Dialyzer and exported types

Questions / Help
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1

I recently made a project with cowboy as a dependency and I used cowboy_req:req/0 type in my own specs. When I run dialyzer on the project I get the following errors:

_build/default/lib/cowboy/src/cowboy_req.erl
Line 134 Column 9: Unknown type ranch:ref/0
Line 152 Column 18: Unknown type ranch_proxy_header:proxy_info/0

Both types exist and are exported from ranch module.

Problem disappears when I add ranch in my .app file, but shouldn’t dialyzer handle that as ranch is the dependency of cowboy? Is that expected behavior or is it a bug?

I’m using cowboy 2.12.0 and rebar3 3.23.0 on OTP 27.0.0

1 Like
2

I have also noticed this. It started in Erlang 26 iirc.

3

What changed in OTP 26 is that unknown types are mentioned every time by dialyzer. By default rebar3 only analyzes top-level apps and top-level deps.

To analyze the whole project, configure dialyzer with:

{dialyzer, [
    {plt_apps, all_deps},
    …
]}.

You can also see at Base Config | Rebar3 that you can specify only particular apps to add with the extra option. You can also turn off the OTP 26 behavior by passing in the no_unknown warning option.

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