R devel - Jul 2014 - how to list external dependencies (i.e., non-R packages)?

hi.  i'm working on a package which only works if one (or both) of two
libraries (Imlib2 and MagickWand) exist on the machine on which the
package is compiled and executed.  as currently written, the program
purposely generates an error at *compile* time if neither library is
available (thinking the earlier the user is notified, the less
frustrating).

is there a way of specifying this dependency in, say, the DESCRIPTION
file?  (seems unlikely, as this is what the whole autotools/configure.ac
framework is supposed to deal with.)

or, should i take out the compile time error (maybe replace my #error
with a #warning), and just generate at error at run time?  (this will
require me to figure out what that means for build tests/, but obviously
some sort of hack is doable.)

cheers, Greg

Several packages in Bioconductor (and possibly CRAN) uses
  SystemRequirements
in DESCRIPTION, but unless the user reads the DESCRIPTION file, this is for
naught.  Still useful to some people I think.

Best,
Kasper


On Sun, Jul 13, 2014 at 9:13 PM, Greg Minshall <minshall@acm.org> wrote:
> hi.  i'm working on a package which only works if one (or both) of two
> libraries (Imlib2 and MagickWand) exist on the machine on which the
> package is compiled and executed.  as currently written, the program
> purposely generates an error at *compile* time if neither library is
> available (thinking the earlier the user is notified, the less
> frustrating).
>
> is there a way of specifying this dependency in, say, the DESCRIPTION
> file?  (seems unlikely, as this is what the whole autotools/configure.ac
> framework is supposed to deal with.)
>
> or, should i take out the compile time error (maybe replace my #error
> with a #warning), and just generate at error at run time?  (this will
> require me to figure out what that means for build tests/, but obviously
> some sort of hack is doable.)
>
> cheers, Greg
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
	[[alternative HTML version deleted]]

On Sun, Jul 13, 2014 at 12:13 PM, Greg Minshall <minshall at acm.org>
wrote:
>
> is there a way of specifying this dependency in, say, the DESCRIPTION
> file?  (seems unlikely, as this is what the whole autotools/configure.ac
> framework is supposed to deal with.)
As was mentioned, the SystemRequirements field allows for this, but
the format is quite informal and hence package managers cannot
automatically resolve such dependencies. A few years ago [1] it was
suggested on this mailing lists to extend the DESCRIPTION spec with
fields that allow package authors to specify which particular deb or
rpm packages are required to build the R package. However this was
shot down with the argument that it is not the responsibility of the
package author to determine the required build/runtime dependencies on
the OS of the user.

Debian/Ubuntu users can take advantage of the "debianized" packages
from cran2deb [2,3,4] which, among other benefits, do have the
capability to formally declare external dependencies. Such r-cran-xx
and r-bioc-xx packages will automatically install build/runtime
dependencies when needed  (e.g. libmagickwand-dev). Due to the
limitations above, this system currently relies on 3rd party
volunteers (with limited resources) to maintain a database [5] of
"Depends" and "Build-Depends" for all R packages. Dirk
Eddelbuettel,
Michael Rutter and Don Armstrong are doing a great job to keep this
system going and provide binary builds of many cran/bioc packages for
the various deb distributions. Creating a debianized version of your
own R package is quite easy too, and solves the problem at least for
your debian/ubuntu users :-)

I still think it would be useful to introduce a standard field/format
somewhere in the R package metadata that gives package authors the
option to suggest deb/rpm/homebrew dependencies required to build/use
the R package. But for now the best we can do is provide manual
instructions in the SystemRequirements+readme.

Jeroen


[1] https://stat.ethz.ch/pipermail/r-devel/2011-February/059787.html
[2] http://dirk.eddelbuettel.com/papers/useR2009cran2deb.pdf
[3]
http://www.personal.psu.edu/mar36/blogs/the_ubuntu_r_blog/cran2deb4ubuntu.html
[4] http://debian-r.debian.net/
[5] http://debian-r.debian.net/debian-r/c2d/