See this GitHub issue Passing a slot via attributes emits a warning (but still works) · Issue #3399 · phoenixframework/phoenix_live_view · GitHub.

Currently, it is possible to pass along a slot argument to another component, but not without the compiler emitting a warning.

The warning looks like this:

     warning: undefined attribute "loading" for component Phoenix.Component.async_result/1
     │
 133 │       I am a wrapper <.async_result assign={@assign} loading={@loading} inner_block={@inner_block} />

And here is an example of code that will induce the warning.

attr :assign, :any
slot :loading
slot :inner_block
def wrap_async_result(assigns) do
  ~H"""
  <div>
    I am a wrapper <.async_result assign={@assign} loading={@loading} inner_block={@inner_block} />
  </div>
  """
end

<.wrap_async_result assign={AsyncResult.loading()}>
  <:loading>Loading...</:loading>
  Finished
</.wrap_async_result>

Assuming attributes and slots will always share the same “namespace” (so there could not be an attribute and slot with the same name defined on a component), it seems useful to be able to pass a slot via attributes.

Are there any downsides I’m not considering?