[erlang-questions] Tricking dialyzer with an opaque type

[Paul Guyot]

Alex, Tobias,

Indeed, the function constructs the set using gb_sets API and then the result is embedded in the module with erl_parse:abstract/1.
The current solution consists in adding a call to an identity/1 function in the generated replacement code. This function is exported from the parse transform module of type fun(any()) -> any(). Since the parse transform is in another application, dialyzer seems to take its specification for granted (?). It's a cheaper equivalent of binary_to_term(term_to_binary(V)), although not free (it's still a remote call).

Paul

> On 30 Jun 2017, at 15:29, Alex S. <alex0player@REDACTED> wrote:
> 
> he is constructing it, after parse transform takes place.
>> 30 июня 2017 г., в 14:27, Tobias Lindahl <tobias.lindahl@REDACTED <mailto:tobias.lindahl@REDACTED>> написал(а):
>> 
>> It seems to me that the gb_sets:from_list/1 should give the correct type for your function even if the spec is not taken into account.
>> 
>> In that case, the value you are getting warnings for comes from somewhere else. Could it be that you are deconstructing the opaque type somewhere?
>> 
>> 
>> 2017-06-25 18:56 GMT+02:00 Paul Guyot <pguyot@REDACTED <mailto:pguyot@REDACTED>>:
>> Hello,
>> 
>> I do have a parse transform that replaces the body of a 0-arity function with its result, as evaluated at compile time.
>> I am looking for a way to avoid an opaque violation warning from dialyzer when this function returns, say, a gb_sets:set(). The spec is properly copied into the parsed tree, but dialyzer just ignores it.
>> 
>> Typically, such a function would load data from a file and create a gb_sets:set() from this data.
>> 
>> -spec f() -> gb_sets:set(unicode:unicode_binary()).
>> f() ->
>>         {ok, Content} = file:read_file(?FILENAME),
>>         List0 = binary:split(Content, <<"\n">>, [global]),
>>         List1 = lists:filter(fun(W) -> W =/= <<>> end, List0),
>>         gb_sets:from_list(List1).
>> 
>> With the parse_transform, dialyzer complains on usage, e.g. :
>> 
>> [warning] some_module.erl:123 the call gb_sets:add(<VALUE>,Var::{1..1114111,{_,_,_}}) does not have an opaque term of type gb_sets:set(_) as 2nd argument
>> 
>> Yet, of course, some_module.erl does not violate the opacity of gb_sets:set() itself.
>> I can trick dialyzer with an expensive identity function:
>> 
>>         gb_sets:add(Value, binary_to_term(term_to_binary(Var)))
>> 
>> Any better idea?
>> 
>> Paul
>> _______________________________________________
>> erlang-questions mailing list
>> erlang-questions@REDACTED <mailto:erlang-questions@REDACTED>
>> http://erlang.org/mailman/listinfo/erlang-questions <http://erlang.org/mailman/listinfo/erlang-questions>
>> 
>> _______________________________________________
>> erlang-questions mailing list
>> erlang-questions@REDACTED <mailto:erlang-questions@REDACTED>
>> http://erlang.org/mailman/listinfo/erlang-questions
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://erlang.org/pipermail/erlang-questions/attachments/20170630/8014d400/attachment.htm>