Save static vegalite plot to livemd

lib/livebook/live_markdown/export.ex

@@ -153,6 +153,10 @@ defmodule Livebook.LiveMarkdown.Export do
     [delimiter, "output\n", text, "\n", delimiter]
   end
 
+  defp render_output({:vega_lite_static, vegalite_data}) do
+    ["```", "vega_lite_static\n", Jason.encode!(vegalite_data), "\n", "```"]
+  end
+
   defp render_output(_output), do: :ignored
 
   defp get_elixir_cell_code(%{source: source, disable_formatting: true}),

lib/livebook/live_markdown/import.ex

@@ -187,6 +187,16 @@ defmodule Livebook.LiveMarkdown.Import do
     take_outputs(ast, [output | outputs])
   end
 
+  defp take_outputs(
+         [{"pre", _, [{"code", [{"class", "vega_lite_static"}], [output], %{}}], %{}} | ast],
+         outputs
+       ) do
+    case Jason.decode(output) do
+      {:ok, data} -> take_outputs(ast, [{:vega_lite_static, data} | outputs])
+      _ -> take_outputs(ast, outputs)
+    end
+  end
+
   defp take_outputs(ast, outputs), do: {outputs, ast}
 
   # Builds a notebook from the list of elements obtained in the previous step.
@@ -198,7 +208,7 @@ defmodule Livebook.LiveMarkdown.Import do
   defp build_notebook([{:cell, :elixir, source, outputs} | elems], cells, sections, messages) do
     {metadata, elems} = grab_metadata(elems)
     attrs = cell_metadata_to_attrs(:elixir, metadata)
-    outputs = Enum.map(outputs, &{:text, &1})
+    outputs = Enum.map(outputs, fn output -> if is_tuple(output), do: output, else: {:text, output} end )
     cell = %{Notebook.Cell.new(:elixir) | source: source, outputs: outputs} |> Map.merge(attrs)
     build_notebook(elems, [cell | cells], sections, messages)
   end