improvement: add allow_nil? to generic actions, defaults to false

lib/ash/action_input.ex

@@ -19,12 +19,15 @@ defmodule Ash.ActionInput do
   @type t :: %__MODULE__{
           arguments: map(),
           params: map(),
-          action: Ash.Resource.Actions.Action.t(),
+          action: Ash.Resource.Actions.Action.t() | nil,
           resource: Ash.Resource.t(),
           context: map(),
           api: Ash.Api.t(),
           valid?: boolean()
         }
+  def new(resource, api \\ nil) do
+    %__MODULE__{resource: resource, api: api}
+  end
 
   @doc """
   Creates a new input for a generic action
@@ -43,7 +46,8 @@ defmodule Ash.ActionInput do
           %__MODULE__{resource: resource, action: action}
 
         input ->
-          input
+          action = Ash.Resource.Info.action(input.resource, action)
+          %{input | action: action}
       end
 
     {input, _opts} = Ash.Actions.Helpers.add_process_context(input.api, input, opts)

lib/ash/actions/action.ex

@@ -120,6 +120,15 @@ defmodule Ash.Actions.Action do
 
                 {:error, error} ->
                   {:error, error}
+
+                other ->
+                  raise """
+                  Invalid return from generic action #{input.resource}.#{input.action.name}.
+
+                  Expected {:ok, result} or {:error, error}, got:
+
+                  #{inspect(other)}
+                  """
               end
 
             {:error, error} ->

lib/ash/resource/actions/action/action.ex

@@ -9,6 +9,7 @@ defmodule Ash.Resource.Actions.Action do
     constraints: [],
     touches_resources: [],
     arguments: [],
+    allow_nil?: false,
     transaction?: false,
     primary?: false,
     type: :action
@@ -19,6 +20,7 @@ defmodule Ash.Resource.Actions.Action do
           name: atom,
           description: String.t() | nil,
           arguments: [Ash.Resource.Actions.Argument.t()],
+          allow_nil?: boolean,
           touches_resources: [Ash.Resource.t()],
           constraints: Keyword.t(),
           run: {module, Keyword.t()},
@@ -41,6 +43,13 @@ defmodule Ash.Resource.Actions.Action do
                   Constraints for the return type. See the [constriants topic](/documentation/topics/constraints.md) for more.
                   """
                 ],
+                allow_nil?: [
+                  type: :boolean,
+                  default: false,
+                  doc: """
+                  Wether or not the action can return nil. Unlike attributes & arguments, this defaults to `false`.
+                  """
+                ],
                 run: [
                   type:
                     {:spark_function_behaviour, Ash.Resource.Actions.Implementation,