"undefined function assigns/0" while trying to use Phoenix.LiveViewTest.rendered_to_string/1

[maxmarcon]

Environment

• Elixir version (elixir -v): 1.13
• Phoenix version (mix deps): 1.6.4
• Phoenix LiveView version (mix deps): 0.17.5
• Operating system: MacOS 12.0.1

Actual behavior

Just trying out rendered_to_string (https://hexdocs.pm/phoenix_live_view/Phoenix.LiveViewTest.html#rendered_to_string/1) in iex -S mix, using the very same example as in the docs (nevermind the typo in the function name in the docs):

import Phoenix.LiveView.Helpers
iex(2)> ~H"""                                         
...(2)> <div>example</div>                             
...(2)> """ |> Phoenix.LiveViewTest.rendered_to_string

Expected behavior

As in the docs: <div>example</div>

Actual behavior

warning: variable "assigns" does not exist and is being expanded to "assigns()", please use parentheses to remove the ambiguity or change the variable name
  iex:2

** (CompileError) iex:2: undefined function assigns/0 (there is no such import)
    (elixir 1.13.0) src/elixir_fn.erl:17: anonymous fn/4 in :elixir_fn.expand/4
    (stdlib 3.15.2) lists.erl:1358: :lists.mapfoldl/3
    (elixir 1.13.0) src/elixir_fn.erl:23: :elixir_fn.expand/4
    (phoenix_live_view 0.17.5) expanding macro: Phoenix.LiveView.Helpers.sigil_H/2
    iex:2: (file)
    (elixir 1.13.0) expanding macro: Kernel.|>/2
    iex:4: (file)

I've actually discovered this while trying to use rendered_to_string in a live component test.

Is this a bug or am I forgetting something basic?

[josevalim]

I will see if I can improve the error message here but you always need to have an assigns variable set before using the ~H sigilx

[maxmarcon]

Thanks @josevalim. Yeah I'm aware that ~H needs assigns to be defined. However, I thought something might have changed when I came across these examples in the docs today on how to test function components: https://hexdocs.pm/phoenix_live_view/Phoenix.LiveViewTest.html#module-testing-function-components

import Phoenix.LiveView.Helpers
import Phoenix.LiveViewTest

test "greets" do
  assert rendered_to_string(~H"""
         <MyComponents.greet name="Mary" />
         """) ==
           "<div>Hello, Mary!</div>"
end

This wouldn't work, right? Something that might work instead would be:

import Phoenix.LiveView.Helpers
import Phoenix.LiveViewTest

test "greets" do
  assigns = []
  assert rendered_to_string(~H"""
         <MyComponents.greet name="Mary" />
         """) ==
           "<div>Hello, Mary!</div>"
end

So the docs need to be updated as far as I can see. I can come up with a little PR if you agree.

[josevalim]

Please send a PR for the docs, totally!

[maxmarcon]

PR is there