[erlang-questions] Dialyzer warning

[Fernando "Brujo" Benavides]

Oh! That was a tricky one!

Thanks Kostis :)

On 23/09/2011, at 13:17, Kostis Sagonas wrote:

> On 09/23/11 18:34, Fernando "Brujo" Benavides wrote:
>> Hi everybody,
>> 
>> I have a question that's mainly for Kostis, but maybe there're other out
>> there that had faced similar problems before.
>> I run dialyzer against the binaries of this project
>> <https://github.com/inaka/match_stream> as it's shown in its Makefile
>> <https://github.com/inaka/match_stream/blob/master/Makefile> and I get:
>> 
>>> match_stream_user_mgr.erl:32: The specification for
>>> match_stream_user_mgr:init/1 states that the function might also
>>> return
>>> {'ok',{{'simple_one_for_one',100,1},[{'match_stream_user',{'match_stream_user','start_link',[]},'transient','brutal_kill','worker',['match_stream_user']}]}}
>>> but the inferred return is none()
>>> match_stream_user_mgr.erl:33: Function init/1 has no local return
>> 
>> You can check match_stream_user_mgr:init/1
>> <https://github.com/inaka/match_stream/blob/master/src/match_stream_user_mgr.erl>
>> code... it's fairly simple:
>> 
>> 
>>> -spec init([]) -> {ok, {{simple_one_for_one, 100, 1},
>>> [{match_stream_user, {match_stream_user, start_link, []}, transient,
>>> brutal_kill, worker, [match_stream_user]}]}}.
>>> init([]) ->
>>> {ok, {{simple_one_for_one, 100, 1},
>>> [{match_stream_user, {match_stream_user, start_link, []},
>>> transient, brutal_kill, worker, [match_stream_user]}]}}.
>> 
>> Any clues?
> 
> Fernando,
> 
> In the code of your file you are including file "match_stream.hrl" (unnecessarily? because it is not used anywhere) which has the following record declaration:
> 
> -record(match_stream_user, {user_id :: match_stream:user_id(),
>                            visit_count = 1 :: pos_integer()}).
> 
> This tells dialyzer that all 3-tuples tagged with the atom 'match_stream_user' are intended to have a match_stream:user_id() in the second element and a pos_integer() in the third element of the tuple.
> 
> Still, in the file you are constructing the following 3-tuple:
> 
> 	{match_stream_user, start_link, []}
> 
> which violates the record definition (on the 3rd element).
> 
> You cannot have both.  You have three options:
> 
> 1. Take out the include declaration
> 2. Use a different tag for the tuple that you construct in the file
> 3. Add the [] in the type of the visit_count field
> 
> The first option is the easiest; the second is most probably the thing you want to do here.
> 
> Kostis
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