Make it an error to include non-top-level headers
Users should #include <hb.h> (or hb-ft.h, hb-glib.h, etc), but
never things like hb-shape.h directly. This makes it easier to
refactor headers later on without breaking compatibility.
diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index 9582ebe..ca1bbf4 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -27,6 +27,10 @@
* Google Author(s): Behdad Esfahbod
*/
+#ifndef HB_H_IN
+#error "Include <hb.h> instead."
+#endif
+
#ifndef HB_BUFFER_H
#define HB_BUFFER_H
