Include errors in exported notebook outputs (#3009)

lib/livebook/live_markdown/export.ex

@@ -238,12 +238,11 @@ defmodule Livebook.LiveMarkdown.Export do
   end
 
   defp render_output(%{type: :terminal_text, text: text}, _ctx) do
-    text = String.replace_suffix(text, "\n", "")
-    delimiter = MarkdownHelpers.code_block_delimiter(text)
-    text = strip_ansi(text)
+    render_text_output(text)
+  end
 
-    [delimiter, "\n", text, "\n", delimiter]
-    |> prepend_metadata(%{output: true})
+  defp render_output(%{type: :error, message: message}, _ctx) do
+    render_text_output(message)
   end
 
   defp render_output(%{type: :js, js_view: %{ref: ref}}, ctx) do
@@ -279,6 +278,14 @@ defmodule Livebook.LiveMarkdown.Export do
 
   defp render_output(_output, _ctx), do: :ignored
 
+  defp render_text_output(text) do
+    text = text |> strip_ansi() |> String.replace_suffix("\n", "")
+    delimiter = MarkdownHelpers.code_block_delimiter(text)
+
+    [delimiter, "\n", text, "\n", delimiter]
+    |> prepend_metadata(%{output: true})
+  end
+
   defp encode_js_data(data) when is_binary(data), do: {:ok, data}
 
   defp encode_js_data(data) do
@@ -349,7 +356,7 @@ defmodule Livebook.LiveMarkdown.Export do
     string
     |> Livebook.Utils.ANSI.parse_ansi_string()
     |> elem(0)
-    |> Enum.map(fn {_modifiers, string} -> string end)
+    |> Enum.map_join(fn {_modifiers, string} -> string end)
   end
 
   defp render_notebook_footer(_notebook, _notebook_source, _include_stamp? = false), do: {[], []}

test/livebook/live_markdown/export_test.exs

@@ -947,6 +947,57 @@ defmodule Livebook.LiveMarkdown.ExportTest do
     assert expected_document == document
   end
 
+  test "includes error outputs" do
+    notebook = %{
+      Notebook.new()
+      | name: "My Notebook",
+        sections: [
+          %{
+            Notebook.Section.new()
+            | name: "Section 1",
+              cells: [
+                %{
+                  Notebook.Cell.new(:code)
+                  | source: """
+                    raise "hello"\
+                    """,
+                    outputs: [
+                      {0,
+                       %{
+                         type: :error,
+                         message:
+                           "\e[31m** (RuntimeError) hello\e[0m\n\e[31m    #cell:tlbdimkdsfldvwge:1: (file)\n\e[0m",
+                         context: nil
+                       }}
+                    ]
+                }
+              ]
+          }
+        ]
+    }
+
+    expected_document = """
+    # My Notebook
+
+    ## Section 1
+
+    ```elixir
+    raise "hello"
+    ```
+
+    <!-- livebook:{"output":true} -->
+
+    ```
+    ** (RuntimeError) hello
+        #cell:tlbdimkdsfldvwge:1: (file)
+    ```
+    """
+
+    {document, []} = Export.notebook_to_livemd(notebook, include_outputs: true)
+
+    assert expected_document == document
+  end
+
   test "includes outputs when notebook has :persist_outputs set" do
     notebook = %{
       Notebook.new()