+m4_ifvaln([$5], [AM_CONDITIONAL([$5], [test "x$sr_have_$1" = xyes])])[]dnl
+])
+
+## _SR_ARG_OPT_CHECK(sh-name, [features-var], opt-name, [cpp-name],
+## [cond-name], check-commands, [summary-result])
+##
+m4_define([_SR_ARG_OPT_CHECK],
+[dnl
+_SR_ARG_OPT_IMPL($@)
+sr_pkg_check_summary_append "$3" m4_default([$7], ["$sr_have_$1"])
+])
+
+## SR_ARG_OPT_CHECK(opt-name, [cpp-name], [cond-name], check-commands,
+## [summary-result = $sr_have_<opt-name>])
+##
+## Provide a --without-<opt-name> configure option for explicit disabling
+## of an optional dependency. If not disabled, the availability of the
+## optional dependency is auto-detected by running <check-commands>.
+##
+## The <check-commands> should set the shell variable sr_have_<opt-name>
+## to "yes" if the dependency is available, otherwise to "no". Optionally,
+## the <summary-result> argument may be used to generate a line in the
+## configuration summary. If supplied, it should be a shell word which
+## expands to the result to be displayed for the <opt-name> dependency.
+##
+## Use SR_VAR_OPT_PKG to generate lists of available modules and features.
+##
+AC_DEFUN([SR_ARG_OPT_CHECK],
+[dnl
+m4_assert([$# >= 4])[]dnl
+AC_REQUIRE([SR_PKG_CHECK_SUMMARY])[]dnl
+AC_REQUIRE([SR_VAR_OPT_PKG])[]dnl
+dnl
+_SR_ARG_OPT_CHECK(m4_expand([AS_TR_SH([$1])]),
+ m4_defn([_SR_VAR_OPT_PKG_FEATURES]),
+ $@)[]dnl
+])
+
+## _SR_ARG_OPT_PKG([features-var], [cond-name], opt-name,
+## [cpp-name], sh-name, [modules-var], module...)
+##
+m4_define([_SR_ARG_OPT_PKG],
+[dnl
+_SR_ARG_OPT_IMPL([$5], [$1], [$3], [$4], [$2],
+ [SR_PKG_CHECK(m4_shiftn([4], $@))])
+m4_ifvaln([$4], [AS_IF([test "x$sr_have_$5" = xyes],
+ [AC_DEFINE_UNQUOTED([CONF_$4_VERSION], ["$sr_$5_version"],
+ [Build-time version of $3.])])])[]dnl