Why does dialyzer overlook this spec miss-match?

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1

Why is it that dialyzer doesn’t pick up on (obvious) miss-matches between @spec and implementation:

@spec example(Ecto.Changeset.t()) :: MySchema.t()
def example(changeset) do
    Repo.update(changeset)
end

I would expect it to complain since Repo.update is specced with {:ok, Ecto.Schema.t()} | {:error, Ecto.Changeset.t()} as it’s return value.

2

That is because the default implementation does not define the spec.

You can define it in your Repo module, and Dialyzer will complain.

defmodule Repo do
  use Ecto.Repo,
    otp_app: :your_app_name,
    adapter: Ecto.Adapters.Postgres

  @spec update(changeset :: Ecto.Changeset.t(), opts :: Keyword.t()) ::
          {:ok, Ecto.Schema.t()} | {:error, Ecto.Changeset.t()}
end

I guess you could submit a patch to Ecto fixing this.

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