[erlang-bugs] Wrong dialyzer spec for erlang:process_info/2

[Patrik Nyblom]

On 10/19/2012 05:04 PM, Michał Ptaszek wrote:
> Hey,
>
> Let's define a function which is supposed to return us a list of links
> for a given process:
>
> -spec links(pid()) ->  [port() | pid()].
> links(Pid) ->
>      {links, Links} = process_info(Pid, links),
>      Links.
>
> Now let's run the dialyzer on the beam file:
>
> dialyzer -Wno_return -Wunderspecs --fullpath --plt .plt pi.beam
>    Checking whether the PLT .plt is up-to-date... yes
>    Proceeding with analysis...
> pi.erl:5: Type specification pi:links(pid()) ->  [port() | pid()] is a
> supertype of the success typing: pi:links(pid()) ->  [pid()]
>   done in 0m1.45s
> done (warnings were emitted)
>
> However it's clearly not right. For instance:
> (mynode@REDACTED)1>  erlang:process_info(whereis(erl_prim_loader), links).
> {links,[#Port<0.1>,<0.0.0>]}
>
> I wanted to fix it by myself, however could not find the right place
> to apply the patch. Where can I find specs for ERTS BIFs?
In master branch, they are in $ERL_TOP/erts/preloaded/src/erlang.erl

You need to do a ./otp_build update_preloaded --no-commit and then a 
make in $ERL_TOP to get it tested.

in maint branch, they are 'hardcoded' in erl_bif_types.erl in the hipe 
application. My recommendation is to *not* go there...
>
> Thanks,
> Michal
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Cheers,
/Patrik