Erlang edoc 多级目录出错

使用rebar doc来生成项目文档。
但是当erl源文件目录src下建立子目录，并新建erlang文件后，就无法生成文档。

例如，新建 src/tttt/, 并添加 dd_util.erl 文件。

D:\six>d:/tools/rebar/rebar.cmd doc
==> six (doc)
ERROR: doc failed while processing D:/six: {'EXIT',{function_clause,[{edoc,expan
d_sources,
                                [[{tttt,"dd_util.erl","./src/tttt"},
                                  {'',"gateway_http.erl","./src"},
                                  {'',"six.erl","./src"},
                                  {'',"six_app.erl","./src"},
                                  {'',"six_sup.erl","./src"}],
                                 ".erl",
                                 {set,0,16,16,8,80,48,
                                      {[],[],[],[],[],[],[],[],[],[],[],[],[],
                                       [],[],[]},
                                      {{[],[],[],[],[],[],[],[],[],[],[],[],
                                        [],[],[],[]}}},
                                 [],[]],
                                [{file,"edoc.erl"},{line,459}]},
                          {edoc,run,3,[{file,"edoc.erl"},{line,378}]},
                          {rebar_edoc,doc,2,
                                      [{file,"src/rebar_edoc.erl"},{line,63}]},
                          {rebar_core,run_modules,4,
                                      [{file,"src/rebar_core.erl"},
                                       {line,491}]},
                          {rebar_core,execute,6,
                                      [{file,"src/rebar_core.erl"},
                                       {line,416}]},
                          {rebar_core,maybe_execute,8,
                                      [{file,"src/rebar_core.erl"},
                                       {line,300}]},
                          {rebar_core,process_dir1,7,
                                      [{file,"src/rebar_core.erl"},
                                       {line,259}]},
                          {rebar_core,process_commands,2,
                                      [{file,"src/rebar_core.erl"},
                                       {line,91}]}]}}

D:\six>

在rebar.config中添加参数{packages, false}解决了。

{deps, [{mysql, ".*", {git, "https://github.com/dizzyd/erlang-mysql-driver.git"}},
        {lager, ".*",  {git, "https://github.com/basho/lager.git"}},  
        {mochiweb, ".*", {git, "https://github.com/mochi/mochiweb.git"}}]}.

{erl_opts, [{parse_transform, lager_transform}]}.

{edoc_opts, [{packages, false}]}.

大概是Erlang多层目录会建立“subpackages”，应该就是模块名字空间：
If the source code is organized in a hierarchy of subdirectories although it does not use packages, use no_packages
但是没有找到相关的文档，不知道如何建立子包。

参考：
http://www.erlang.org/documentation/doc-5.8.4/lib/edoc-0.7.8/doc/html/edoc.html#run-3
http://www.erlang.org/documentation/doc-5.8.4/lib/edoc-0.7.8/doc/html/chapter.html#Running_EDoc