Re: Avoiding g77

[John W. Eaton]

On 11/26/2014 11:41 AM, Daniel J Sebald wrote:
> On 11/26/2014 10:03 AM, Mike Miller wrote:
> > On Tue, Nov 25, 2014 at 23:08:41 -0800, Rik wrote:
> > > I think the best solution may be an explicit check for g77 and
> > > issuing an
> > > error message if it is selected.
> >
> > How about a version check instead? The g77 program only exists for gcc
> > <  4. Add a check for GFORTRAN_VERSION, and if it is a GNU compiler and
> > the version is less than 4, issue an error? That seems more robust
> > than checking for the name being g77.
> >
> > > I was concerned about the brittleness of the sed solution, and
> > > accidentally
> > > found that it is not robust.  The prologue which replaces g77 with
> > > gfortran
> > > is run at the end of the bootstrap sequence.  However, if the time
> > > stamp on
> > > configure.ac is modified, then the existing Makefiles take care of
> > > re-running aclocal, automake, and autoconf.  They do not run any
> > > bootstrap
> > > epilogue so the effect is to re-instate the default AC_PROG_F77 macro
> > > from
> > > autoconf which has g77 listed first.  If you are a developer,
> > > adjusting the
> > > time stamp can happen whenever you do an 'hg update' where there has
> > > been a
> > > change in configure.ac.  This is important because 'make dist'
> > > packages up
> > > the configure script that it finds into the tarball.  If one isn't
> > > aware of
> > > this oddity then the wrong configure script can be exported to
> > > everyone.  I
> > > checked the tarballs for versions 3.8.2, 3.8.1, 3.8.0, and 3.6.4 and
> > > they,
> > > at least, are clean.
> >
> > Agreed, that could happen. So are you proposing to delete
> > bootstrap_epilogue, and we say that an error check at configure-time
> > for g77 (or less than version 4) is enough to avoid the original
> > problem this was meant to solve? That sounds like a decent compromise
> > to me, especially now that systems with g77 are increasingly rare.
>
> I'm fine with the change as well.  The use of the epilogue isn't such a
> problem, as much as the sed modifying and overwriting the file "configure".
>
> One small variation on Rik's solution is the following:  If gfortran is
> our preferred compiler, we could first check for gfortran above all
> others using legal AC syntax, i.e.,
>
> AC_PROG_F77([gfortran])
> if F77 is not defined
>    AC_PROG_F77
>    if F77 is g77
>      error message "g77 is not supported, please choose another FORTRAN
> 77 compiler via environment variable F77
>    fi
> fi

This seems like a reasonable solution to me.  I'm not as concerned about 
g77 being installed with some other name, but if there is a way to 
identify g77 without just looking at the name of the program that would 
be fine with me too.

I agree that the problem I was trying to solve is probably not much of a 
problem now, though it certainly was for a while, when people had old 
versions of g77 installed that were incompatible with their version of GCC.

Thanks,

jwe