class.c

static int
include_modules_at(const VALUE klass, VALUE c, VALUE module, int search_super)
{
    VALUE p, iclass;
    int method_changed = 0, constant_changed = 0;
    const st_table *const klass_m_tbl = RCLASS_M_TBL(RCLASS_ORIGIN(klass));

    while (module) {
	int superclass_seen = FALSE;

	if (RCLASS_ORIGIN(module) != module)
	    goto skip;
	if (klass_m_tbl && klass_m_tbl == RCLASS_M_TBL(module))
	    return -1;
	/* ignore if the module included already in superclasses */
	for (p = RCLASS_SUPER(klass); p; p = RCLASS_SUPER(p)) {
	    int type = BUILTIN_TYPE(p);
	    if (type == T_ICLASS) {
		if (RCLASS_M_TBL(p) == RCLASS_M_TBL(module)) {
		    if (!superclass_seen) {
			c = p;  /* move insertion point */
		    }
		    goto skip;
		}
	    }
	    else if (type == T_CLASS) {
		if (!search_super) break;
		superclass_seen = TRUE;
	    }
	}
	iclass = rb_include_class_new(module, RCLASS_SUPER(c));
	c = RCLASS_SET_SUPER(c, iclass);

	{
	    VALUE m = module;
	    if (BUILTIN_TYPE(m) == T_ICLASS) m = RBASIC(m)->klass;
	    rb_module_add_to_subclasses_list(m, iclass);
	}

	if (FL_TEST(klass, RMODULE_IS_REFINEMENT)) {
	    VALUE refined_class =
		rb_refinement_module_get_refined_class(klass);

	    st_foreach(RMODULE_M_TBL(module), add_refined_method_entry_i,
		       (st_data_t) refined_class);
	    FL_SET(c, RMODULE_INCLUDED_INTO_REFINEMENT);
	}
	if (RMODULE_M_TBL(module) && RMODULE_M_TBL(module)->num_entries)
	    method_changed = 1;
	if (RMODULE_CONST_TBL(module) && RMODULE_CONST_TBL(module)->num_entries)
	    constant_changed = 1;
      skip:
	module = RCLASS_SUPER(module);
    }

    if (method_changed) rb_clear_method_cache_by_class(klass);
    if (constant_changed) rb_clear_constant_cache();

    return method_changed;
}