Debian (and other distributions) are trying to enforce "reproducible" builds, which means bit-identical. This requires using alternative build timestamps upon request, which all the compilers are set up to do. GNU APL is set up for it too, but there was a little bug that made it not work. Here is a patch.
$ cat debian/patches/0009-date.patch From: Jochen Sprickerhof <[email protected]> Date: Thu, 16 Jul 2026 20:03:31 +0200 Subject: [PATCH] Fix apl_BUILD_DATE computation - Remove space after equal sign as it is not allowed in shell. - Call date with -d @<timestamp> to set the correct date. --- m4/build_date.m4 | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/m4/build_date.m4 b/m4/build_date.m4 index bfaaccd..4299a6b 100644 --- a/m4/build_date.m4 +++ b/m4/build_date.m4 @@ -22,9 +22,9 @@ apl_BUILD_OS=$(uname -s -r -m) # current OS AS_IF( [test -n "$SOURCE_DATE_EPOCH"], [ apl_BUILD_OS="none" - apl_BUILD_DATE= $( - dash_format_date -u -d "$SOURCE_DATE_EPOCH" 2>/dev/null || - dash_format_date -u -r $SOURCE_DATE_EPOCH || + apl_BUILD_DATE=$( + dash_format_date -u -d "@$SOURCE_DATE_EPOCH" 2>/dev/null || + dash_format_date -u -d "@$SOURCE_DATE_EPOCH" || dash_format_date -u) ]) AC_SUBST([apl_BUILD_DATE])
