justification for AC_LANG_ASSERT?

[Steven G. Johnson]

In a discussion about the AC_FC_FREEFORM macro (which figures out how to 
enable freeform-source support for Fortran, if possible), Akim wrote:

Akim Demaille wrote:
> I saw that you have wrapped many macros with AC_LANG_PUSH/POP.  I
> don't think this is the right thing to do.  Rather, you should require
> from the user to call these macros with the right current language.  I
> have appended some notes about this in the documentation.
> [...] 
> Index: ChangeLog
> from  Akim Demaille  <address@hidden>
>
>         * tests/fortran.at (GNU Fortran 77): Don't run FC macros.
>         (GNU Fortran): New.
>         * doc/autoconf.texi (Language Choice): Document.
>         * lib/autoconf/fortran.m4 (AC_FC_SRCEXT, AC_FC_FREEFORM): Assert
>         the current language is Fortran.

I just got an email from a user complaining about this, that

AC_PROG_FC(f90)
AC_FC_SRCEXT(f90)

no longer works in his configure.ac, and on reflection I'm questioning 
the decision to use AC_LANG_ASSERT, and indeed its raison d'etre.

What is the point of this macro?  Why would someone ever *not* want 
AC_FC_* to push Fortran itself?  Haven't they effectively declared that 
they want to use Fortran simply by calling the macro...why force them to 
call two additional macros to say that they really mean it?

Can we revert to the previous behavior?  (It won't break backwards 
compatibility, since people still *can* call AC_LANG_PUSH/POP.)

Moreover, why should any macro ever use AC_LANG_ASSERT rather than 
calling push/pop itself?  I don't understand the philosophy here.

Steven