Fix dialyzer warnings (#1691)

lib/livebook/application.ex

@@ -254,6 +254,8 @@ defmodule Livebook.Application do
     end
   end
 
+  @dialyzer {:no_return, iframe_port_in_use: 1}
+
   defp iframe_port_in_use(port) do
     Livebook.Config.abort!(
       "Failed to start Livebook iframe server because port #{port} is already in use"

lib/livebook/config.ex

@@ -132,7 +132,7 @@ defmodule Livebook.Config do
   @doc """
   Returns an mfa if there's a way to shut down the system.
   """
-  @spec shutdown_callback() :: mfa() | nil
+  @spec shutdown_callback() :: {module(), atom(), list()} | nil
   def shutdown_callback() do
     Application.fetch_env!(:livebook, :shutdown_callback)
   end

lib/livebook/notebook/cell/code.ex

@@ -13,7 +13,7 @@ defmodule Livebook.Notebook.Cell.Code do
 
   @type t :: %__MODULE__{
           id: Cell.id(),
-          source: String.t(),
+          source: String.t() | :__pruned__,
           outputs: list(Cell.indexed_output()),
           disable_formatting: boolean(),
           reevaluate_automatically: boolean()

lib/livebook/notebook/cell/markdown.ex

@@ -13,7 +13,7 @@ defmodule Livebook.Notebook.Cell.Markdown do
 
   @type t :: %__MODULE__{
           id: Cell.id(),
-          source: String.t()
+          source: String.t() | :__pruned__
         }
 
   @doc """

lib/livebook/notebook/cell/smart.ex

@@ -10,11 +10,11 @@ defmodule Livebook.Notebook.Cell.Smart do
 
   @type t :: %__MODULE__{
           id: Cell.id(),
-          source: String.t(),
+          source: String.t() | :__pruned__,
           chunks: Livebook.Runtime.chunks() | nil,
           outputs: list(Cell.indexed_output()),
-          kind: String.t(),
+          kind: String.t() | nil,
-          attrs: attrs(),
+          attrs: attrs() | :__pruned__,
           js_view: Livebook.Runtime.js_view() | nil,
           editor: Livebook.Runtime.editor() | nil
         }

lib/livebook/settings/env_var.ex

@@ -4,8 +4,8 @@ defmodule Livebook.Settings.EnvVar do
   import Ecto.Changeset
 
   @type t :: %__MODULE__{
-          name: String.t(),
+          name: String.t() | nil,
-          value: String.t()
+          value: String.t() | nil
         }
 
   @primary_key {:name, :string, autogenerate: false}

mix.exs

@@ -153,6 +153,8 @@ defmodule Livebook.MixProject do
     release
   end
 
+  @compile {:no_warn_undefined, Standalone}
+
   defp standalone_erlang_elixir(release) do
     Code.require_file("rel/app/standalone.exs")
 

test/support/test_modules/bad_inspect.ex

@@ -2,6 +2,8 @@ defmodule Livebook.TestModules.BadInspect do
   defstruct []
 
   defimpl Inspect do
+    @dialyzer {:nowarn_function, inspect: 2}
+
     def inspect(%Livebook.TestModules.BadInspect{}, _opts) do
       :bad_return
     end