bug#64756: some frequent test failures

[Karl Berry]

Just to close this out: Bogdan worked up a patch to avoid the
fractional-second timestamps unless the new (current autoconf
development) autom4te is in used. Here is the basic change:
https://git.savannah.gnu.org/cgit/automake.git/commit/?id=b6fa73115d094c8d0da1d6759b6e7c7fca1f8a07
(also appended for the archive)

(Comments tweaked a little in subsequent changes.)

Jim is going to start working towards a release over the next days. 
--thanks, karl.


>From b6fa73115d094c8d0da1d6759b6e7c7fca1f8a07 Mon Sep 17 00:00:00 2001
From: Bogdan <bogdro_rep@gmx.us>
Date: Wed, 1 Nov 2023 17:40:47 -0700
Subject: m4: fall back to non-fractional timestamps with older autom4te.

* m4/sanity.m4 (_AM_FILESYSTEM_TIMESTAMP_RESOLUTION): if
HiRes is not present in Autom4te/FileUtils.pm, do not consider
fractional sleeps.
---
 m4/sanity.m4 | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/m4/sanity.m4 b/m4/sanity.m4
index db9a1f5..445d1fb 100644
--- a/m4/sanity.m4
+++ b/m4/sanity.m4
@@ -16,10 +16,28 @@ AS_IF([sleep 0.001 2>/dev/null], 
[am_cv_sleep_fractional_seconds=true], [am_cv_s
 # _AM_FILESYSTEM_TIMESTAMP_RESOLUTION
 # -----------------------------------
 # Determine the filesystem timestamp resolution.  Modern systems are nanosecond
-# capable, but historical systems could be millisecond, second, or even 
2-second
-# resolution.
+# capable, but historical systems could have millisecond, second, or even
+# 2-second resolution.
 AC_DEFUN([_AM_FILESYSTEM_TIMESTAMP_RESOLUTION], [dnl
 AC_REQUIRE([_AM_SLEEP_FRACTIONAL_SECONDS])
+#
+# Check if Autom4te uses Time::HiRes. If not, we cannot use fractional sleep,
+# because this sanity test and automated tests will be unreliable due to
+# Autom4te's caching of results and comparing timestamps.
+# More info: long thread around
+#     https://lists.gnu.org/archive/html/automake/2023-04/msg00002.html
+# and https://debbugs.gnu.org/cgi/bugreport.cgi?bug=64756.  
+AC_PATH_PROG([AUTOM4TE], [autom4te])
+if test x"$autom4te_perllibdir" = x; then
+  autom4te_perllibdir=`sed -n \
+   '/autom4te_perllibdir/{s/^.*|| //;s/;$//;s/^.//;s/.$//;p;q}' <$AUTOM4TE`
+fi
+if grep HiRes "$autom4te_perllibdir"/Autom4te/FileUtils.pm >/dev/null; then
+  :
+else
+  am_cv_sleep_fractional_seconds=false
+fi
+
 AC_CACHE_CHECK([the filesystem timestamp resolution], 
am_cv_filesystem_timestamp_resolution, [dnl
 # Use names that lexically sort older-first when the timestamps are equal.
 rm -f conftest.file.a conftest.file.b
-- 
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