6.1 Forcing automake's choice of linking language

XXX no: there's an better mechanism, as yet undocumented. Watch this space, but don't use this technique.

When building a library or application, automake needs to make a decision about which language to use to do the final link. For example, it must use the Fortran linker to make a library which consists of or includes Fortran modules, and the C linker if it consists of pure C. This matters more on some platforms than others -- the OSX linker has some very fixed ideas on this point (it heartily disapproves of common blocks, and so needs special Fortran juju to make a library from Fortran which uses them).

Automake makes this decision based on the source code which is listed in the library's _SOURCES variable. When you are assembling a library purely from convenience libraries, however (see section `Linking static libraries' in the Libtool manual), the _SOURCES variable is empty, and automake ends up using the C linker, for want of any other information.

You can avoid this problem, and indicate to automake which langauge it should use, by giving a dummy value for the _SOURCES variable as follows:

libsubpar_adam_la_SOURCES = dummy_routine.f
libsubpar_adam_la_LIBADD = \
        subpar/libsubpar_convenience.la \
        parsecon/libparsecon_convenience.la

C A dummy Fortran routine.  See comments in Makefile.am
      SUBROUTINE DUMMY
      END

This is currently used in the `pcs', `gks', `astrom' and `pgplot' components.