mdate-sh: ignore $SOURCE_DATE_EPOCH (again).

* lib/mdate-sh: pay no attention to SOURCE_DATE_EPOCH.
The previous change (2025-05-15) was a misunderstanding;
looking at SOURCE_DATE_EPOCH causes spurious makeinfo rebuilds:
https://lists.gnu.org/archive/html/automake/2025-06/msg00021.html
* t/mdate5.sh: remove check for this.
* t/txinfo-vtexi4.sh: likewise.
* doc/automake.texi (Texinfo): remove mention of this.
* NEWS: update.

NEWS

@@ -5,8 +5,10 @@ please see NEWS-future and start following the advice there now.
 
   - Improve debuggability of installcheck failures. (bug#78850)
 
-  - Keep Automake tests working when SOURCE_DATE_EPOCH is set.
-  (https://lists.gnu.org/archive/html/automake/2025-06/msg00016.html)
+  - Undo change to mdate-sh; once again, it does not look at
+    SOURCE_DATE_EPOCH. This change was a misunderstanding that causes
+    problems, not fixes, for reproducible builds.
+    (https://lists.gnu.org/archive/html/automake/2025-06/msg00021.html)
 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 New in 1.18 (2025-05-25):

doc/automake.texi

@@ -8339,7 +8339,6 @@ Texinfo flags you can reference using @code{@@value@{EDITION@}},
 @code{@@value@{VERSION@}}, @code{@@value@{UPDATED@}}, and
 @code{@@value@{UPDATED-MONTH@}}.
 
-@vindex SOURCE_DATE_EPOCH@r{, and @command{mdate-sh}}
 @table @code
 @item EDITION
 @itemx VERSION
@@ -8347,12 +8346,11 @@ Both of these flags hold the version number of your program.  They are
 kept separate for historical reasons.
 
 @item UPDATED
-This holds the date the primary @file{.texi} file was last modified,
-or the date of the @env{SOURCE_DATE_EPOCH} variable (see below).
+This holds the date the primary @file{.texi} file was last modified.
 
 @item UPDATED-MONTH
 This holds the name of the month in which the primary @file{.texi} file
-was last modified, or the month of @env{SOURCE_DATE_EPOCH}.
+was last modified.
 @end table
 
 The @file{version.texi} support requires the @command{mdate-sh}
@@ -8360,17 +8358,6 @@ script; this script is supplied with Automake and automatically
 included when @command{automake} is invoked with the
 @option{--add-missing} option.
 
-@cindex reproducible builds
-@cindex epoch, and reproducible builds
-If the @env{SOURCE_DATE_EPOCH} environment variable is set,
-@command{mdate-sh} uses its value, instead of the modification time of
-any file.  This variable is typically set globally for the sake of
-creating a reproducible build across a distribution.  Its value is an
-integer, the number of seconds since the Unix epoch (January 1, 1970,
-00:00:00 UTC).  If for any reason the @env{SOURCE_DATE_EPOCH} value
-cannot be converted into the human-readable date strings,
-@command{mdate-sh} falls back to using the given file's mtime.
-
 If you have multiple Texinfo files, and you want to use the
 @file{version.texi} feature, then you have to have a separate version
 file for each Texinfo file.  Automake will treat any include in a

lib/mdate-sh

@@ -2,7 +2,7 @@
 # Get modification time of a file or directory, or value of
 # $SOURCE_DATE_EPOCH, and pretty-print it, formatted like 1 January 2000.
 
-scriptversion=2025-06-18.21; # UTC
+scriptversion=2025-06-25.21; # UTC
 
 # Copyright (C) 1995-2025 Free Software Foundation, Inc.
 # written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, June 1995
@@ -50,10 +50,6 @@ Usage: mdate-sh [--help] [--version] FILE
 Pretty-print the modification day of FILE, in the format:
 1 January 1970
 
-If the environment variable SOURCE_DATE_EPOCH is set, use its value (in
-epoch-seconds) for the date instead of any FILE mtime.  The FILE
-argument is still required in this case, but ignored.
-
 Report bugs to <bug-automake@gnu.org>.
 GNU Automake home page: <https://www.gnu.org/software/automake/>.
 General help using GNU software: <https://www.gnu.org/gethelp/>.
@@ -108,55 +104,6 @@ export LC_TIME
 TZ=UTC0
 export TZ
 
-# 
-# https://reproducible-builds.org/docs/source-date-epoch/
-if test -n "$SOURCE_DATE_EPOCH"; then
-  epoch_ok=true # be optimistic
-  date_fmt="+%d %B %Y"
-  result=`date -u --date="@$SOURCE_DATE_EPOCH" "$date_fmt" 2>/dev/null`
-  if test -z "$result"; then
-    result=`date -u -r "$SOURCE_DATE_EPOCH" "$date_fmt" 2>/dev/null`
-    if test -z "$result"; then
-      # The date command on Solaris 10 and 11 doesn't support any way
-      # to do this. Fall back to Perl.
-      #
-      perlout=`perl -e 'print scalar gmtime($SOURCE_DATE_EPOCH)' 2>/dev/null`
-      # Output is, e.g., Thu Jan  1 00:00:00 1970. Split it apart,
-      # since we need to convert "Jan" to "January".
-      # (We could use cut, but surely if a system has perl, it has awk?)
-      day=`echo $perlout | awk '{print $3}'`
-      mon=`echo $perlout | awk '{print $2}'`
-      mon_to_month $mon # sets $month
-      year=`echo $perlout | awk '{print $5}'`
-      result="$day $month $year"
-      #
-      if test -z "$result"; then
-        echo "$0: warning: SOURCE_DATE_EPOCH was set, but can't convert, ignoring: $SOURCE_DATE_EPOCH" >&2
-        epoch_ok=false
-      fi
-    fi
-  fi
-  #
-  if $epoch_ok; then
-    # Remove leading spaces and zeros. We don't want to get into the
-    # various date options to control this. (Not quoting $result here
-    # isn't important, just another way to omit leading spaces.)
-    result=`echo $result | sed 's/^[ 0]*//'`
-    if test -z "$result"; then
-      echo "$0: SOURCE_DATE_EPOCH was set, but converted to empty: $SOURCE_DATE_EPOCH" >&2
-      epoch_ok=false
-    fi
-  fi
-  if $epoch_ok; then
-    echo $result
-    exit 0
-  else
-    echo "$0: SOURCE_DATE_EPOCH failed, falling back to using mtime on: $1" >&2
-  fi
-fi
-# end of SOURCE_DATE_EPOCH support, rest is about the normal case of
-# using the mtime of the specified file.
-
 # 
 # GNU ls changes its time format in response to the TIME_STYLE
 # variable.  Since we cannot assume 'unset' works, revert this

t/mdate5.sh

@@ -30,7 +30,7 @@ test $# = 3
 case $1$3 in *[!0-9]*) exit 1;; esac
 test $1 -lt 32
 case $3 in
-  19[0-9][0-9]) :;; # for old SOURCE_DATE_EPOCH.
+  19[0-9][0-9]) :;; # just in case.
   20[0-9][0-9]) :;; # Hopefully automake will be obsolete in 80 years ;-)
   *) exit 1;;
 esac
@@ -40,26 +40,9 @@ case $2 in
   *) exit 1
 esac
 
-# Stricter checks on the year required a POSIX date(1) command,
-# and that SOURCE_DATE_EPOCH is not set.
-if year=$(date +%Y) \
-   && test -z "$SOURCE_DATE_EPOCH" \
-   && test $year -gt 2010; then
+# Stricter checks on the year require a POSIX date(1) command.
+if year=$(date +%Y) && test $year -gt 2010; then
   test $year = $3 || exit 1
 fi
 
-# 
-# Also check that mdate-sh respects SOURCE_DATE_EPOCH.
-SOURCE_DATE_EPOCH=123456 # into January 2, 1970, for no particular reason.
-export SOURCE_DATE_EPOCH
-set x $(./mdate-sh mdate-sh)
-shift
-echo "$*" # For debugging.
-
-# Check that mdate output is the expected day (1 January 1970):
-test $# = 3
-test x$1 = x2
-test x$2 = xJanuary
-test x$3 = x1970
-
 :

t/txinfo-vtexi4.sh

@@ -28,21 +28,11 @@ required='makeinfo tex texi2dvi grep-nonprint'
 # differ depending on local time.
 TZ=UTC0; export TZ
 
-if test -n "$SOURCE_DATE_EPOCH"; then
-  # use mdate-sh to parse SOURCE_DATE_EPOCH.
-  get_shell_script mdate-sh
-  result=`mdate-sh /irrelevant`
-  echo "result of mdate-sh: $result"
-  day=`echo $result | awk '{print $1}'`
-  month=`echo $result | awk '{print $2}'`
-  year=`echo $result | awk '{print $3}'`
-else
-  test $(LC_ALL=C date '+%u') -gt 0 && test $(LC_ALL=C date '+%u') -lt 8 \
-    && day=$(LC_ALL=C date '+%d')   && test -n "$day" \
-    && month=$(LC_ALL=C date '+%B') && test -n "$month" \
-    && year=$(LC_ALL=C date '+%Y')  && test -n "$year" \
-    || skip_ "'date' is not POSIX-compliant enough"
-fi
+test $(LC_ALL=C date '+%u') -gt 0 && test $(LC_ALL=C date '+%u') -lt 8 \
+  && day=$(LC_ALL=C date '+%d')   && test -n "$day" \
+  && month=$(LC_ALL=C date '+%B') && test -n "$month" \
+  && year=$(LC_ALL=C date '+%Y')  && test -n "$year" \
+  || skip_ "'date' is not POSIX-compliant enough"
 #
 day=$(echo "$day" | sed 's/^0//')