mime package is used unconditionally, but is only in "Suggests"

[dmurdoch]

In this code:

https://github.com/yihui/xfun/blob/096985d288b747381aeeca1aa1cd8ff2b9ff6db8/R/base64.R#L80-L82

we see an unconditional call to mime::guess_type(x) from xfun::base64_uri(), an exported function. But mime is not in the Imports list, just in Suggests. There's a comment elsewhere (https://github.com/yihui/xfun/blob/f9ed8f7e0b3d544bd3c3a6cf9b204f515bcd8be4/R/markdown.R#L131) about a similar situation, but no comment here.

The problem is that my in-development package (at https://github.com/rgl2gltf) fails automatic checks, because it only gets to xfun in the chain of dependencies, and that doesn't force mime to be installed.

[yihui]

I forgot to mention it in the documentation, and will do it. Thanks for the report!

I don't want to add any hard dependencies to xfun. If other package authors want to use a function that requires other packages, they'd need to declare these packages as hard dependencies. However, if you don't use these packages directly, you will need a hack like https://github.com/atusy/minidown/commit/5761646d5a06f6fa406251542396c02b1eea5998 to avoid NOTEs in R CMD check.

[dmurdoch]

I think the docs would help, but a requireNamespace test in base64_uri (and the other functions using suggested packages) could give a more informative error message, e.g.

if (!requireNamespace("mime"))
  stop("The base64_uri() function requires the mime package.")`.

[yihui]

Done. Thanks for the report!

[yihui]

Just a quick followup: xfun has its own mime_type() function now, which does not have to depend on mime. It will use mime if available. If not, it will try some common MIME types defined in xfun:::mimemap. If still not found, it will try tools:::mime_type(). If that fails, it will resort to the command file --mime-type on *unix and PowerShell on Windows.