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Re: [sr #110215] AC_EGREP_HEADER appears to be broken in master

From: Eric Blake
Subject: Re: [sr #110215] AC_EGREP_HEADER appears to be broken in master
Date: Tue, 24 Mar 2020 15:17:31 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0

On 3/24/20 3:07 PM, Nick Bowler wrote:
On 2020-03-24, Ross Burton <address@hidden> wrote:
As to why this is not broken with 2.69, I think I have a theory.

If I build e.g. acl with both 2.69 and master, it's notable that 2.69
has these lines in the output that do not exist in master:

checking how to run the C preprocessor... gcc  -E
checking for grep that handles long lines and -e...
checking for egrep... /scratch/poky/hosttools/grep -E
checking for ANSI C header files... yes

Probably that is it: the long-obsolete AC_HEADER_STDC, previously
used internally by AC_INCLUDES_DEFAULT, used AC_EGREP_HEADER.  The
AC_HEADER_STDC macro is now a no-op (and is not used at all within
Autoconf anymore), so that change is likely what made the first use
of AC_EGREP_HEADER the one inside the if condition, causing the
observed results.

We already have autoupdate remove a call to AC_HEADER_STDC and replace it with the direct side-effect results of setting STDC_HEADERS and TIME_WITH_SYS_TIME; should we also tweak that to preserve the side-effect of AC_REQUIRES([AC_EGREP_HEADER)], to minimize the pain on external projects unaware that they were depending on that side-effect? Or maybe just tweak the NEWS blurb to mention that users depending on $GREP being set early may need to be careful?

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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