mkarchiso: read SOURCE_DATE_EPOCH from file early

When restarting an interrupted build, SOURCE_DATE_EPOCH needs to be
available before `profiledef.sh` is read, since it may reference it.

Fixes 7c6f266ec9

CHANGELOG.rst

@@ -23,10 +23,13 @@ Deprecated
 Fixed
 -----
 
+<<<<<<< HEAD
 - Wait for ``network-online.target`` to become active before trying to download the script passed via the ``script=``
   boot parameter.
 - Subdirectories from ``grub/`` are copied to the ISO.
 - Modify the commandline options to a ``cp`` command in ``mkarchiso`` so that the entire script does not exit with failure when a custom ``.bashrc`` file is supplied with the archiso configuration. This fix was needed after **GNU Coreutils** recently changed the behaviour of the ``-n`` (or ``--no-clobber``) commandline option to the ``cp`` command.
+- Ensure ``SOURCE_DATE_EPOCH`` is read from the ``build_date`` file before ``profiledef.sh`` is sourced to ensure the
+  variable has a correct value when used inside ``profiledef.sh``.
 
 Removed
 -------

archiso/mkarchiso

@@ -1742,12 +1742,8 @@ _build_iso_base() {
 
     # Create working directory
     [[ -d "${work_dir}" ]] || install -d -- "${work_dir}"
-    # Write build date to file or if the file exists, read it from there
-    if [[ -e "${work_dir}/build_date" ]]; then
-        SOURCE_DATE_EPOCH="$(<"${work_dir}/build_date")"
-    else
-        printf '%s\n' "$SOURCE_DATE_EPOCH" > "${work_dir}/build_date"
-    fi
+    # Write build date to file if it does not exist already
+    [[ -e "${work_dir}/build_date" ]] || printf '%s\n' "$SOURCE_DATE_EPOCH" > "${work_dir}/build_date"
 
     [[ "${quiet}" == "y" ]] || _show_config
     _run_once _make_pacman_conf
@@ -1863,6 +1859,13 @@ fi
 # get the absolute path representation of the first non-option argument
 profile="$(realpath -- "${1}")"
 
+# Read SOURCE_DATE_EPOCH from file early
+build_date_file="$(realpath -q -- "${override_work_dir:-./work}/build_date")" || :
+if [[ -f "$build_date_file" ]]; then
+    SOURCE_DATE_EPOCH="$(<"$build_date_file")"
+fi
+unset build_date_file
+
 _read_profile
 _set_overrides
 _validate_options