Elixir 1.6 dialyzer GenServer issue

robinmonjo · November 9, 2017, 10:19pm

Hello all,

I have a problem with Elixir 1.6-dev and dialyzer on Supervisor / GenServer. Not sure if it’s a bug that I should report in a Github issue.

I created a new project (Elixir 1.6): mix new one_dot6 --sup, and followed this doc to add a GenServer supervised: https://hexdocs.pm/elixir/master/Supervisor.html

Then I setup Dialyxir, here is the full project: https://github.com/robinmonjo/one_dot6

When running mix dialyzer I’m getting this warning:

lib/gen_server.ex:581: The call 'Elixir.Supervisor':child_spec(_@2::#{'id':='Elixir.OneDot6.Stack', 'start':={'Elixir.OneDot6.Stack','start_link',[any(),...]}},[]) breaks the contract (child_spec() | {module(),arg::term()} | module(),elixir:keyword()) -> child_spec()

Spent lot’s of time on this and can’t figure it out … Should I open an issue on Github ?

Ryzey · January 30, 2018, 11:36pm

This seems to be related to this issue, which is now fixed in v1.6

github.com/jeremyjh/dialyxir

child_spec warnings with Elixir 1.6

opened 04:45PM - 10 Jan 18 UTC

closed 03:42AM - 11 Jan 18 UTC

micahrye

Not sure if this counts as an issue since Elixir 1.6 is still 1.6.0-rc.0. ##…# Using Elixir 1.6.0-rc.0 The issue is that when running 1.6.0-rc.0 dialyzer will produce warrnings if you do not explicitly define a `child_spec` when you use a GenServer, `use GenServer`. For example, given the following module that uses GenServer: ``` defmodule GenExample do use GenServer def start_link(_args) do GenServer.start_link(__MODULE__, [], name: __MODULE__) end def init(state) do {:ok, state} end end ``` If we run `$ mix dialyzer` we get the following: ``` mix dialyzer Compiling 1 file (.ex) Checking PLT... [:compiler, :elixir, :kernel, :logger, :stdlib] PLT is up to date! Starting Dialyzer dialyzer args: [ check_plt: false, init_plt: '/Users/micahrye/code/work/tulip/projects/elixir/sysfs/_build/dev/dialyxir_erlang-20.0_elixir-1.6.0-rc.0_deps-dev.plt', files_rec: ['/Users/micahrye/code/work/tulip/projects/elixir/sysfs/_build/dev/lib/sysfs/ebin'], warnings: [:unknown] ] done in 0m1.12s lib/gen_server.ex:2: Function child_spec/1 has no local return lib/gen_server.ex:581: The call 'Elixir.Supervisor':child_spec(_@2::#{'id':='Elixir.GenExample', 'start':={'Elixir.GenExample','start_link',[any(),...]}},[]) breaks the contract (child_spec() | {module(),arg::term()} | module(),elixir:keyword()) -> child_spec() done (warnings were emitted) ``` If we add a child_spec to our example module above: ``` defmodule GenExample do use GenServer def child_spec(arg) do %{ id: __MODULE__, start: {__MODULE__, :start_link, [arg]}, restart: :permanent, shutdown: 5000, type: :worker } end def start_link(_args) do GenServer.start_link(__MODULE__, [], name: __MODULE__) end def init(state) do {:ok, state} end end ``` Now `$ mix dialyzer` will `done (passed successfully)` ### Using Elixir 1.5.0 If we change nothing but use Elixir 1.5 you do not get the warnings, following is output from running dialyzer with and without explicitly defining `child_spec` ``` ... done (passed successfully) ```