Fix output ambiguity in livemd import/export (#892)

* Fix output ambiguity in livemd import/export

* Update test/livebook/live_markdown/import_test.exs

Co-authored-by: José Valim <jose.valim@dashbit.co>

Co-authored-by: José Valim <jose.valim@dashbit.co>

lib/livebook/live_markdown.ex

@@ -36,6 +36,8 @@ defmodule Livebook.LiveMarkdown do
   #        - `{"break_markdown":true}` - an annotation splitting the markdown content
   #          into separate Markdown cells
   #
+  #        - `{"output":true}` - an annotation marking a code snippet as cell output
+  #
   #        - section metadata, recognised keys `branch_parent_index`
   #
   #        - cell metadata, recognised keys: `disable_formatting`

lib/livebook/live_markdown/export.ex

@@ -161,13 +161,17 @@ defmodule Livebook.LiveMarkdown.Export do
     text = String.replace_suffix(text, "\n", "")
     delimiter = MarkdownHelpers.code_block_delimiter(text)
     text = strip_ansi(text)
-    [delimiter, "output\n", text, "\n", delimiter]
+
+    [delimiter, "\n", text, "\n", delimiter]
+    |> prepend_metadata(%{output: true})
   end
 
   defp render_output({:text, text}, _ctx) do
     delimiter = MarkdownHelpers.code_block_delimiter(text)
     text = strip_ansi(text)
-    [delimiter, "output\n", text, "\n", delimiter]
+
+    [delimiter, "\n", text, "\n", delimiter]
+    |> prepend_metadata(%{output: true})
   end
 
   defp render_output(
@@ -180,7 +184,10 @@ defmodule Livebook.LiveMarkdown.Export do
 
     case encode_js_data(payload) do
       {:ok, binary} ->
-        ["```", info_string, "\n", binary, "\n", "```"]
+        delimiter = MarkdownHelpers.code_block_delimiter(binary)
+
+        [delimiter, info_string, "\n", binary, "\n", delimiter]
+        |> prepend_metadata(%{output: true})
 
       _ ->
         :ignored

lib/livebook/live_markdown/import.ex

@@ -180,6 +180,7 @@ defmodule Livebook.LiveMarkdown.Import do
     end
   end
 
+  # Import ```output snippets for backward compatibility
   defp take_outputs(
          [{"pre", _, [{"code", [{"class", "output"}], [output], %{}}], %{}} | ast],
          outputs
@@ -187,6 +188,29 @@ defmodule Livebook.LiveMarkdown.Import do
     take_outputs(ast, [{:text, output} | outputs])
   end
 
+  defp take_outputs(
+         [
+           {:comment, _, [~s/livebook:{"output":true}/], %{comment: true}},
+           {"pre", _, [{"code", [], [output], %{}}], %{}}
+           | ast
+         ],
+         outputs
+       ) do
+    take_outputs(ast, [{:text, output} | outputs])
+  end
+
+  # Ignore other exported outputs
+  defp take_outputs(
+         [
+           {:comment, _, [~s/livebook:{"output":true}/], %{comment: true}},
+           {"pre", _, [{"code", [{"class", _info_string}], [_output], %{}}], %{}}
+           | ast
+         ],
+         outputs
+       ) do
+    take_outputs(ast, outputs)
+  end
+
   defp take_outputs(ast, outputs), do: {outputs, ast}
 
   # Builds a notebook from the list of elements obtained in the previous step.

test/livebook/live_markdown/export_test.exs

@@ -584,7 +584,9 @@ defmodule Livebook.LiveMarkdown.ExportTest do
       IO.puts("hey")
       ```
 
-      ```output
+      <!-- livebook:{"output":true} -->
+
+      ```
       hey
       ```
       """
@@ -624,11 +626,15 @@ defmodule Livebook.LiveMarkdown.ExportTest do
       IO.puts("hey")
       ```
 
-      ```output
+      <!-- livebook:{"output":true} -->
+
+      ```
       hey
       ```
 
-      ```output
+      <!-- livebook:{"output":true} -->
+
+      ```
       :ok
       ```
       """
@@ -754,6 +760,8 @@ defmodule Livebook.LiveMarkdown.ExportTest do
       :ok
       ```
 
+      <!-- livebook:{"output":true} -->
+
       ```mermaid
       graph TD;
       A-->B;
@@ -802,6 +810,8 @@ defmodule Livebook.LiveMarkdown.ExportTest do
       :ok
       ```
 
+      <!-- livebook:{"output":true} -->
+
       ```box
       {"height":50,"width":50}
       ```
@@ -853,6 +863,8 @@ defmodule Livebook.LiveMarkdown.ExportTest do
       :ok
       ```
 
+      <!-- livebook:{"output":true} -->
+
       ```vega-lite
       {"height":50,"width":50}
       ```
@@ -897,7 +909,9 @@ defmodule Livebook.LiveMarkdown.ExportTest do
     IO.puts("hey")
     ```
 
-    ```output
+    <!-- livebook:{"output":true} -->
+
+    ```
     hey
     ```
     """

test/livebook/live_markdown/import_test.exs

@@ -340,6 +340,8 @@ defmodule Livebook.LiveMarkdown.ImportTest do
     Enum.to_list(1..10)
     ```
 
+    <!-- livebook:{"force_markdown":true} -->
+
     ```erlang
     spawn_link(fun() -> io:format("Hiya") end).
     ```
@@ -566,11 +568,15 @@ defmodule Livebook.LiveMarkdown.ImportTest do
       IO.puts("hey")
       ```
 
-      ```output
+      <!-- livebook:{"output":true} -->
+
+      ```
       hey
       ```
 
-      ```output
+      <!-- livebook:{"output":true} -->
+
+      ```
       :ok
       ```
       """
@@ -596,6 +602,63 @@ defmodule Livebook.LiveMarkdown.ImportTest do
              } = notebook
     end
 
+    test "discards other output snippets" do
+      markdown = """
+      # My Notebook
+
+      ## Section 1
+
+      ```elixir
+      IO.puts("hey")
+      ```
+
+      ```elixir
+      plot()
+      ```
+
+      <!-- livebook:{"output":true} -->
+
+      ```vega-lite
+      {}
+      ```
+
+      ```elixir
+      :ok
+      ```
+      """
+
+      {notebook, []} = Import.notebook_from_markdown(markdown)
+
+      assert %Notebook{
+               name: "My Notebook",
+               sections: [
+                 %Notebook.Section{
+                   name: "Section 1",
+                   cells: [
+                     %Cell.Elixir{
+                       source: """
+                       IO.puts("hey")\
+                       """,
+                       outputs: []
+                     },
+                     %Cell.Elixir{
+                       source: """
+                       plot()\
+                       """,
+                       outputs: []
+                     },
+                     %Cell.Elixir{
+                       source: """
+                       :ok\
+                       """,
+                       outputs: []
+                     }
+                   ]
+                 }
+               ]
+             } = notebook
+    end
+
     test "imports notebook :persist_outputs attribute" do
       markdown = """
       <!-- livebook:{"persist_outputs":true} -->
@@ -654,5 +717,49 @@ defmodule Livebook.LiveMarkdown.ImportTest do
                  " Also, to make the input reactive you can use an automatically reevaluating cell"
              ] == messages
     end
+
+    test "imports snippets with output info string" do
+      # We now explicitly mark every output sinppet with <!-- livebook:{"output":true} -->
+      # and use empty snippets for textual outputs, however previously
+      # we supported ```output too, so let's ensure they still work
+
+      markdown = """
+      # My Notebook
+
+      ## Section 1
+
+      ```elixir
+      IO.puts("hey")
+      ```
+
+      ```output
+      hey
+      ```
+
+      ```output
+      :ok
+      ```
+      """
+
+      {notebook, []} = Import.notebook_from_markdown(markdown)
+
+      assert %Notebook{
+               name: "My Notebook",
+               sections: [
+                 %Notebook.Section{
+                   name: "Section 1",
+                   cells: [
+                     %Cell.Elixir{
+                       source: """
+                       IO.puts("hey")\
+                       """,
+                       outputs: [{0, {:text, ":ok"}}, {1, {:text, "hey"}}]
+                     }
+                   ]
+                 }
+               ],
+               output_counter: 2
+             } = notebook
+    end
   end
 end

test/livebook_web/controllers/session_controller_test.exs

@@ -114,7 +114,9 @@ defmodule LivebookWeb.SessionControllerTest do
              IO.puts("hey")
              ```
 
-             ```output
+             <!-- livebook:{"output":true} -->
+
+             ```
              hey
              ```
              """