[R-pkg-devel] set pkg_config for 3rd party software

[Martin Maechler]

>>>>> Sameh M Abdulah 
>>>>>     on Fri, 30 Aug 2019 18:50:55 +0000 writes:

    > Hi,
    > I recently asked some questions about my R package which were well responded by Dirk.

    > I have another question related to pkg_config path,

    > I am using this command to add the installation path to the PKG_CONFIG_PATH   so that all cmake commands can get the required libraries from this path,

    > Sys.setenv(PKG_CONFIG_PATH=paste(Sys.getenv("PKG_CONFIG_PATH"),paste(.libPaths(),"exageostat/lib/pkgconfig",sep='/',collapse=':'),sep=':'))

    > Is there a simple way to set this path without explicitly calling this line before installing my package? OR is there any other path that I can use so that all software CMake commands can easily find the required libraries?

    > --Sameh

Not an answer, but a  #METOO   with a hopefull very related
question, also on using 'pkg-config' (Note: "-", not "_" here)
for package configuration.

I'm maintainer of CRAN package Rmpfr (for arbitrary precise arithmetic..),
    https://cran.r-project.org/package=Rmpfr
development & source on R-forge
     http://rmpfr.r-forge.r-project.org/
and  https://r-forge.r-project.org/scm/viewvc.php/pkg/?root=rmpfr
which "down there"  is principally an interface to the GNU MPFR
C library (which also needs the GNU  GMP C library).

I do have a  Rmpfr/configure.ac from which to produce
Rmpfr/configure which then ensures that both libraries (MPFR and GMP)
are found and are "working".
The 'configure' script then (supposedly, but not on Windows?) takes
either src/Makevars.in  (non-Windows)
or     src/Makevars.win (Windows)
to produce  src/Makevars
which then is used during compilation of the C sources of my
package.

Notably it will contain   '-lmpfr -lgmp'  among the LDFLAGS in
any case.

Now back to the 'pkg-config' : The compiler *also* needs correct

-I<path>  (the path used  by ' #include <...> ' statement)

and for linking a correct  -L<path>.

Now, my main OS,  Linux Fedora (as all other decent Linux distributions)
does provide MPFR and GMP libraries (and include headers) as OS
packages, installed in  /usr/lib/ (actually /lib64 nowadays)
and /usr/include respectively.

However, for some reasons I don't know the *version* of the MPFR
library that the OS provides is outdate (to my taste), and I'd
really want a newer version of MPFR,  which I easily install in
a version of /usr/local/..... *and* I also make sure that

    pkg-config --libs mpfr
and pkg-config --cflags mpfr

list the corresponding LDFLAGS  and CFLAGS

(the first giving

  -L/usr/local.../mpfr/4.0.1/lib -lmpfr -lgmp 

 the 2nd

  -I/usr/local.../mpfr/4.0.1/include 
)

Now what is the officially / best way to have either 'configure'
or  Makevars.{in,win}  use the 'pkg-config' information
*dynamically*, i.e.,
if I update my MPFR from 4.0.1 to 4.0.2  the newer 4.0.2 is found ?

My current setup would not even work on some platforms to really
end up using my local version of MPFR instead of the system-wide
OS default (using /lib64 and /usr/include/ and then
which even with quite new Fedora 30 is still MPFR 3.1.6 .. much
too old for some of the things I want).