Improve import error messages

lib/livebook/live_markdown/import.ex

@@ -379,6 +379,9 @@ defmodule Livebook.LiveMarkdown.Import do
 
   defp grab_leading_comments(elems), do: {[], elems}
 
+  @unknown_hub_message "this notebook belongs to an Organization you don't have access to. " <>
+                         "Head to Livebook's home and add the Organization to your application before reopening this notebook"
+
   defp notebook_metadata_to_attrs(metadata) do
     Enum.reduce(metadata, {%{}, []}, fn
       {"persist_outputs", persist_outputs}, {attrs, messages} ->
@@ -395,7 +398,7 @@ defmodule Livebook.LiveMarkdown.Import do
       {"hub_id", hub_id}, {attrs, messages} ->
         cond do
           Hubs.hub_exists?(hub_id) -> {Map.put(attrs, :hub_id, hub_id), messages}
-          true -> {attrs, messages ++ ["ignoring notebook Hub with unknown id"]}
+          true -> {attrs, messages ++ [@unknown_hub_message]}
         end
 
       {"app_settings", app_settings_metadata}, {attrs, messages} ->
@@ -602,6 +605,10 @@ defmodule Livebook.LiveMarkdown.Import do
   defp take_stamp_data([{:stamp, data} | elements]), do: {data, elements}
   defp take_stamp_data(elements), do: {nil, elements}
 
+  @invalid_stamp_message "invalid notebook stamp, disabling default access to secrets and remote file systems "
+  @personal_stamp_context "(you are either not the author of this notebook or changed its source outside of Livebook)"
+  @org_stamp_context "(this may happen if you made changes to the notebook source outside of Livebook)"
+
   defp postprocess_stamp(notebook, _notebook_source, nil), do: {notebook, []}
 
   defp postprocess_stamp(notebook, notebook_source, stamp_data) do
@@ -614,7 +621,15 @@ defmodule Livebook.LiveMarkdown.Import do
         notebook = apply_stamp_metadata(notebook, metadata)
         {true, notebook, []}
       else
-        _ -> {false, notebook, ["failed to verify notebook stamp"]}
+        _ ->
+          extra =
+            if notebook.hub_id == "personal-hub" do
+              @personal_stamp_context
+            else
+              @org_stamp_context
+            end
+
+          {false, notebook, [@invalid_stamp_message <> extra]}
       end
 
     # We enable teams features for offline hub only if the stamp

test/livebook/live_markdown/import_test.exs

@@ -768,8 +768,8 @@ defmodule Livebook.LiveMarkdown.ImportTest do
 
     {notebook, messages} = Import.notebook_from_livemd(markdown)
 
-    assert messages == ["ignoring notebook Hub with unknown id"]
     assert notebook.hub_id != "nonexistent"
+    assert ["this notebook belongs to an Organization you don't have access to" <> _] = messages
   end
 
   describe "app settings" do
@@ -1141,7 +1141,7 @@ defmodule Livebook.LiveMarkdown.ImportTest do
       {notebook, messages} = Import.notebook_from_livemd(markdown)
 
       assert %Notebook{hub_secret_names: []} = notebook
-      assert messages == ["failed to verify notebook stamp"]
+      assert ["invalid notebook stamp" <> _] = messages
     end
 
     test "restores hub secret names from notebook stamp using offline hub" do
@@ -1186,7 +1186,7 @@ defmodule Livebook.LiveMarkdown.ImportTest do
       {notebook, messages} = Import.notebook_from_livemd(markdown)
 
       assert %Notebook{hub_id: "team-org-number-3079", teams_enabled: true} = notebook
-      assert messages == ["failed to verify notebook stamp"]
+      assert ["invalid notebook stamp" <> _] = messages
     end
 
     test "sets :teams_enabled to true when the teams hub exist regardless the stamp" do