Require Perl 5.10.0 or later.

The minimum Perl version was raised to 5.8.0 from 5.6.0 in commit
3a9802d601 (but not documented as
such until e8c2d79ec4, and not
actually *enforced* by our own configure script until, er, now)
in order to use Time::HiRes::stat.

Unfortunately, while the Time::HiRes *module* was added in 5.8.0, it
did not export a ‘stat’ function until 5.8.9.  More precisely, this
feature was added to Time::HiRes in version 1.92 of that module; Perl
core 5.8.8 shipped Time::HiRes 1.86, 5.8.9 shipped 1.9715.  The only
system I have convenient access to, that has older Perls installed,
offers me a choice of 5.8.8 or 5.10.1, so the new requirement means
I cannot test with 5.8.x anymore.

Per https://perldoc.perl.org/perlhist the release history of these
versions of Perl is, in chronological order,

  5.8.0         2002-Jul-18
  5.8.8         2006-Jan-31
  5.10.0        2007-Dec-18
  5.8.9         2008-Dec-14  <-- almost a year later than 5.10.0
  5.10.1        2009-Aug-22
  5.12.0        2010-Apr-12

Per https://perldoc.perl.org/perl5101delta the differences between
5.10.0 and 5.10.1 are small, and do not make me worry about
accidentally introducing code that works on my test boxes but not for
our users, unlike the gulf between 5.8.x and 5.10.x.

Requiring 5.10 will mean that we have access to Digest::SHA, the //
and //= operators, the regexp \K escape, and ‘state’ variables
(lexical scope, persistent value) all of which I can think
of uses for (but none of them are actually used in this patch).

Putting it all together, I think a requirement bump to version 5.10.0
is justified.  We are already chopping off the trailing edge at 2006
due to the requirement for M4 1.4.8 (/de facto/ since 2.70) and late
2007 is still 15 years ago.

This patch also makes configure search $PATH for executables named
‘perl5*’ and ‘perl-5.*’ if bare ‘perl’ is too old.  To do this, it
introduces a helper macro AClocal_PATH_PROG_GLOBS_FEATURE_CHECK, which
I would *like* to promote to a new Autoconf feature, but I got stuck
on quoting issues — see comments in m4/perl-time-hires.m4.

* NEWS: Document requirement for Perl 5.10.
* m4/perl-time-hires.m4: New file.
* configure.ac: Use AC_PATH_PERL_WITH_TIME_HIRES_STAT to probe for
  perl.
* build-aux/fetch.pl (fetch): For .pm files fetched from Automake,
  rewrite “use 5.006” to “use 5.010”.

* build-aux/help-extract.pl
* lib/Autom4te/C4che.pm
* lib/Autom4te/ChannelDefs.pm
* lib/Autom4te/Channels.pm
* lib/Autom4te/Config.pm
* lib/Autom4te/Configure_ac.pm
* lib/Autom4te/FileUtils.pm
* lib/Autom4te/General.pm
* lib/Autom4te/Getopt.pm
* lib/Autom4te/Request.pm
* lib/Autom4te/XFile.pm
* tests/mktests.pl: Change “use 5.006” to “use 5.010”.

NEWS

@@ -4,7 +4,7 @@ GNU Autoconf NEWS - User visible changes.
 
 ** Backward incompatibilities
 
-*** Autoconf now requires perl 5.8 (2002) or later.
+*** Autoconf now requires perl 5.10 (2007) or later.
   Generated 'configure' scripts continue to run without perl.
 
 *** Autoconf now requires GNU M4 1.4.8 (2006) or later.

build-aux/fetch.pl

@@ -240,6 +240,7 @@ sub fetch ($$$$$$)
   # don't use \s here or it will eat blank lines
   $content =~ s/[ \t]+$//gm;
   $content =~ s/\bAutomake::/Autom4te::/g if $edit;
+  $content =~ s/^use 5\.006;$/use 5.010;/mg if $edit;
 
   replace_if_change ($destpath, $content, $quiet);
 }

build-aux/help-extract.pl

@@ -16,6 +16,7 @@
 
 # Written by Zack Weinberg.
 
+use 5.010;
 use strict;
 use warnings;
 

configure.ac

@@ -153,14 +153,7 @@ AM_MISSING_PROG([HELP2MAN], [help2man])
 ## ------ ##
 
 # We use an absolute name for perl so the #! line in autoscan will work.
-AC_PATH_PROG([PERL], [perl], [no])
-AC_SUBST([PERL])dnl
-if test "$PERL" = no; then
-  AC_MSG_ERROR([perl is not found])
-fi
-$PERL -e 'require 5.006;' || {
-   AC_MSG_ERROR([Perl 5.006 or better is required])
-}
+AC_PATH_PERL_WITH_TIME_HIRES_STAT
 
 # Find out whether the system supports flock
 # Note this test does not try to find out whether it works with this

lib/Autom4te/C4che.pm

@@ -31,7 +31,7 @@ This Perl module handles the cache of M4 runs used by autom4te.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/ChannelDefs.pm

@@ -44,7 +44,7 @@ shorthand function to output on specific channels.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/Channels.pm

@@ -66,7 +66,7 @@ etc.) that can also be overridden on a per-message basis.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/Config.pm

@@ -25,7 +25,7 @@ package Autom4te::Config;
 # and autoconf's build machinery is not prepared to do that.
 # Revisit after 2.70.
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/Configure_ac.pm

@@ -20,7 +20,7 @@
 
 package Autom4te::Configure_ac;
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/FileUtils.pm

@@ -34,7 +34,7 @@ This perl module provides various general purpose file handling functions.
 
 =cut
 
-use 5.008;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/General.pm

@@ -32,7 +32,7 @@ used in several executables of the Autoconf package.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/Getopt.pm

@@ -30,7 +30,7 @@ line options in conformance to the GNU Coding standards.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/Request.pm

@@ -32,7 +32,7 @@ used in several executables of the Autoconf and Automake packages.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/XFile.pm

@@ -69,7 +69,7 @@ and C<getlines> methods to translate C<\r\n> to C<\n>.
 
 =cut
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';
 

m4/perl-time-hires.m4

@@ -0,0 +1,74 @@
+# perl-time-hires.m4 serial 1
+
+# Copyright (C) 2022 Free Software Foundation, Inc.
+
+# Copying and distribution of this file, with or without modification,
+# are permitted in any medium without royalty provided the copyright
+# notice and this notice are preserved.  This file is offered as-is,
+# without warranty of any kind.
+
+# AClocal_PATH_PROG_GLOBS_FEATURE_CHECK
+# ---------------------------------
+# Like AC_PATH_PROGS_FEATURE_CHECK, but each of 'progs-to-check-for' may
+# be a shell glob, which is expanded once for each path entry.
+# That is, AClocal_PATH_PROG_GLOBS_FEATURE_CHECK([PERL], [perl-*]) will
+# test each program named something like 'perl-*' found anywhere on the
+# path.  Due to the syntax conflict with Autoconf string quoting,
+# character sets (e.g. perl-[56]*) are not supported.
+m4_define([AClocal_PATH_PROG_GLOBS_FEATURE_CHECK],
+[if test -z "$$1"; then
+  ac_path_$1_found=false
+  # Loop through the user's path and test for each of PROGNAME-LIST
+  dnl AS_ESCAPE has been excessively optimized and does not work for anything
+  dnl other than constructing strings.  I have not been able to figure out how
+  dnl to get [ and ] through this process without mangling them, so
+  dnl character sets are not supported for now.
+  _AS_PATH_WALK([$5],
+  [for ac_prog in m4_bpatsubst([$2], [[!?*]], [\\\&])
+   do
+    for ac_exec_ext in '' $ac_executable_extensions; do
+      ac_pathglob_$1="$as_dir$ac_prog$ac_exec_ext"
+      for ac_path_$1 in $ac_pathglob_$1; do
+        AS_EXECUTABLE_P(["$ac_path_$1"]) || continue
+$3
+        $ac_path_$1_found && break 4
+      done
+    done
+  done])dnl
+  if test -z "$ac_cv_path_$1"; then
+    m4_default([$4],
+      [AC_MSG_ERROR([no acceptable m4_bpatsubst([$2], [ .*]) could be dnl
+found in m4_default([$5], [\$PATH])])])
+  fi
+else
+  ac_cv_path_$1=$$1
+fi
+])
+
+# AC_PATH_PERL_WITH_TIME_HIRES_STAT
+# ---------------------------------
+# Check for a version of perl that supports Time::HiRes::stat.
+# This was added to perl core in 5.10 and it's convenient to
+# have a consistent 'use 5.0xx' baseline for all the perl scripts,
+# so that is the version we require, even though technically we
+# could be getting away with 5.8 or even 5.6 in many of the scripts.
+# (Note: Files shared with Automake do not necessarily use our baseline.)
+AC_DEFUN([AC_PATH_PERL_WITH_TIME_HIRES_STAT],
+  [AC_ARG_VAR([PERL], [Location of Perl 5.10 or later.  Defaults to
+    the first program named 'perl', 'perl5*', or 'perl-5.*' on the PATH
+    that meets Autoconf's needs.])
+  AC_CACHE_CHECK([for Perl >=5.10.0 with Time::HiRes::stat],
+                 [ac_cv_path_PERL],
+    [AClocal_PATH_PROG_GLOBS_FEATURE_CHECK(
+        [PERL], [perl perl5* perl-5.*],
+        [AS_ECHO("$as_me:${as_lineno-$LINENO}: trying $ac_path_PERL") \
+             >&AS_MESSAGE_LOG_FD
+         $ac_path_PERL >&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD -e '
+  use 5.010;
+  use Time::HiRes qw(stat);
+  1;' \
+         && ac_cv_path_PERL=$ac_path_PERL ac_path_PERL_found=:],
+    [AC_MSG_ERROR([no acceptable perl could be found in \$PATH.
+Perl 5.10.0 or later is required, with Time::HiRes::stat.])])])
+  PERL=$ac_cv_path_PERL
+])

tests/mktests.pl

@@ -17,7 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-use 5.006;
+use 5.010;
 use strict;
 use warnings FATAL => 'all';