Re: Makefile with .mod files from gfortran

[Brian Dessent]

Ignacio Fernández Galván wrote:

> a.mod a.o: a.f90 b.mod
>         gfortran -c $<
> 
> b.mod b.o: b.f90
>         gfortran -c $<

The reason that this misbehaves is that it violates rule number 2:
<http://make.paulandlesley.org/rules.html>.  Specifically, what you are
telling make with the above is: "to update a.mod, run gfortran -c
a.f90".  But that command does not necessarily update a.mod, so it's a
lie, and make gets confused.

Did you not see FX's reply on the fortran list? 
<http://gcc.gnu.org/ml/fortran/2007-11/msg00013.html>  His solution is
cleaner, since it effectively communicates to make that a.mod depends on
a.f90 and a.o, but without implying that the module can be rebuilt by
calling gfortran -c a.f90.  I think the @true part is even extraneous if
it looks too ugly.

Brian