The call does not have an opaque term of type 'Elixir.Ecto.Multi':t()

[wojtekmach]

Environment

• Elixir version (elixir -v): 1.8.0-dev
• Ecto version (mix deps): master

Current behavior

This code:

defmodule Dummy do
  def foo(%Ecto.Multi{} = multi) do
    Ecto.Multi.to_list(multi)
  end
end

raises following dialyzer error:

$ mix dialyzer --format=dialyxir
Finding suitable PLTs
Checking PLT...
[:compiler, :connection, :crypto, :db_connection, :decimal, :ecto, :elixir, :kernel, :logger, :poison, :poolboy, :postgrex, :stdlib]
PLT is up to date!
Starting Dialyzer
[
  check_plt: false,
  init_plt: '/Users/wojtek/src/elixir-ecto/dummy/_build/dev/dialyxir_erlang-21.0.9_elixir-1.8.0-dev_deps-dev.plt',
  files_rec: ['/Users/wojtek/src/elixir-ecto/dummy/_build/dev/lib/dummy/ebin'],
  warnings: [:unknown]
]
Total errors: 2, Skipped: 0
done in 0m0.9s
lib/dummy.ex:27:no_return
Function foo/1 has no local return.
________________________________________________________________________________
lib/dummy.ex:28:call_without_opaque
The call Ecto.Multi.to_list(_multi@1::#{'__struct__':='Elixir.Ecto.Multi', _=>_}) does not have an opaque term of type 'Elixir.Ecto.Multi':t() in 1.
________________________________________________________________________________

Since it's pretty common to pattern match on Multi struct, but not internals, should we change:

@opaque t :: %__MODULE__{operations: [{name, operation}], names: MapSet.t}

to:

@typep operations :: [{name, operation}]
@typep names :: MapSet.t
@type t :: %__MODULE__{operations: operations, names: names}

?

Expected behavior

no error.

cc @AndrewDryga