ccall mechanism in Julia

[Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>]

Hi Guix,

I'm currently packaging up Julia, a programming language for technical
computing.  When I configure the build process such that system
libraries are used instead of the bundled copies I run into a problem.

Julia's bindings to these libraries use the ccall mechanism; ccall
builds a map from library names to paths by parsing the output of
"ldconfig -p" at runtime.  I worked around this problem by patching the
sources to include a static map of library names to store paths.  Then I
noticed, however, that my patch effectively cripples the FFI.  It is no
longer possible to call a function that is exported by a shared library
unless it happens to be in the static map that is created at build time.

Before I hack a little more on the sources to implement a solution that
also considers libraries that happen to lie around in
~/.guix-profile/lib I would like to ask for comments.

Would it be a very bad idea if I wrote a simple replacement for
"ldconfig -p" that returned all libraries in the user's profile?  I
don't think this would be as bad as breaking the FFI and hard-coding
build-time paths to inputs.

What do you think?

~~ Ricardo