Implements {fetch,configure,build,install}_clean.

build.sh:buildp_dispatch_fail_pkg(): print NL when writing to ${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}.
etc/{README.md,build.usage}: updated.
midipix.env: updated.
subr.rtl/rtl_complex.subr:rtl_sunset(): initial implementation.
subr.rtl/rtl_list.subr:rtl_l{filter[23],length2,lift[23]}(): initial implementation.
subr.rtl/rtl_state.subr:rtl_state_test(): take ${_build_steps} vs. ${_build_step}.
subr/{build_init,ex_pkg_restart}.subr: splits extended restart syntax processing logic.
subr/ex_pkg_exec.subr:ex_pkg_exec(): filter "start".
subr/pkg_{build,configure,fetch,install}_clean.subr: initial implementation.

7 files changed, 389 insertions, 156 deletions

diff --git a/subr/build_init.subr b/subr/build_init.subr
index f5894e69..2d78da91 100644
--- a/subr/build_init.subr
+++ b/subr/build_init.subr
@@ -2,145 +2,8 @@
 # set +o errexit -o noglob -o nounset is assumed.
 #
 
-buildp_expand_restart_at() {
-	local _restart_at_spec="${1}" _restart_at="" _restart_at_spec_new="";
-
-	for _restart_at in $(rtl_llift "${_restart_at_spec}" "," " "); do
-		case "${_restart_at}" in
-		@fetch)	_restart_at="fetch_download,fetch_extract"; ;;
-		@configure)
-			_restart_at="configure_patch_pre,configure_autotools,configure_patch,configure"; ;;
-		@build)	_restart_at="build"; ;;
-		@install)
-			_restart_at="install_subdirs,install_make,install_files,install_libs,install,install_rpm"; ;;
-		@clean)
-			_restart_at="clean"; ;;
-		*)	;;
-		esac;
-		_restart_at_spec_new="$(rtl_lconcat "${_restart_at_spec_new}" "${_restart_at}" ",")"
-	done;
-	printf "%s" "${_restart_at_spec_new}";
-};
-
-buildp_expand_restart_recursive() {
-	local _restart_spec="${1}" _last_pkg="" _restart_spec_at="" _restart_spec_recursive=0;
-
-	case "${_restart_spec}" in
-	\*\*\*[a-zA-Z]*)
-			_restart_spec="${_restart_spec#\*\*\*}"; _restart_spec_recursive=3; ;;
-	\*\*[a-zA-Z]*)	_restart_spec="${_restart_spec#\*\*}"; _restart_spec_recursive=2; ;;
-	\*[a-zA-Z]*)	_restart_spec="${_restart_spec#\*}"; _restart_spec_recursive=1; ;;
-	ALL)		_restart_spec_at=ALL; _restart_spec_recursive=2; ;;
-	LAST)		_restart_spec_at=ALL; _restart_spec_recursive=0;
-			if [ -n "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]\
-			&& [ -e "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]; then
-				_last_pkg="$(cat "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}")";
-				rtl_fileop rm "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}";
-				rtl_state_clear "${BUILD_WORKDIR}" "${_last_pkg}";
-				_restart_spec="${_last_pkg}";
-			else
-				_status="cannot rebuild last failed package"; return 1;
-			fi; ;;
-	esac;
-	ARG_RESTART="${_restart_spec}";
-	ARG_RESTART_AT="${_restart_spec_at}";
-	ARG_RESTART_RECURSIVE="${_restart_spec_recursive}";
-	return 0;
-};
-
-buildp_process_restart_spec() {
-	local _restart_spec="${1}" _eqfl=0 _ltfl=0 _restart_spec_at0="" _restart_spec_at="" _step="" _step1=""; _status="";
-
-	buildp_expand_restart_recursive "${_restart_spec}" || return "${?}";
-	_restart_spec="${ARG_RESTART}"; _restart_spec_at="${ARG_RESTART_AT}";
-
-	case "${_restart_spec}" in
-	"")	return 0; ;;
-	*:*)
-		_restart_spec_at="${_restart_spec#*:}"; _restart_spec="${_restart_spec%%:*}";
-		_restart_spec_at0="${_restart_spec_at}"; _restart_spec_at="";
-		case "${_restart_spec_at0}" in
-		ALL|LAST)
-			_restart_spec_at="${_restart_spec_at0}"; ;;
-
-		^*)	_restart_spec_at0="${_restart_spec_at0#^}";
-			_restart_spec_at0="$(buildp_expand_restart_at "${_restart_spec_at0}")";
-			_restart_spec_at="$(rtl_llift "${DEFAULT_BUILD_STEPS}" " 	" ",")";
-			for _restart_at in $(rtl_llift "${_restart_spec_at0}" "," " "); do
-				_restart_spec_at="$(rtl_lfilter "${_restart_spec_at}" "${_restart_at}" ",")";
-			done; _restart_spec_at="$(rtl_lfilter "${_restart_spec_at}" "finish" ",")"; ;;
-
-		\<=*|\<*|\>=*|\>*)
-			[ "${_restart_spec_at0#<}" != "${_restart_spec_at0}" ] && _ltfl=1;
-			if [ "${_restart_spec_at0#[<>]=}" != "${_restart_spec_at0}" ]; then
-				_restart_spec_at0="${_restart_spec_at0#[<>]=}"; _eqfl=1;
-			else
-				_restart_spec_at0="${_restart_spec_at0#[<>]}"; _eqfl=0;
-			fi; _restart_spec_at="";
-			_restart_spec_at0="$(buildp_expand_restart_at "${_restart_spec_at0%%,*}")";
-			if [ \( "${_eqfl}" -eq 1 \) -a \( "${_ltfl}" -eq 1 \) ]\
-			|| [ \( "${_eqfl}" -eq 0 \) -a \( "${_ltfl}" -eq 0 \) ]; then
-				_restart_spec_at0="${_restart_spec_at0##*,}";
-			elif [ \( "${_eqfl}" -eq 1 \) -a \( "${_ltfl}" -eq 0 \) ]\
-			||   [ \( "${_eqfl}" -eq 0 \) -a \( "${_ltfl}" -eq 1 \) ]; then
-				_restart_spec_at0="${_restart_spec_at0%%,*}";
-			fi;
-			for _restart_at in ${DEFAULT_BUILD_STEPS}; do
-				if [ "${_ltfl}" -eq 1 ]; then
-					if [ "${_restart_at}" = "${_restart_spec_at0%%,*}" ]; then
-						if [ "${_eqfl}" -eq 1 ]; then
-							_restart_spec_at="$(rtl_lconcat "${_restart_spec_at}" "${_restart_at}" ",")";
-						fi; break;
-					fi;
-				else
-					if [ "${_restart_at}" = "${_restart_spec_at0%%,*}" ]; then
-						_foundfl=1; [ "${_eqfl}" -eq 0 ] && continue;
-					fi; [ "${_foundfl}" -eq 0 ] && continue;
-				fi;
-				_restart_spec_at="$(rtl_lconcat "${_restart_spec_at}" "${_restart_at}" ",")";
-			done; ;;
-
-		*)	_restart_spec_at="$(buildp_expand_restart_at "${_restart_spec_at0}")"; ;;
-		esac; ;;
-
-	*)	_restart_spec_at=ALL; ;;
-	esac;
-
-	ARG_RESTART="$(rtl_llift "${_restart_spec}" "," " ")";
-	ARG_RESTART_AT="${_restart_spec_at}";
-	if [ "${#ARG_RESTART_AT}" -eq 0 ]; then
-		_status="zero-length build step list"; return 1;
-	elif [ "${ARG_RESTART_AT}" != "ALL" ]\
-	&&   [ "${ARG_RESTART_AT}" != "LAST" ]; then
-		for _restart_at in $(rtl_lfilter "$(rtl_llift "${ARG_RESTART_AT}" "," " ")" "${DEFAULT_BUILD_STEPS}"); do
-			case "${_restart_at}" in
-			start)	;;
-			*)	_status="unknown build step \`${_restart_at}'"; return 1; ;;
-			esac;
-		done;
-	fi;
-	if [ "${#ARG_RESTART_AT}" -gt 0 ]\
-	&& [ "${ARG_RESTART_AT}" != "ALL" ]\
-	&& [ "${ARG_RESTART_AT}" != "LAST" ]; then
-		_restart_spec_at="${ARG_RESTART_AT}"; ARG_RESTART_AT="";
-		for _restart_at in ${DEFAULT_BUILD_STEPS}; do
-			if rtl_lmatch "${_restart_spec_at}" "${_restart_at}" ","; then
-				ARG_RESTART_AT="$(rtl_lconcat "${ARG_RESTART_AT}" "${_restart_at}" ",")";
-			fi;
-		done;
-		if [ "${ARG_RESTART_AT##*,}" != "finish" ]; then
-			_step="$(rtl_lfilter "${ARG_RESTART_AT}" "clean,finish" ",")"; _step="${_step##*,}";
-			_step1="$(rtl_lfilter "${DEFAULT_BUILD_STEPS}" "clean finish")"; _step1="${_step1##* }";
-			if [ "${_step}" = "${_step1}" ]; then
-				ARG_RESTART_AT="$(rtl_lconcat "${ARG_RESTART_AT}" "finish" ",")";
-			fi;
-		fi;
-	fi;
-	return 0;
-};
-
 buildp_init_args() {
-	local	_eqfl=0 _foundfl=0 _group="" _pkg_names_unknown="" _rc=0	\
+	local	_foundfl=0 _group="" _pkg_names_unknown="" _rc=0	\
 		EX_PKG_BUILD_GROUPS EX_PKG_BUILD_GROUPS_NOAUTO; _status="";
 
 	case "${ARG_FETCH_FORCE}" in
@@ -149,26 +12,26 @@ buildp_init_args() {
 	ipv6)	DEFAULT_GIT_ARGS="$(rtl_lconcat "-6" "${DEFAULT_GIT_ARGS}")";
 		DEFAULT_WGET_ARGS="$(rtl_lconcat "-6" "${DEFAULT_WGET_ARGS}")"; ;;
 	esac;
-	if [ -z "${BUILD_HNAME:-}" ]\
+	if [ "${BUILD_HNAME:+1}" != 1 ]\
 	&& ! BUILD_HNAME="$(hostname)"; then
 		_rc=1; _status="Error: failed to obtain hostname.";
 	elif [ "${ARG_DUMP_ON_ABORT:-0}" -eq 1 ]\
-	&& [ "${ARG_RELAXED:-0}" -eq 1 ]; then
+	&&   [ "${ARG_RELAXED:-0}" -eq 1 ]; then
 		_rc=1; _status="Error: --dump-on-abort excludes -R.";
 	elif [ "${ARG_AS_NEEDED:-0}" -eq 1 ]\
-	&& [ -e "${PREFIX}/build.gitref" ]\
-	&& [ "$(git rev-parse HEAD)" = "$(cat "${PREFIX}/build.gitref")" ]; then
+	&&   [ -e "${PREFIX}/build.gitref" ]\
+	&&   [ "$(git rev-parse HEAD)" = "$(cat "${PREFIX}/build.gitref")" ]; then
 		_rc=0; _status="Git repository has not changed since last build and --as-needed was specified.";
-	elif ! buildp_process_restart_spec "${ARG_RESTART:-}"; then
+	elif ! ex_pkg_process_restart_spec \$ARG_RESTART \$ARG_RESTART_AT \$ARG_RESTART_RECURSIVE; then
 		_rc=1; _status="Error: failed to process -r specification: ${_status}.";
 	elif ! ex_pkg_load_groups; then
 		_rc=1; _status="Error: failed to load build groups.";
 	else	if ! rtl_lmatch "${ARG_DIST:-}" "rpm" ","\
-		&& [ -z "${ARG_DUMP_IN:-}" ]\
+		&& [ "${ARG_DUMP_IN:+1}" != 1 ]\
 		&& [ "${ARG_DUMP_ON_ABORT:-0}" -eq 0 ]; then
 			EX_PKG_BUILD_GROUPS="$(rtl_lfilter "${EX_PKG_BUILD_GROUPS}" "host_deps_rpm")";
 		fi;
-		if [ -z "${BUILD_GROUPS}" ]; then
+		if [ "${BUILD_GROUPS:+1}" != 1 ]; then
 			BUILD_GROUPS="${EX_PKG_BUILD_GROUPS}";
 		else	_foundfl=0; for _group in ${BUILD_GROUPS}; do
 				if rtl_lmatch "${EX_PKG_BUILD_GROUPS}" "${_group}"; then
@@ -184,10 +47,11 @@ buildp_init_args() {
 			fi;
 		fi;
 		if [ "${_rc:-0}" -eq 0 ]; then
-			if [ -n "${ARG_DIST}" ]; then
+			if [ "${ARG_DIST:+1}" = 1 ]; then
 				BUILD_GROUPS="$(rtl_lconcat "$(rtl_lfilter "${BUILD_GROUPS}" "dist")" "dist")";
 			fi;
-			if [ -n "${ARG_RESTART}" ] && ! rtl_lmatch "${ARG_RESTART}" "ALL LAST"; then
+			if [ "${ARG_RESTART:+1}" = 1 ]\
+			&& ! rtl_lmatch "${ARG_RESTART}" "ALL LAST"; then
 				for _pkg_name in ${ARG_RESTART}; do
 					if ! ex_pkg_find_package "${BUILD_GROUPS}" "${_pkg_name}" >/dev/null; then
 						_pkg_names_unknown="$(rtl_lconcat "${_pkg_names_unknown}" "${_pkg_name}")";
@@ -205,6 +69,7 @@ buildp_init_args() {
 
 buildp_init_env() {
 	local _fname="" _rc=0; _status="";
+
 	if ! cd "${0%/*}"; then
 		printf "Error: failed to change working directory to \`${0%/*}'." >&2; exit 1;
 	elif ! umask 022; then
@@ -221,6 +86,7 @@ buildp_init_env() {
 
 buildp_init_files() {
 	local _log_last_fname="" _log_last_num=1 _rc=0; _status=""
+
 	if ! rtl_fileop mkdir "${BUILD_DLCACHEDIR}" "${BUILD_WORKDIR}"\
 	|| rtl_lmatch "${ARG_DIST}" "rpm" ","\
 	&& ! rtl_fileop mkdir "${PREFIX_RPM}"; then
@@ -359,16 +225,11 @@ buildp_init_getopts() {
 };
 
 buildp_init_prereqs() {
-	if ! rtl_check_prereqs \
-			awk bunzip2 bzip2 cat chmod cmake cp date find flock	\
-			g++ gcc git grep gunzip gzip hostname id install kill	\
-			ln lzip make mkdir mkfifo mktemp mv paste patch perl	\
-			pgrep pkill printf readlink rm sed sha256sum sort	\
-			stat tail tar test touch tr uniq wget xz zip; then
+	if ! rtl_check_prereqs ${DEFAULT_PREREQS}; then
 		printf "%s\n" "${_status}" >&2; exit 1;
 	elif ! awk -V 2>/dev/null | grep -q "^GNU Awk "; then
 		printf "Error: awk(1) in \$PATH must be GNU Awk." >&2; exit 1;
-	elif ! (FNAME="$(mktemp)" && { trap "rm -f \"\${FNAME}\"" EXIT;		\
+	elif ! (FNAME="$(mktemp)" && { trap "rm -f \"\${FNAME}\"" EXIT;	\
 			sed -i'' -e '' "${FNAME}" >/dev/null 2>&1; }); then
 		printf "Error: sed(1) in \${PATH} does not support the \`-i' option.\n" >&2; exit 1;
 	fi;
@@ -378,8 +239,8 @@ build_init() {
 	local _rc=0; _status="";
 	if ! buildp_init_env			\
 	|| ! buildp_init_getopts "${@}"		\
-	|| ! buildp_init_prereqs		\
 	|| ! ex_pkg_load_vars			\
+	|| ! buildp_init_prereqs		\
 	|| ! buildp_init_args			\
 	|| ! buildp_init_files; then
 		_rc=1; _status="${_status}";
diff --git a/subr/ex_pkg_exec.subr b/subr/ex_pkg_exec.subr
index ee49b87d..f20c5c38 100644
--- a/subr/ex_pkg_exec.subr
+++ b/subr/ex_pkg_exec.subr
@@ -94,7 +94,7 @@ ex_pkg_exec() {
 		_rc=1;
 	elif rtl_test_cmd "pkg_${_pkg_name}_all"; then
 		"pkg_${_pkg_name}_all" "${_restart_at}"; _rc="${?}";
-	else	set -- $(rtl_lfilter "${PKG_BUILD_STEPS}" "start");
+	else	set -- ${PKG_BUILD_STEPS};
 		while [ ${#} -gt 0 ]; do
 			_step="${1}"; shift;
 			if [ "${#_restart_at}" -gt 0 ]\
diff --git a/subr/ex_pkg_restart.subr b/subr/ex_pkg_restart.subr
new file mode 100644
index 00000000..20e35b63
--- /dev/null
+++ b/subr/ex_pkg_restart.subr
@@ -0,0 +1,286 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+#
+# exp_pkg_check_restart_at() - XXX
+# @_rspec_at:		in reference to restart build step list
+#
+# Calling convention:	in ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_check_restart_at() {
+	local _epcra_rspec_at="${1#\$}" _epcra_len="" _epcra_rc=0 _epcra_spec_at=""; _status=""
+
+	if ! rtl_llift2 "${_epcra_rspec_at}" \$_epcra_spec_at "," " "\
+	|| ! rtl_lfilter3 \$_epcra_spec_at "${DEFAULT_BUILD_STEPS} ALL LAST"\
+	|| ! rtl_llength2 \$_epcra_spec_at \$_epcra_len; then
+		_epcra_rc=1;
+	elif [ "${_epcra_len}" -gt 0 ]; then
+		_status="unknown build step(s) \`${_epcra_spec_at}'"; _epcra_rc=1;
+	fi; return "${_epcra_rc}";
+};
+
+#
+# exp_pkg_expand_restart_at_spec() - XXX
+# @_rset:		in reference to restart virtual build step set
+# @_rspec_at:		inout reference to restart build step list
+#
+# Calling convention:	in ref. @_rset, inout ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_at_spec() {
+	local	_eperas_rset="${1#\$}" _eperas_rspec_at="${2#\$}" _eperas_at=""			\
+		_eperas_rc=0 _eperas_spec_at="" _eperas_spec_at_=""; _status="";
+	eval _eperas_spec_at='${'"${_eperas_rspec_at}"'}';
+
+	case "${_eperas_spec_at}" in
+	ALL|LAST|"")
+		;;
+
+	^*)
+		_eperas_spec_at="${_eperas_spec_at#^}";
+		if exp_pkg_expand_restart_at_virtual						\
+				"${_eperas_spec_at}" \$_eperas_spec_at				\
+				"${_eperas_rset}"						\
+		&& exp_pkg_check_restart_at \$_eperas_spec_at; then
+			rtl_llift2 \$DEFAULT_BUILD_STEPS "${_eperas_rspec_at}" " 	" ",";
+			rtl_llift2 \$_eperas_spec_at \$_eperas_spec_at_ "," " ";
+			for _eperas_at in ${_eperas_spec_at_}; do
+				rtl_lfilter3 "${_eperas_rspec_at}" "${_eperas_at}" ",";
+			done; rtl_lfilter3 "${_eperas_rspec_at}" "finish" ",";
+		else
+			_eperas_rc=1;
+		fi; ;;
+
+	\<=*|\<*|\>=*|\>*)
+		exp_pkg_expand_restart_at_spec_cmp						\
+			"${_eperas_rset}" "${_eperas_rspec_at}"; _eperas_rc="${?}"; ;;
+
+	*)
+		if ! exp_pkg_expand_restart_at_virtual						\
+				"${_eperas_spec_at}" "${_eperas_rspec_at}"			\
+				"${_eperas_rset}"; then
+			_eperas_rc=1;
+		fi; ;;
+	esac;
+
+	if [ "${_eperas_rc}" -eq 0 ]; then
+		if ! exp_pkg_check_restart_at "${_eperas_rspec_at}"; then
+			_epprs_rc=1;
+		elif eval [ '"${'"${_eperas_rspec_at}"':+1}"' != 1 ]; then
+			_status="zero-length build step list"; _epprs_rc=1;
+		fi;
+	fi;
+	return "${_eperas_rc}";
+};
+
+#
+# exp_pkg_expand_restart_at_spec_cmp() - XXX
+# @_rset:		in reference to restart virtual build step set
+# @_rspec_at:		inout reference to restart build step list
+#
+# Calling convention:	in ref. @_rset, inout ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_at_spec_cmp() {
+	local	_eperasc_rset="${1#\$}" _eperasc_rspec_at="${2#\$}" _eperasc_at=""		\
+		_eperasc_eqfl="" _eperasc_foundfl="" _eperasc_ltfl="" _eperasc_rc=0		\
+		_eperasc_spec_at="" _eperasc_spec_at0="";
+	eval _eperasc_spec_at0='${'"${_eperasc_rspec_at}"'}';
+
+	[ "${_eperasc_spec_at0#<}" = "${_eperasc_spec_at0}" ]; _eperasc_ltfl="${?}";
+	if [ "${_eperasc_spec_at0#[<>]=}" != "${_eperasc_spec_at0}" ]; then
+		_eperasc_spec_at0="${_eperasc_spec_at0#[<>]=}"; _eperasc_eqfl=1;
+	else
+		_eperasc_spec_at0="${_eperasc_spec_at0#[<>]}"; _eperasc_eqfl=0;
+	fi; _eperasc_spec_at="";
+
+	if exp_pkg_expand_restart_at_virtual							\
+			"${_eperasc_spec_at0%%,*}" \$_eperasc_spec_at0				\
+			"${_eperasc_rset}"							\
+	&& exp_pkg_check_restart_at \$_eperasc_spec_at0; then
+		if [ \( "${_eperasc_eqfl}" -eq 1 \) -a \( "${_eperasc_ltfl}" -eq 1 \) ]\
+		|| [ \( "${_eperasc_eqfl}" -eq 0 \) -a \( "${_eperasc_ltfl}" -eq 0 \) ]; then
+			_eperasc_spec_at0="${_eperasc_spec_at0##*,}";
+		elif [ \( "${_eperasc_eqfl}" -eq 1 \) -a \( "${_eperasc_ltfl}" -eq 0 \) ]\
+		||   [ \( "${_eperasc_eqfl}" -eq 0 \) -a \( "${_eperasc_ltfl}" -eq 1 \) ]; then
+			_eperasc_spec_at0="${_eperasc_spec_at0%%,*}";
+		fi;
+
+		_eperasc_foundfl=0; for _eperasc_at in ${DEFAULT_BUILD_STEPS}; do
+			if [ "${_eperasc_ltfl}" -eq 1 ]; then
+				if [ "${_eperasc_at}" = "${_eperasc_spec_at0%%,*}" ]; then
+					if [ "${_eperasc_eqfl}" -eq 1 ]; then
+						_eperasc_spec_at="${_eperasc_spec_at:+${_eperasc_spec_at},}${_eperasc_at}";
+					fi; break;
+				fi;
+			else
+				if [ "${_eperasc_at}" = "${_eperasc_spec_at0%%,*}" ]; then
+					_eperasc_foundfl=1; [ "${_eperasc_eqfl}" -eq 0 ] && continue;
+				fi; [ "${_eperasc_foundfl}" -eq 0 ] && continue;
+			fi;
+			_eperasc_spec_at="${_eperasc_spec_at:+${_eperasc_spec_at},}${_eperasc_at}";
+		done;
+	else
+		_eperasc_rc=1;
+	fi;
+
+	eval ${_eperasc_rspec_at}='${_eperasc_spec_at}';
+	return "${_eperasc_rc}";
+};
+
+#
+# exp_pkg_expand_restart_at_virtual() - XXX
+# @_spec_at:		restart build step list
+# @_rspec_at_new:	out reference to new restart build step list
+# @_rset:		inout reference to restart virtual build step set
+#
+# Calling convention:	inout ref. @_rspec_recursive
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_at_virtual() {
+	local	_epera_spec_at="${1}" _epera_rspec_at_new="${2#\$}" _epera_rset="${3#\$}"	\
+		_epera_at="" _epera_IFS0="${IFS:- 	}" _epera_rc=0 _epera_spec_at_new=""	\
+		IFS; _status="";
+
+	eval ${_epera_rspec_at_new}=;
+	IFS=","; set -- ${_epera_spec_at}; IFS="${_epera_IFS0}";
+	while [ "${#}" -gt 0 ]; do
+		_epera_at="${1}"; shift;
+		if [ "${_epera_at#@}" != "${_epera_at}" ]; then
+			_epera_at="${_epera_at#@}";
+			if [ "${_epera_at%[^0-9a-zA-Z_]*}" != "${_epera_at}" ]; then
+				_status="invalid virtual build step \`${_epera_at}'"; _epera_rc=1;
+			elif eval [ '"${'"${_epera_rset}${_epera_at}"':+1}"' = 1 ]; then
+				eval _epera_at='${'"${_epera_rset}${_epera_at}"'}';
+			else
+				_status="unknown virtual build step \`${_epera_at}'"; _epera_rc=1;
+			fi;
+		fi;
+		eval ${_epera_rspec_at_new}='${'"${_epera_rspec_at_new}"':+${'"${_epera_rspec_at_new}"'},}${_epera_at}';
+	done;
+	return "${_epera_rc}";
+};
+
+#
+# exp_pkg_expand_restart_recursive() - XXX
+# @_rspec:		inout reference to restart {specification,package name list}
+# @_rrecursive:		out reference to recursion flag
+#
+# Calling convention:	inout ref. @_rspec, out ref. @_rrecursive
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_recursive() {
+	local _eperr_rspec="${1#\$}" _eperr_rrecursive="${2#\$}" _eperr_spec=""; _status=""
+	eval _eperr_spec='${'"${_eperr_rspec}"'}';
+
+	case "${_eperr_spec}" in
+	\*\*\*[a-zA-Z]*)
+			eval ${_eperr_rspec}='${_eperr_spec#\*\*\*}' ${_eperr_rrecursive}=3; ;;
+	\*\*[a-zA-Z]*)	eval ${_eperr_rspec}='${_eperr_spec#\*\*}' ${_eperr_rrecursive}=2; ;;
+	\*[a-zA-Z]*)	eval ${_eperr_rspec}='${_eperr_spec#\*}' ${_eperr_rrecursive}=1; ;;
+	ALL)		eval ${_eperr_rrecursive}=2; ;;
+	LAST)		eval ${_eperr_rrecursive}=0; ;;
+	esac;
+	return 0;
+};
+
+#
+# exp_pkg_expand_restart_spec() - XXX
+# @_rspec:		inout reference to restart {specification,package name list}
+# @_rspec_at:		out reference to restart build step list
+#
+# Calling convention:	inout ref. @_rspec, out ref. @_rspec_at, out ref. @_rrecursive
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_spec() {
+	local	_epers_rspec="${1#\$}" _epers_rspec_at="${2#\$}" _epers_last_pkg=""	\
+		_epers_rc=0 _epers_spec="" _epers_spec_at="" _epers_spec_at0="";
+	eval _epers_spec='${'"${_epers_rspec}"'}';
+
+	case "${_epers_spec}" in
+	"")	eval ${_eppras_rspec_at}=; ;;
+	ALL)	eval ${_epers_rspec_at}=ALL; ;;
+	LAST|LAST:*)
+		case "${_epers_spec}" in
+		LAST)	eval ${_epers_rspec_at}=LAST; ;;
+		LAST:*)	eval ${_epers_rspec_at}='${_epers_spec#LAST:}'; ;;
+		esac;
+		if [ "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME:+1}" = 1 ]\
+		&& [ -e "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]; then
+			if read -r _epers_last_pkg <"${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}"\
+			&& rtl_fileop rm "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}"; then
+				eval ${_epers_rspec}='${_epers_last_pkg}';
+			else
+				_status="failed to read or clear status of last failed package \`${_epers_last_pkg}'"; _epers_rc=1;
+			fi;
+		else
+			_status="cannot rebuild last failed package"; _epers_rc=1;
+		fi; ;;
+
+	*:*)	eval ${_epers_rspec}='${_epers_spec%:*}' ${_epers_rspec_at}='${_epers_spec#*:}'; ;;
+	*)	eval ${_epers_rspec_at}= ${_epers_rspec_at}=ALL; ;;
+	esac;
+	return "${_epers_rc}";
+};
+
+#
+# exp_pkg_init_restart_at_virtual() - XXX
+# @_rset:		out reference to restart virtual build step set
+#
+# Calling convention:	out ref. @_rset
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_init_restart_at_virtual() {
+	local _eperav_rset="${1#\$}" _eperav_step="" _eperav_step_virtual="" _epera_steps="";
+
+	rtl_lfilter2 \$DEFAULT_BUILD_STEPS \$_epera_steps "finish";
+	for _eperav_step in ${_epera_steps}; do
+		_eperav_step_virtual="${_eperav_step%%_*}";
+		if eval [ '"${'"${_eperav_rset}${_eperav_step_virtual}"':+1}"' != 1 ]; then
+			eval ${_eperav_rset}='"${'"${_eperav_rset}"':+${'"${_eperav_rset}"'},}${_eperav_step_virtual}"';
+		fi;
+		eval ${_eperav_rset}${_eperav_step_virtual}='"${'"${_eperav_rset}${_eperav_step_virtual}"':+${'"${_eperav_rset}${_eperav_step_virtual}"'},}${_eperav_step}"';
+	done; return 0;
+};
+
+#
+# ex_pkg_process_restart_spec() - XXX
+# @_rspec:		inout reference to restart {specification,package name list}
+# @_rspec_at:		out reference to restart build step list
+# @_rrecursive:		out reference to restart recursion flag
+#
+# Calling convention:	inout ref. @_rspec, out ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+ex_pkg_process_restart_spec() {
+	local	_epprs_rspec="${1#\$}" _epprs_rspec_at="${2#\$}" _epprs_rrecursive="${3#\$}"	\
+		_epprs_at="" _epprs_rc=0 _epprs_spec_at_new="" _epprs_step="" _epprs_step1=""	\
+		_epprs_virtual_set=""; _status="";
+
+	if exp_pkg_init_restart_at_virtual \$_epprs_virtual_set					\
+	&& exp_pkg_expand_restart_spec "${_epprs_rspec}" \$_epprs_spec_at_new			\
+	&& exp_pkg_expand_restart_recursive "${_epprs_rspec}" "${_epprs_rrecursive}"		\
+	&& exp_pkg_expand_restart_at_spec \$_epprs_virtual_set \$_epprs_spec_at_new; then
+		eval ${_epprs_rspec_at}=;
+		for _epprs_at in ${DEFAULT_BUILD_STEPS}; do
+			if rtl_lmatch "${_epprs_at}" "${_epprs_spec_at_new}" ","; then
+				eval ${_epprs_rspec_at}='${'"${_epprs_rspec_at}"':+${'"${_epprs_rspec_at}"'},}${_epprs_at}';
+			fi;
+		done;
+		if eval [ '"${'"${_epprs_rspec_at}"'##*,}"' != "finish" ]; then
+			rtl_lfilter2 "${_epprs_rspec_at}" \$_epprs_step "clean,finish" ","; _epprs_step="${_epprs_step##*,}";
+			rtl_lfilter2 \$DEFAULT_BUILD_STEPS \$_epprs_step1 "clean finish"; _epprs_step1="${_epprs_step1##* }";
+			if [ "${_epprs_step}" = "${_epprs_step1}" ]; then
+				eval ${_epprs_rspec_at}='${'"${_epprs_rspec_at}"':+${'"${_epprs_rspec_at}"'},}finish';
+			fi;
+		fi;
+	else
+		_epprs_rc=1;
+	fi;
+	rtl_sunset \$_epprs_virtual_set;
+	return "${_epprs_rc}";
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_build_clean.subr b/subr/pkg_build_clean.subr
new file mode 100644
index 00000000..55dc19c5
--- /dev/null
+++ b/subr/pkg_build_clean.subr
@@ -0,0 +1,33 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_build_clean() {
+	local	_libtool="" _makeflags_verbosity="${PKG_MAKEFLAGS_VERBOSITY:-}"			\
+		_no_autoconf="" _rc=0 _subdir="";
+
+	if ex_pkg_state_test "${_pkg_name}" "build" "${_restart_at}"; then
+		case "${PKG_LIBTOOL:-}" in
+		"")	_libtool=""; ;;
+		none)	_libtool=""; ;;
+		*)	_libtool="${PKG_LIBTOOL}"; ;;
+		esac;
+		[ ! -x "${PKG_CONFIGURE:-}" ] && _no_autoconf=1;
+
+		for _subdir in ${PKG_MAKE_SUBDIRS:-:}; do
+			[ "${_subdir}" = ":" ] && _subdir="";
+			[ "${#_libtool}" -gt 0 ] && export MAKE="make LIBTOOL=${_libtool}";
+			rtl_run_cmd_unsplit "${PKG_MAKE}"					\
+				${PKG_MAKEFLAGS_BUILD:-}					\
+				${PKG_MAKEFLAGS_BUILD_EXTRA:-}					\
+				${_libtool:+"LIBTOOL=${_libtool}"}				\
+				${_makeflags_verbosity}						\
+				${_subdir:+-C "${_subdir}"}					\
+				clean; _rc="${?}";
+			[ "${#_libtool}" -gt 0 ] && unset MAKE;
+			[ "${_rc}" -ne 0 ] && return 1;
+		done; return 0;
+	fi;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_configure_clean.subr b/subr/pkg_configure_clean.subr
new file mode 100644
index 00000000..48549a90
--- /dev/null
+++ b/subr/pkg_configure_clean.subr
@@ -0,0 +1,20 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_configure_clean() {
+	local _group_name="${1}" _pkg_name="${2}" _restart_at="${3}";
+
+	if ex_pkg_state_test									\
+			"${_pkg_name}"								\
+			"configure_patch_pre,configure_autotools,configure_patch,configure"	\
+			"${_restart_at}"; then
+		if [ "${PKG_BUILD_DIR:-}" != "${PKG_SUBDIR:-}" ]; then
+			rtl_fileop rm "${PKG_BUILD_DIR}" || return 1;
+			rtl_fileop mkdir "${PKG_BUILD_DIR}" || return 1;
+			rtl_fileop cd "${PKG_BUILD_DIR}" || return 1;
+		fi;
+	fi;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_fetch_clean.subr b/subr/pkg_fetch_clean.subr
new file mode 100644
index 00000000..a56196cb
--- /dev/null
+++ b/subr/pkg_fetch_clean.subr
@@ -0,0 +1,21 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_fetch_clean() {
+	local _dname="";
+
+	if [ -n "${PKG_URLS_GIT:-}" ]; then
+		if [ -n "${PKG_SUBDIR:-}" ]\
+		&& [ "${PKG_SUBDIR}" != "${PKG_URLS_GIT%%=*}" ]; then
+			rtl_fileopm rm "${PKG_SUBDIR}";
+		fi;
+		for _dname in ${PKG_URLS_GIT}; do
+			_dname="${_dname%%=*}"; rtl_fileop rm "${_dname}";
+		done;
+	elif [ -n "${PKG_SUBDIR}" ]; then
+		rtl_fileop rm "${PKG_SUBDIR}";
+	fi; return 0;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_install_clean.subr b/subr/pkg_install_clean.subr
new file mode 100644
index 00000000..3d99f321
--- /dev/null
+++ b/subr/pkg_install_clean.subr
@@ -0,0 +1,12 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_install_clean() {
+	if [ -n "${PKG_DESTDIR:-}" ]; then
+		rtl_fileop rm "${PKG_DESTDIR}" || return 1;
+		rtl_fileop mkdir "${PKG_DESTDIR}" || return 1;
+	fi; return 0;
+};
+
+# vim:filetype=sh