSE)
cache_info()$dir
# -> the default rappdirs location; /tmp/mydir was silently ignored

set_cache(dir = tempdir())
# Error in set_cache(dir = tempdir()) : unused argument (dir = tempdir())

Expected vs. actual

• Expected: following ?set_cache's documented workflow configures the cache location; the example runs.
• Actual: the documented env var is ignored (silent), and the documented example call errors.

Suggested fix

1. Use EPIDATR_CACHE_DIR in the prose (or accept both spellings in the code).
2. Change the example to set_cache(cache_dir = "~/my/temporary/savedirectory").
3. Correct the README comment to EPIDATR_USE_CACHE.

I checked for prior reports (open issues #193 "Opt-out-able cache notifications" and #198 "Add table of environmental cache variables" are adjacent; neither covers the wrong names) and found no existing report.