Fortan question & devel/fortrancl/Portfile ?

[Peter Danecek]

Hi all,

I am just browsing some Portfiles to understand how to handle fortran  
builds correctly.

At this point I came about something I may not understand in devel/ 
fortrancl/Portfile (or is it just a copy-paste bug?)

Why the g95 variant would depend on port:gcc45 ?

--- snip ---
variant gcc45 conflicts g95 description {build with gfortran-mp-4.5} {
   depends_build-append    port:gcc45
   configure.compiler      macports-gcc-4.5
}

variant g95 conflicts gcc45 description {build with g95} {
   depends_build-append    port:gcc45
   configure.fc            g95
}
--- snap ---

Now my question:
For the C compiler there is some default behaviour, how to choose the  
right compiler without depending on the actual system setup. Only in  
case a certain compiler version does not build, there is a possibility  
to influence the choice (at least this is what I understood).

I did not find any clear indications on how to do "the right thing"  
for Fortran compilers, and maybe there I no a completely clear  
strategy (???) on how to make Fortran compilation independent of the  
actual system. There are all these variants around. But for example if  
I have installed several versions of gccXX with the respective  
gfortran, I may end up with quite a mix of gfortran dependencies.

Then I observe that all these variants are usually conflicting.  
However, I guess (in theory) there are actually two different  
situations:

(1) I have some software written in fortran, and here obviously one  
single compiler is be fine (for example python extensions).
(2) I want to compile the fortran bindings of a library, to be used  
with "my preferred fortran compiler". Here I might want to install  
bindings for different compilers (or versions).

I guess, however the second case is not supported for the moment.

So which are the knobs to look at, when creating ports of fortran  
programs (or programs with fortran bindings)?

Maybe I just missed the right place to look at?

Thanks!
~petr