Tell Autoconf to get the version from ddclient.in

This avoids the need to maintain the same version string in two
different places.

.autom4te.cfg

@@ -0,0 +1,6 @@
+# Disable autom4te cache to ensure that any change to ddclient.in triggers a
+# rebuild of the configure script (which gets the version of ddclient from
+# ddclient.in).  See <https://lists.gnu.org/r/automake/2019-10/msg00002.html>.
+begin-language: "Autoconf-without-aclocal-m4"
+args: --no-cache
+end-language: "Autoconf-without-aclocal-m4"

Makefile.am

@@ -76,6 +76,7 @@ generated_tests = \
 TESTS = $(handwritten_tests) $(generated_tests)
 $(TESTS): ddclient
 EXTRA_DIST += $(handwritten_tests) \
+	.autom4te.cfg \
 	t/lib/Devel/Autoflush.pm \
 	t/lib/Test/Builder.pm \
 	t/lib/Test/Builder/Formatter.pm \

configure.ac

@@ -1,5 +1,14 @@
 AC_PREREQ([2.63])
-AC_INIT([ddclient], [3.11.3_0])
+# Get the version from ddclient.in so that the same version string
+# doesn't have to be maintained in two places.  The m4_dquote macro is
+# used instead of quote characters to ensure that the command is only
+# run once.  The command outputs quote characters to prevent
+# incidental expansion (the m4_esyscmd macro does not quote the
+# command output itself, so the command output is subject to
+# expansion).
+AC_INIT([ddclient], m4_dquote(m4_esyscmd([printf '[%s]' "$(./ddclient.in --version=short)"])))
+# Needed because of the above invocation of ddclient.in.
+AC_SUBST([CONFIGURE_DEPENDENCIES], ['$(top_srcdir)/ddclient.in'])
 AC_CONFIG_SRCDIR([ddclient.in])
 AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_MACRO_DIR([m4])

t/version.pl.in

@@ -4,6 +4,6 @@ use version;
 SKIP: { eval { require Test::Warnings; } or skip($@, 1); }
 eval { require 'ddclient'; } or BAIL_OUT($@);
 
-is(ddclient->VERSION(), version->parse('v@PACKAGE_VERSION@'), "version matches Autoconf config");
+is($ddclient::version, '@PACKAGE_VERSION@', "version matches version in Autoconf");
 
 done_testing();