Add common/array.h with wl_array_len()

include/common/array.h

@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LABWC_ARRAY_H
+#define LABWC_ARRAY_H
+#include <wayland-server-core.h>
+
+/*
+ * Wayland's wl_array API is a bit sparse consisting only of
+ *  - init
+ *  - release
+ *  - add
+ *  - copy
+ *  - for_each
+ *
+ * The purpose of this header is the gather any generic wl_array helpers we
+ * create.
+ *
+ * We take the liberty of using the wl_ suffix here to make it look a bit
+ * prettier. If Wayland extend the API in future, we will sort the clash then.
+ */
+
+/**
+ * wl_array_len() - return length of wl_array
+ * @array: wl_array for which to calculate length
+ * Note: The pointer type might not be 'char' but this is the approach that
+ * wl_array_for_each() takes, so we align with their style.
+ */
+static inline size_t
+wl_array_len(struct wl_array *array)
+{
+	return array->size / sizeof(const char *);
+}
+
+#endif /* LABWC_ARRAY_H */