[erlang-questions] Dialyzer underspecs and overspecs options

[Alex S.]

What you want is provided as a default behaviour. Overspecs you shouldn’t really enable for production needs, it’s «debug the Dialyzer» feature.


> 24 марта 2017 г., в 21:42, Dmitry Kakurin <dima_kakurin@REDACTED> написал(а):
> 
> Hi all,
> I've started using Dialyzer and tried to enable as many warnings as possible.
> Two of them that seem especially useful are underspecs and overspecs.
> But after struggling with warnings produced by them for a while I've realized that what I really need is a subset of each.
> In the example below (sorry, I'm using Elixir syntax but hope it's still obvious) the 2 warnings I want to enable are under_in and over_out. They are the ones that will break callers relying on the spec. While over_in and under_out warnings are more of a hints to the function author about current implementation and are much less serious.
> The current Dialyzer options allow me to enable either both over_* warnings or both under_* warnings. But that's not useful.
> Is there a way to configure Dialyzer the way I want?
> 
> Here is the demo code:
> 
>   # suboptimal implementation, fine for caller
>   @spec over_in(x :: integer) :: nil
>   def over_in(x) when is_number(x) do
>     nil
>   end
> 
>   # broken caller contract, could return unexpected value
>   @spec over_out(x :: number) :: integer
>   def over_out(x) when is_number(x) do
>     x
>   end
> 
>   # broken caller contract, rejects input allowed by the spec
>   @spec under_in(x :: number) :: nil
>   def under_in(x) when is_integer(x) do
>     nil
>   end
> 
>   # current implementation detail, does not concern caller
>   @spec under_out(x :: integer) :: number
>   def under_out(x) when is_integer(x) do
>     x
>   end
> 
> and here are the warnings:
> 
> demo.ex:4: Type specification
> 'Elixir.Virt':over_in(x::integer()) -> 'nil' is a subtype of the success typing: 
> 'Elixir.Virt':over_in(number()) -> 'nil'
> 
> demo.ex:9: Type specification
> 'Elixir.Virt':over_out(x::number()) -> integer() is a subtype of the success typing:
> 'Elixir.Virt':over_out(number()) -> number()
> 
> demo.ex:14: Type specification
> 'Elixir.Virt':under_in(x::number()) -> 'nil' is a supertype of the success typing:
> 'Elixir.Virt':under_in(integer()) -> 'nil'
> 
> demo.ex:19: The specification for 'Elixir.Virt':under_out/1 states that the function might also return
> float() but the inferred return is
> integer()
> 
> Thanks, Dmitry.
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