Add 'Render ... Markdown blocks' option to published apps

> Disclaimer: it's a proof-of-a-concept for an idea discussion.

It's an attempt to introduce a "Render ... Markdown blocks" feature to
the published apps as an option. It shall consider to render markdown
block from the original notebook as an addition to the evaluable cells.

Due to the limited understanding of how app rendering pipeline works,
this commit should be considered only as a proof-of-a-concept, that most
likely will be reworked fully.

P.S. Eventually, it should also take image and section titles cells and
render them.

lib/livebook/notebook/app_settings.ex

@@ -14,7 +14,8 @@ defmodule Livebook.Notebook.AppSettings do
           access_type: access_type(),
           password: String.t() | nil,
           show_source: boolean(),
-          output_type: output_type()
+          output_type: output_type(),
+          render_static: boolean()
         }
 
   @type access_type :: :public | :protected
@@ -33,6 +34,7 @@ defmodule Livebook.Notebook.AppSettings do
     field :password, :string
     field :show_source, :boolean
     field :output_type, Ecto.Enum, values: [:all, :rich]
+    field :render_static, :boolean
   end
 
   @doc """
@@ -49,7 +51,8 @@ defmodule Livebook.Notebook.AppSettings do
       access_type: :protected,
       password: generate_password(),
       show_source: false,
-      output_type: :all
+      output_type: :all,
+      render_static: false
     }
   end
 
@@ -82,14 +85,16 @@ defmodule Livebook.Notebook.AppSettings do
       :auto_shutdown_ms,
       :access_type,
       :show_source,
-      :output_type
+      :output_type,
+      :render_static
     ])
     |> validate_required([
       :slug,
       :multi_session,
       :access_type,
       :show_source,
-      :output_type
+      :output_type,
+      :render_static
     ])
     |> validate_format(:slug, ~r/^[a-z0-9-]+$/,
       message: "should only contain lowercase alphanumeric characters and dashes"

lib/livebook/notebook/cell.ex

@@ -49,6 +49,13 @@ defmodule Livebook.Notebook.Cell do
   def evaluable?(%Cell.Smart{}), do: true
   def evaluable?(_cell), do: false
 
+  @doc """
+  Checks if the given cell can be statically rendered
+  """
+  @spec static?(t()) :: boolean()
+  def static?(%Cell.Markdown{}), do: true
+  def static?(_), do: false
+
   @doc """
   Extracts all inputs from the given indexed output.
   """

lib/livebook_web/live/app_session_live.ex

@@ -442,17 +442,42 @@ defmodule LivebookWeb.AppSessionLive do
   defp data_to_view(data) do
     changed_input_ids = Session.Data.changed_input_ids(data)
 
-    %{
-      notebook_name: data.notebook.name,
-      cell_views:
-        for {cell, _section} <- Notebook.evaluable_cells_with_section(data.notebook) do
+    shall_render = fn cell ->
+      if data.notebook.app_settings.render_static do
+        Cell.evaluable?(cell) or Cell.static?(cell)
+      else
+        Cell.evaluable?(cell)
+      end
+    end
+
+    cell_views =
+      data.notebook
+      |> Notebook.cells_with_section()
+      |> Enum.filter(fn {cell, _section} -> shall_render.(cell) end)
+      |> Enum.map(fn
+        {%Livebook.Notebook.Cell.Markdown{} = cell, _section} ->
+          out_id = :rand.uniform(31337)
+          output = {out_id, %{type: :markdown_static, text: cell.source, chunk: false}}
+
+          %{
+            id: cell.id,
+            input_views: [],
+            outputs: [output],
+            outputs_batch_number: 0
+          }
+
+        {cell, _section} ->
           %{
             id: cell.id,
             input_views: input_views_for_cell(cell, data, changed_input_ids),
             outputs: filter_outputs(cell.outputs, data.notebook.app_settings.output_type),
             outputs_batch_number: data.cell_infos[cell.id].eval.outputs_batch_number
           }
-        end,
+      end)
+
+    %{
+      notebook_name: data.notebook.name,
+      cell_views: cell_views,
       app_status: data.app_data.status,
       show_source: data.notebook.app_settings.show_source,
       slug: data.notebook.app_settings.slug,

lib/livebook_web/live/output.ex

@@ -64,6 +64,19 @@ defmodule LivebookWeb.Output do
     """
   end
 
+  defp render_output(%{type: :markdown_static} = output, %{id: id, session_id: session_id}) do
+    assigns = %{id: id, session_id: session_id, output: output}
+
+    ~H"""
+    <.live_component
+      module={Output.MarkdownStaticComponent}
+      id={@id}
+      session_id={@session_id}
+      output={@output}
+    />
+    """
+  end
+
   defp render_output(%{type: :image} = output, %{id: id}) do
     assigns = %{id: id, content: output.content, mime_type: output.mime_type}
 

lib/livebook_web/live/output/markdown_static_component.ex

@@ -0,0 +1,12 @@
+defmodule LivebookWeb.Output.MarkdownStaticComponent do
+  use LivebookWeb, :live_component
+
+  @impl true
+  def render(assigns) do
+    ~H"""
+    <div>{to_html(@output.text)}</div>
+    """
+  end
+
+  defp to_html(markdown), do: Earmark.as_html!(markdown) |> Phoenix.HTML.raw()
+end

lib/livebook_web/live/session_live/app_settings_component.ex

@@ -105,6 +105,17 @@ defmodule LivebookWeb.SessionLive.AppSettingsComponent do
               '''
             }
           />
+          <.checkbox_field
+            field={f[:render_static]}
+            label="Render sections and Markdown blocks"
+            help={
+              ~S'''
+              When enabled, renders all the added
+              h2-sections and Markdown blocks of
+              the original notebook.
+              '''
+            }
+          />
           <%= if Ecto.Changeset.get_field(@changeset, :multi_session) do %>
             <.checkbox_field
               field={f[:show_existing_sessions]}

mix.exs

@@ -114,7 +114,7 @@ defmodule Livebook.MixProject do
       {:bandit, "~> 1.0"},
       {:plug, "~> 1.16"},
       {:plug_crypto, "~> 2.0"},
-      {:earmark_parser, "~> 1.4"},
+      {:earmark, "~> 1.4"},
       {:ecto, "~> 3.10"},
       {:phoenix_ecto, "~> 4.4"},
       {:aws_credentials, "~> 0.3.0", runtime: false},

mix.lock

@@ -9,6 +9,7 @@
   "cowlib": {:hex, :cowlib, "2.13.0", "db8f7505d8332d98ef50a3ef34b34c1afddec7506e4ee4dd4a3a266285d282ca", [:make, :rebar3], [], "hexpm", "e1e1284dc3fc030a64b1ad0d8382ae7e99da46c3246b815318a4b848873800a4"},
   "decimal": {:hex, :decimal, "2.1.1", "5611dca5d4b2c3dd497dec8f68751f1f1a54755e8ed2a966c2633cf885973ad6", [:mix], [], "hexpm", "53cfe5f497ed0e7771ae1a475575603d77425099ba5faef9394932b35020ffcc"},
   "dns_cluster": {:hex, :dns_cluster, "0.1.3", "0bc20a2c88ed6cc494f2964075c359f8c2d00e1bf25518a6a6c7fd277c9b0c66", [:mix], [], "hexpm", "46cb7c4a1b3e52c7ad4cbe33ca5079fbde4840dedeafca2baf77996c2da1bc33"},
+  "earmark": {:hex, :earmark, "1.4.47", "7e7596b84fe4ebeb8751e14cbaeaf4d7a0237708f2ce43630cfd9065551f94ca", [:mix], [], "hexpm", "3e96bebea2c2d95f3b346a7ff22285bc68a99fbabdad9b655aa9c6be06c698f8"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.43", "34b2f401fe473080e39ff2b90feb8ddfeef7639f8ee0bbf71bb41911831d77c5", [:mix], [], "hexpm", "970a3cd19503f5e8e527a190662be2cee5d98eed1ff72ed9b3d1a3d466692de8"},
   "ecto": {:hex, :ecto, "3.12.5", "4a312960ce612e17337e7cefcf9be45b95a3be6b36b6f94dfb3d8c361d631866", [:mix], [{:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "6eb18e80bef8bb57e17f5a7f068a1719fbda384d40fc37acb8eb8aeca493b6ea"},
   "eini": {:hex, :eini_beam, "2.2.4", "02143b1dce4dda4243248e7d9b3d8274b8d9f5a666445e3d868e2cce79e4ff22", [:rebar3], [], "hexpm", "12de479d144b19e09bb92ba202a7ea716739929afdf9dff01ad802e2b1508471"},