[R-pkg-devel] Help with detritus on temporary directory note

[Duncan Murdoch]

On 2024-05-30 7:43 a.m., Ivan Krylov via R-package-devel wrote:
> В Thu, 30 May 2024 11:12:05 +0200
> Héctor Meleiro Suárez <hmeleiros using gmail.com> пишет:
> 
>> So why is this a problem? Is it that there are too many files aftes
>> examples and tests are run? or would this NOTE be an issue to CRAN
>> even if only one file was detected at the end?
> 
> This problem has two sides.
> 
> The side that R CMD check is giving you NOTEs about is that _examples
> and tests_ are requried to keep the global state of the system intact.

Only some parts of the global state:  examples can create variables in 
globalenv().

Duncan Murdoch

> This includes all files on the computer: writing anywhere except the
> tempdir() is prohibited, and even that must be done with care not to
> overwrite anything and cleaned up afterwards.
> 
> (See https://cran.r-project.org/web/packages/policies.html and search
> for "temporary directory".)
> 
> The side that's more subjective is that outside tests and examples,
> code shouldn't be touching the filesystem without the user's
> permission. Many functions (e.g. write.table()) have a legitimate need
> to alter the filesystem. If the user would legitimately benefit from not
> having to download the files again (including between R sessions), feel
> free to follow the advice of Thierry Onkelinx and use
> tools::R_user_dir(...), except in tests and examples.
> 
> Testing functions that access external resources over the Internet is
> fraught with additional peril. Your examples and tests must not fail if
> a download attempt fails, but your users will probably prefer your
> functions to stop() with an exception on download failure. One way to
> solve this problem is to make sure that the functions that fetch
> anything from the Internet raise errors with a specific class set and
> then to wrap all examples and tests in tryCatch(...,
> yourpackage_Internet_error = function(e) message('Caught an error while
> accessing an Internet resource: ', conditionMessage(e))). This way any
> other unchecked errors (that your tests attempt to uncover) will still
> surface.
>