Dialyxir - Recent Updates and Request for Feedback

I’d love to check this out in my phoenix app. Could you provide a simple list of “getting started” on a current phoenix app (v1.2)? I am fairly new to dialyzer, and I remember jose tweeting that with 1.2 it should be a good experience now.

Sure, it is really straightforward.

Assuming you’ve just generated a new Phoenix project.

Edit your mix.exs:

In deps add:

{:dialyxir, "~> 0.3.5"}

In project add:

dialyzer: [plt_add_deps: :transitive]

At the command line run:

mix do deps.get, deps.compile, dialyzer.plt

Now you are all set, you can run mix dialyzer anytime you want to check your project.

except…

Currently there are some spurious warnings in the default project. At least some of these will be fixed upstream, but for now you need to add a couple annotations to get rid of them.

Example file names for a project named myapp:

In lib/myapp/repo.ex add the @dialyzer attribute as below:

defmodule Myapp.Repo do
  use Ecto.Repo, otp_app: :myapp
  @dialyzer {:nowarn_function, rollback: 1}
end

Similarly, add this attribute in web/gettext.ex:

  @dialyzer [{:nowarn_function, 'MACRO-dgettext': 3},
             {:nowarn_function, 'MACRO-dgettext': 4},
             {:nowarn_function, 'MACRO-dngettext': 5},
             {:nowarn_function, 'MACRO-dngettext': 6},
            ]

The default PageView module (which includes web/page/index.html.eex) will emit the warning:
index.html.eex:1: The pattern {'safe', _@2} can never match the type binary()

Add @dialyzer :no_match to your PageView to resolve it.

web/views/page_view.ex

defmodule Myapp.PageView do
  use Chat.Web, :view
  @dialyzer :no_match
end

thank you very much! you should copy this to the github readme or a wiki page and link to it - I can imagine that there will be more folks that want to try dialyzer explicitly in phoenix

Good idea, I added a wiki page for it and put a plug for it in the Github readme.

I believe this is a Phoenix 1.2 bug. Didn’t yet try with 1.3 to see if it’s fixed. We’re still using 1.2 and just add @dialyzer :no_match in the view module, and a brief comment.

Aha, thanks Sasa! I had tried that but included :no_match in a tuple, oops!

Relatedly, can anyone clarify what differences exist between this library and dialyze ?

I think the main difference is that dialyze is controlled by command line switches, and dialyxir is driven more by configuration. dialyxir does take a couple of args, and you can pass any dialyzer arg and it gets passed on. dialyze is a single task and it will just do whatever is required to setup the PLT when you run it. When you are just doing analysis with dialyze you probably want to pass --no-check so that it doesn’t check for updated apps every time you analyze your project. With dialyxir you have to run the separate dialyzer.plt task to create/update/check the PLT. This lets it default to --no-check.

The implementations are also different; dialyze uses the erlang :dialyzer module to perform all operations. dialyxir builds a command-line string and shells out to dialyzer. It prints this string which is handy for debugging; several issues (usually user environment/project specific) that have been reported to the issue tracker I was able to figure out just by reading the command string it generated.

dialyxir was started first but probably lacked some features when dialyze came out. I think dialyze has had more sensible defaults, for example it has always included all direct dependencies in the PLT. I do not think it lets you change that though; dialyxir gives you full control of what goes in the PLT. The thing is I do not know if anyone wants that. dialyxir has lots of configuration and I have little idea of how much of it is used.

Instead of adding it to my 30+ *_view.ex modules I added it to the *.Web.view/1 with a TODO: to remind me to check if this has been fixed upstream yet and remove it if so. Much easier having it in one place, and it works.

Found another for your wiki page, Phoenix.Presence is also apparently bugged as this code:

  use Phoenix.Presence, otp_app: :my_server, pubsub_server: MyServer.PubSub # Line 75

Generates this dialyzer issue:

help_presence.ex:75: Expression produces a value of type {'ok',pid()}, but this value is unmatched
help_presence.ex:75: The inferred return type of init/1 ({'ok',#{}}) has nothing in common with {'error',_} | {'ok',pid()}, which is the expected return type for the callback of 'Elixir.Phoenix.Presence' behaviour
help_presence.ex:75: The inferred return type of track/3 ({'error',_} | {'ok',binary()}) has nothing in common with 'ok', which is the expected return type for the callback of 'Elixir.Phoenix.Presence' behaviour
help_presence.ex:75: The inferred return type of track/4 ({'error',_} | {'ok',binary()}) has nothing in common with 'ok', which is the expected return type for the callback of 'Elixir.Phoenix.Presence' behaviour
help_presence.ex:75: The inferred return type of update/3 ({'error',_} | {'ok',binary()}) has nothing in common with 'ok', which is the expected return type for the callback of 'Elixir.Phoenix.Presence' behaviour
help_presence.ex:75: The inferred return type of update/4 ({'error',_} | {'ok',binary()}) has nothing in common with 'ok', which is the expected return type for the callback of 'Elixir.Phoenix.Presence' behaviour

And this fixes most of them:

  @dialyzer [
              {:nowarn_function, 'init': 1},
              {:nowarn_function, 'track': 3},
              {:nowarn_function, 'track': 4},
              {:nowarn_function, 'update': 3},
              {:nowarn_function, 'update': 4},
            ]

However it leaves this:

help_presence.ex:75: Expression produces a value of type {'ok',pid()}, but this value is unmatched

And I am not sure what is happening here, any help? Is this one or the others my bug instead?