GLib tests: Add test for g_win32_clear_com()

This mimicks the test for g_clear_object() in gobject/tests/reference.c.

We use the system's wincodec library for our sample here.

glib/tests/meson.build

@@ -246,7 +246,9 @@ if host_machine.system() == 'windows'
     }
   endif
   glib_tests += {
-    'win32' : {},
+    'win32' : {
+      'dependencies' : [wincodecs],
+    },
   }
 else
   glib_tests += {

glib/tests/win32.c

@@ -28,6 +28,9 @@
 #include <stdio.h>
 #include <windows.h>
 
+#define COBJMACROS
+#include <wincodec.h>
+
 static char *argv0 = NULL;
 
 #include "../gwin32-private.c"
@@ -154,6 +157,27 @@ veh_debugger (int argc, char *argv[])
   g_fprintf (stderr, "Debugger invoked, attaching to %lu and signalling %" G_GUINTPTR_FORMAT, pid, event);
 }
 
+static void
+test_clear_com (void)
+{
+  IWICImagingFactory *o = NULL;
+  IWICImagingFactory *tmp;
+
+  CoInitialize (NULL);
+  g_win32_clear_com (&o);
+  g_assert_null (o);
+  g_assert_true (SUCCEEDED (CoCreateInstance (&CLSID_WICImagingFactory, NULL, CLSCTX_INPROC_SERVER, &IID_IWICImagingFactory, (void **)&tmp)));
+  g_assert_nonnull (tmp);
+  IWICImagingFactory_QueryInterface (tmp, &IID_IWICImagingFactory, (void **)&o); /* IWICImagingFactory_QueryInterface increments the refcount */
+  g_assert_nonnull (o);
+  g_assert_cmpint (IWICImagingFactory_AddRef (o), ==, 3); /* refcount incremented again */
+  g_win32_clear_com (&o);
+  g_assert_null (o);
+  IWICImagingFactory_Release (tmp);
+
+  CoUninitialize ();
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -177,6 +201,7 @@ main (int   argc,
   g_test_add_func ("/win32/subprocess/debuggee", test_veh_debuggee);
   g_test_add_func ("/win32/subprocess/access_violation", test_access_violation);
   g_test_add_func ("/win32/subprocess/illegal_instruction", test_illegal_instruction);
+  g_test_add_func ("/win32/com/clear", test_clear_com);
 
   return g_test_run();
 }

meson.build

@@ -2338,8 +2338,11 @@ endif
 
 if host_system == 'windows'
   winsock2 = cc.find_library('ws2_32')
+  # Used for g_win32_clear_com() tests...
+  wincodecs = cc.find_library('windowscodecs')
 else
   winsock2 = not_found
+  wincodecs = not_found
 endif
 
 selinux_dep = []