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Re: New failures with autoconf master

From: Nick Bowler
Subject: Re: New failures with autoconf master
Date: Wed, 18 Mar 2020 11:37:38 -0400

On 2020-03-18, Ross Burton <address@hidden> wrote:
> The flex issue is worked around by picking this commit from flex git:
> That refers to a mail sent to bug-autoconf in February 2018, with no reply:
[this mail describes observed problems when passing a literal 'dnl' to the
first argument of AC_CHECK_FUNCS]
> Any thoughts?

I think the linked mail stems from a misunderstanding of how m4 and
"dnl" work.

"dnl" is not really a comment like you may find in other programming
languages.  It is a macro, but one with very special semantics in that it
influences how m4 parses the remaining input whenever it is expanded.

The first argument to AC_CHECK_FUNCS is not subject to further expansion
within the expansion of AC_CHECK_FUNCS (very typical for macros which
take "string" arguments" in M4), so by quoting the dnl this means it is
never expanded and thus has no effect on the M4 processing.  So you have
a string containing these characters.

Just unquote the dnl and it will be expanded during argument collection
and it will have its usual effect.


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