Weird interactions between AC_PROG_CC and AC_PROG_F77

[Stefano Lattarini]

Hello everybody.

I encountered the following strage behaviour in the latest stable 
autoconf (2.65, Debian package version 2.65-2), and it really seems
a bug to me:

 $ cat > configure.ac <<EOF
 AC_INIT
 AC_PROG_CC
 AC_PROG_F77
 EOF
 $ autoconf
 $ ./configure CC=gcc F77=gfortran; echo rc=$? # works as expected
 checking for gcc... gcc
 checking whether the C compiler works... yes
 checking for C compiler default output file name... a.out
 checking for suffix of executables...
 checking whether we are cross compiling... no
 checking for suffix of object files... o
 checking whether we are using the GNU C compiler... yes
 checking whether gcc accepts -g... yes
 checking for gcc option to accept ISO C89... none needed
 checking whether we are using the GNU Fortran 77 compiler... yes
 checking whether gfortran accepts -g... yes
 rc=0
 $ ./configure CC=false F77=gfortran; echo rc=$? # fails as expected
 checking for gcc... false
 checking whether the C compiler works... no
 configure: error: in `/home/stefano/tmp':
 configure: error: C compiler cannot create executables
 See `config.log' for more details.
 rc=77
 $ ./configure CC=gcc F77=false; echo rc=$? # doesn't fail!
 checking for gcc... gcc
 checking whether the C compiler works... yes
 checking for C compiler default output file name... a.out
 checking for suffix of executables...
 checking whether we are cross compiling... no
 checking for suffix of object files... o
 checking whether we are using the GNU C compiler... yes
 checking whether gcc accepts -g... yes
 checking for gcc option to accept ISO C89... none needed
 checking whether we are using the GNU Fortran 77 compiler... no
 checking whether false accepts -g... no
 rc=0

-*-*-

And a specular behaviour can be observed by swapping the AC_PROG_CC
and AC_PROG_F77 macros in configure.ac:

 $ cat > configure.ac <<EOF
 AC_INIT
 AC_PROG_F77
 AC_PROG_CC
 EOF
 $ autoconf
 $ ./configure CC=gcc F77=gfortran; echo rc=$? # works as expected
 checking whether the Fortran 77 compiler works... yes
 checking for Fortran 77 compiler default output file name... a.out
 checking for suffix of executables...
 checking whether we are cross compiling... no
 checking for suffix of object files... o
 checking whether we are using the GNU Fortran 77 compiler... yes
 checking whether gfortran accepts -g... yes
 checking for gcc... gcc
 checking whether we are using the GNU C compiler... yes
 checking whether gcc accepts -g... yes
 checking for gcc option to accept ISO C89... none needed
 rc=0
 $ ./configure CC=gcc F77=false; echo rc=$? # fails as expected
 checking whether the Fortran 77 compiler works... no
 configure: error: in `/home/stefano/tmp':
 configure: error: Fortran 77 compiler cannot create executables
 See `config.log' for more details.
 rc=77
 $ ./configure CC=false F77=gfortran; echo rc=$? # doesn't fail!
 checking whether the Fortran 77 compiler works... yes
 checking for Fortran 77 compiler default output file name... a.out
 checking for suffix of executables...
 checking whether we are cross compiling... no
 checking for suffix of object files... o
 checking whether we are using the GNU Fortran 77 compiler... yes
 checking whether gfortran accepts -g... yes
 checking for gcc... false
 checking whether we are using the GNU C compiler... no
 checking whether false accepts -g... no
 checking for false option to accept ISO C89... unsupported
 rc=0

-*-*-

Finally, I observed the same behaviour with the latest autoconf from 
Git master branch (2.65.35-a2889).

-*-*-*-

System details:
  Debian GNU/Linux squeeze/sid
  GNU m4: 1.4.13
  Perl: v5.10.1 (Debian package version 5.10.1-8)
  GCC: 4.3.4
  gfortran: 4.3.4

Let me know if you need the generated configure scripts and/or
the config.log files.

Regards,
     Stefano