tests: Add test for G_ALIGNOF()

To guarantee that its behaviour is always the same as the
G_STRUCT_OFFSET fallback.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://gitlab.gnome.org/GNOME/glib/issues/1055

glib/tests/Makefile.am

@@ -70,6 +70,7 @@ test_programs = \
 	keyfile				\
 	list				\
 	logging				\
+	macros				\
 	mainloop			\
 	mappedfile			\
 	markup				\

glib/tests/macros.c

@@ -0,0 +1,53 @@
+/* GLib testing framework examples and tests
+ *
+ * Copyright © 2018 Endless Mobile, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Philip Withnall <withnall@endlessm.com>
+ */
+
+#include <glib.h>
+
+/* Test G_ALIGNOF() gives the same results as the G_STRUCT_OFFSET fallback. This
+ * should be the minimal alignment for the given type.
+ *
+ * This is necessary because the implementation of G_ALIGNOF() varies depending
+ * on the compiler in use. We want all implementations to be consistent.
+ *
+ * In the case that the compiler uses the G_STRUCT_OFFSET fallback, this test
+ * is a no-op. */
+static void
+test_alignof_fallback (void)
+{
+#define check_alignof(type) \
+  g_assert_cmpint (G_ALIGNOF (type), ==, G_STRUCT_OFFSET (struct { char a; type b; }, b))
+
+  check_alignof (char);
+  check_alignof (int);
+  check_alignof (float);
+  check_alignof (double);
+  check_alignof (struct { char a; int b; });
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/alignof/fallback", test_alignof_fallback);
+
+  return g_test_run ();
+}

glib/tests/meson.build

@@ -38,6 +38,7 @@ glib_tests = {
   'keyfile' : {},
   'list' : {},
   'logging' : {},
+  'macros' : {},
   'mainloop' : {},
   'mappedfile' : {},
   'markup' : {},