Re: error: possibly undefined macro: AC_CHECK_HEADERS_ONCE

[Bruno Haible]

Stepan Kasal wrote:
> The macro gl_INCLUDED_REGEX contains this:
>
>     m4_syscmd([test -f '$1'])
>     ifelse(m4_sysval, 0,
>       [ ...
>           gl_PREREQ_REGEX
>       ])
> ...
>
> Why is the above trick necessary?  Why should the macro expansion
> depend on the presence of the file?

That appears to be obsolete. As far as I see, there are no users of this
macro which don't also bundle regex.c.

> Second: just above the quoted code:
>
>     test -n "$1" || AC_MSG_ERROR([missing argument])
>
> yes, the macro gl_INCLUDED_REGEX requires a parameter, but why it should
> be reported in runtime?  (Yes, the parameter might be a shell variable,
> but is this done often?)

You're right, that should be turned into an AC_FATAL call.

> Third, the name regex.m4 conflicts with a file in Automake.  This can
> cause problems with "aclocal --include".

No, it cannot: This file in automake is not installed by automake. It's
private to automake. Furthermore it bears the comment
 "FIXME: This macro seems quite obsolete now since rx doesn't seem to be
  maintained, while regex is."
So it's likely automake's regex.m4 which will go away.

> Fourth, I noticed a typo; could you please apply the attached patch?

Thanks, applied. Let's see how many people still use autoconf-2.54 :-)

Bruno