It looks like the function signature for put_layout/2 has changed from v1.6 to v1.7 such that the second argument now expects a keyword list that includes format :: atom() as the first item in each tuple.

put_layout/2 in v1.6:

@spec put_layout(
  Plug.Conn.t(),
  {atom(), binary() | atom()} | atom() | binary() | false
) ::
  Plug.Conn.t()

conn = put_layout conn, {AppView, "application.html"}
conn = put_layout conn, "print.html"

put_layout/2 in v1.7:

@spec put_layout(
  Plug.Conn.t(),
  [{format :: atom(), layout()}] | false
) ::
  Plug.Conn.t()

conn = put_layout(conn, html: {AppView, :application})
conn = put_layout(conn, html: :print)

Maybe try something like this:

pipeline :guest_layout do
	plug :put_layout, [html: {PhxAppWeb.LayoutView, :guest}]
end

I wanted to have a different layout for certain live view pages and I ended up modifying the my_app_web.ex file so that in my live views I could do this use MyAppWeb, {:live_view, layout: :home}. I do wonder if someone has a different approach though?

You could try scopes that pipe through different Router plugs like what @silverdr was doing.

defmodule HelloWeb.Router do
  use HelloWeb, :router

  pipeline :guest_layout do
    plug :put_layout, [html: {HelloWeb.LayoutView, :guest}]
  end

  pipeline :admin_layout do
    plug :put_layout, [html: {HelloWeb.LayoutView, :admin}]
  end

  scope "/guest", HelloWeb do
    pipe_through [:guest_layout]
    live "/feed", HelloWeb.FeedLive, :index
    live "/status", HelloWeb.StatusLive, :index
    live "/status/:id", HelloWeb.StatusLive, :show
  end
  
  scope "/admin", HelloWeb do
    pipe_through [:admin_layout]
    live "/admin", HelloWeb.AdminDashboardLive, :index
    live "/admin/posts", HelloWeb.AdminPostLive, :index
  end
end

Poking around the LiveView docs, I see there’s also a live_session/3 function for grouping together live routes into a session for live redirects which happens to accept an optional layout in the form of “a tuple with the view module and template string or atom name”.

defmodule HelloWeb.Router do
  use HelloWeb, :router

  live_session :guest, layout: {HelloWeb.LayoutView, :guest} do
    live "/feed", HelloWeb.FeedLive, :index
    live "/status", HelloWeb.StatusLive, :index
    live "/status/:id", HelloWeb.StatusLive, :show
  end

  live_session :admin, layout: {HelloWeb.LayoutView, :admin} do
    live "/admin", HelloWeb.AdminDashboardLive, :index
    live "/admin/posts", HelloWeb.AdminPostLive, :index
  end
end

Excellent replies @codeanpeace.

I have pushed a commit to LiveView that improves its docs: Improve layout docs · phoenixframework/phoenix_live_view@5ef4153 · GitHub

For regular controllers (put_layout) both old and new styles should be supported, this means your code should work @silverdr. Please open up a bug report with reproduction steps if it does not.

It was a combination of factors that caused some confusion. Actually the original style works. The reason for it not working was elsewhere but since LS reported that Function guest_layout/2 has no local return it looked like the old style no longer working. When I change to the new style though, the Dialyzer warning disappears, but… the pipeline becomes ineffective. IOW - this:

	pipeline :guest_layout do
		plug :put_layout, {PhxAppWeb.LayoutView, :guest}
	end

works despite the warning being emitted, while changing it to:

	pipeline :guest_layout do
		plug :put_layout, [html: {PhxAppWeb.LayoutView, :guest}]
	end

makes the warning go away together with the functionality of changing the layout. Any clues? The layout and view is a DeadView if this makes any difference.