desktop: add a test for strict validation of appdata file.

This way we can be warned quickly about any AppStream issue (cf. bug
782759). This test requires web access for screenshot verification.
Packagers are invited to use --without-appdata-test option if they want
to skip the test (for instance if build environment has restricted
network access).

configure.ac

@@ -2196,6 +2196,26 @@ if test "x$with_xvfb_run" != "xno"; then
 fi
 AM_CONDITIONAL(HAVE_XVFB_RUN, test "x$have_xvfb_run" = "xyes")
 
+##########################
+# Check for appstream-util
+##########################
+
+AC_ARG_WITH(appdata-test,  [  --without-appdata-test  do not validate the appdata file])
+
+have_appstream_util="no (disabled)"
+if test "x$with_appdata_test" != "xno"; then
+  AC_PATH_PROG(APPSTREAM_UTIL, appstream-util, no)
+  if test "x$APPSTREAM_UTIL" != "xno"; then
+    have_appstream_util="yes"
+  else
+    have_appstream_util="no (appstream-util not found)"
+  fi
+fi
+AM_CONDITIONAL(HAVE_APPSTREAM_UTIL, test "x$have_appstream_util" = "xyes")
+if test "x$have_appstream_util" = "xyes"; then
+  have_appstream_util="yes (this test requires network access; --without-appdata-test to disable)"
+fi
+
 
 ######################################
 # Checks for gtk-doc and docbook-tools
@@ -2656,6 +2676,7 @@ Optional Modules:
 
 Tests:
   Use xvfb-run         $have_xvfb_run
+  Test appdata         $have_appstream_util
 $have_recommended_xgettext$have_recommended_fontconfig$have_recommended_gtk$warning_vector_icons_windows$warning_glib_networking"
 
 if test "x$required_deps" = "x"; then

desktop/Makefile.am

@@ -67,3 +67,8 @@ validate: gimp.desktop
           fi )
 
 dist-hook: validate
+
+if HAVE_APPSTREAM_UTIL
+TESTS_ENVIRONMENT = GIMP_TESTING_ABS_TOP_SRCDIR=@abs_top_srcdir@
+TESTS = test-appdata.sh
+endif

desktop/test-appdata.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+appstream-util validate-strict ${GIMP_TESTING_ABS_TOP_SRCDIR}/desktop/gimp.appdata.xml.in