Re: [PATCH] warnings: fix compilation with old autoconf

[Bruno Haible]

Hi Eric,

> > Is m4_defun sufficient for AC_REQUIRE to work? The comments state that it is
> > essential that these macros can be AC_REQUIREd. This is needed for
> > gl_WARN_ADD (warnings.m4 line 94).
> 
> Yes.  Implementation-wise, autoconf has:
> 
> m4_copy([m4_defun],       [AC_DEFUN])
> 
> that is, AC_DEFUN is defined as a copy of the body of m4_defun,
> expanding to the same text.  Both AC_REQUIRE and m4_require are equally
> happy to pull in a macro, regardless of whether it defined via AC_DEFUN
> or m4_defun, making them interchangeable for what output is produced.
> 
> Therefore, the difference between the two macros is based solely on the
> fact that tracing depends on which macro name is invoked.

Well, then the Autoconf documentation at
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Macro-Definitions.html
is wrong. It states that the major difference between AC_DEFUN and m4_defun
is "some code that is used to constrain the order in which macros are
    called, while avoiding redundant output (-> AC_REQUIRE)".

Care to update the documentation?

Bruno