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-common.h b/src/hb-common.h
index 4265bb3..df929ea 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -26,6 +26,10 @@
* Google Author(s): Behdad Esfahbod
*/
+#ifndef HB_H_IN
+#error "Include <hb.h> instead."
+#endif
+
#ifndef HB_COMMON_H
#define HB_COMMON_H
