compat: Add compatibility defines for older GLib

We are already using a number of defines and autoptrs from newer GLib
releases. Add the appropriate compatibility defines rather than removing
the corresponding code.

Closes: #222

libfprint/drivers_api.h

@@ -21,6 +21,7 @@
 
 #pragma once
 
+#include "fpi-compat.h"
 #include "fpi-assembling.h"
 #include "fpi-device.h"
 #include "fpi-image-device.h"

libfprint/fp-print.c

@@ -21,6 +21,7 @@
 #define FP_COMPONENT "print"
 
 #include "fp-print-private.h"
+#include "fpi-compat.h"
 #include "fpi-log.h"
 
 /**

libfprint/fpi-compat.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2020 Benjamin Berg <bberg@redhat.com>
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#pragma once
+
+#include <glib-object.h>
+
+#if !GLIB_CHECK_VERSION (2, 57, 0)
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (GTypeClass, g_type_class_unref);
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (GEnumClass, g_type_class_unref);
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (GParamSpec, g_param_spec_unref);
+#else
+/* Re-define G_SOURCE_FUNC as we are technically not allowed to use it with
+ * the version we depend on currently. */
+#undef G_SOURCE_FUNC
+#endif
+
+#define G_SOURCE_FUNC(f) ((GSourceFunc) (void (*)(void))(f))

libfprint/fpi-context.h

@@ -20,6 +20,7 @@
 
 #include <gusb.h>
 #include "fp-context.h"
+#include "fpi-compat.h"
 
 /**
  * fpi_get_driver_types:

tests/test-fpi-device.c

@@ -22,6 +22,7 @@
 #define FP_COMPONENT "device"
 
 #include "fpi-device.h"
+#include "fpi-compat.h"
 #include "fpi-log.h"
 #include "test-device-fake.h"