[erlang-questions] Tricking dialyzer with an opaque type

[Paul Guyot]

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