Function harfbuzz_ft_sys::hb_ft_font_set_funcs

pub unsafe extern "C" fn hb_ft_font_set_funcs(font: *mut hb_font_t)

Official harfbuzz documentaion:

Makes an hb_font_t use FreeType internally to implement font functions. Note: this internally creates an FT_Face. Use it when you create your hb_face_t using hb_face_create().