Go back to requiring only Perl 5.6+ for users

Commit 61901a1 dated 2022-07-10
bumped the Perl requirement to 5.10 or later, because
commit 3a9802d dated 2021-08-31
added code using Time::HiRes’s ‘stat’ function, a feature
added in Perl 5.8.9+ or Perl 5.10+, and it was hard
to find Perl 5.8.9 hosts to test with.  Also, requiring Perl 5.10
meant that we could then use operators like Digest::SHA, the // and
//= operators, the regexp \K escape, and ‘state’ variables.

However, that Time::HiRes code, which was taken from Automake, has
recently been made optional by Automake, and it now works again with
Perl 5.6.  And Autoconf is not yet using any other post-5.6 feature,
except when developers run help-extract.pl (something Autoconf users
do not use).  So relax the Autoconf user requirement back to 5.6 as it
was in Autoconf 2.71; although Autoconf developers will need 5.10 or
better, Autoconf users can get by with 5.6.

I ran into this problem when testing the Autoconf release candidate on
Solaris 10, which has Perl 5.8.4.  Oracle says Solaris 10’s
end-of-life is January 2024, so it’s still (barely) a viable porting
target.  Of course with Solaris 10 one must install a recent-enough
GNU m4, but adding a requirement to also install a recent-enough Perl
is a new barrier, and if it’s not needed then it might be better to
wait until it is needed (or until 2024 arrives).

* NEWS: Update news item about Perl 5.6 vs 5.10.
* README-hacking: Bump Perl recommendation to 5.10.
* build-aux/fetch.pl: Do not munge imported code to require 5.10.

NEWS

@@ -10,8 +10,15 @@ GNU Autoconf NEWS - User visible changes.
   means Autoconf no longer supports pre-1989 C compilers, as they do
   not support function prototypes.
 
-*** Autoconf now requires perl 5.10 (2007) or later.
-  Generated 'configure' scripts continue to run without perl.
+*** Autoconf developers now need Perl 5.10 (2007) or later.
+  Generated 'configure' scripts continue to run without Perl.
+
+  Although Autoconf users still need only Perl 5.6 (2000) or later,
+  Perl 5.10 or later is recommended for users too, as it avoids some
+  trouble with files that have timestamps separated by less than 1 s.
+  Due to limitations in Perl's API this trouble is not entirely fixed
+  even with Perl 5.36, which cannot represent timestamps separated by
+  238 ns or less, for circa 2023 timestamps on typical platforms.
 
 *** Autoconf now requires GNU M4 1.4.8 (2006) or later.
   Generated 'configure' scripts continue to run without M4.

README-hacking

@@ -17,7 +17,7 @@ tools we depend upon, including:
 - Automake 1.11+ <https://www.gnu.org/software/automake/>
 - Help2man 1.29+ <https://www.gnu.org/software/help2man/>
 - M4 1.4.16+ <https://www.gnu.org/software/m4/>
-- Perl 5.006+ <https://www.cpan.org/>
+- Perl 5.010+ <https://www.cpan.org/>
 - Texinfo 4.11+ <https://www.gnu.org/software/texinfo/>
 
 The following are useful as well, if you want to be able to run commands

build-aux/fetch.pl

@@ -240,7 +240,6 @@ ($$$$$$)
   # 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);
 }

configure.ac

@@ -153,7 +153,14 @@ AM_MISSING_PROG([HELP2MAN], [help2man])
 ## ------ ##
 
 # We use an absolute name for perl so the #! line in autoscan will work.
-AC_PATH_PERL_WITH_TIME_HIRES_STAT
+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])
+}
 
 # 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 5.010;
+use 5.006;
 use strict;
 use warnings FATAL => 'all';
 

lib/Autom4te/ChannelDefs.pm

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

lib/Autom4te/Configure_ac.pm

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

lib/Autom4te/General.pm

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

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 5.010;
+use 5.006;
 use strict;
 use warnings FATAL => 'all';