fix: stop executing cells when an error is encountered (replaces voil…

…a-dashboards#530)

Co-authored-by: martinRenou <[email protected]>

tests/app/syntax_error_test.py

@@ -14,4 +14,6 @@ def voila_args(notebook_directory, voila_args_extra):
 async def test_syntax_error(capsys, http_server_client, syntax_error_notebook):
     response = await http_server_client.fetch(syntax_error_notebook)
     assert response.code == 200
-    assert 'There was an error when executing cell' in response.body.decode('utf-8')
+    output = response.body.decode('utf-8')
+    assert 'There was an error when executing cell' in output
+    assert 'This should not be executed' not in output

tests/notebooks/syntax_error.ipynb

@@ -8,6 +8,15 @@
    "source": [
     "this is a syntax error"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print('This should ' + 'not be executed')"
+   ]
   }
  ],
  "metadata": {

voila/execute.py

@@ -69,9 +69,6 @@ async def execute_cell(self, cell, resources, cell_index, store_history=True):
             self.log.error(e)
             self.show_code_cell_timeout(cell)
             raise e
-        except CellExecutionError as e:
-            self.log.error(e)
-            result = cell
 
         # Strip errors and traceback if not in debug mode
         if self.should_strip_error():

voila/handler.py

@@ -20,11 +20,12 @@
 import nbformat
 
 from nbconvert.preprocessors import ClearOutputPreprocessor
+from nbclient.exceptions import CellExecutionError
 from nbclient.util import ensure_async
 from tornado.httputil import split_host_and_port
 
 from ._version import __version__
-from .execute import VoilaExecutor
+from .execute import VoilaExecutor, strip_code_cell_warnings
 from .exporter import VoilaExporter
 
 
@@ -182,6 +183,12 @@ async def _jinja_cell_generator(self, nb, kernel_id):
             except TimeoutError:
                 output_cell = input_cell
                 break
+            except CellExecutionError as e:
+                if self.executor.should_strip_error():
+                    strip_code_cell_warnings(input_cell)
+                    self.executor.strip_code_cell_errors(input_cell)
+                output_cell = input_cell
+                break
             except Exception as e:
                 self.log.exception('Error at server while executing cell: %r', input_cell)
                 output_cell = nbformat.v4.new_code_cell()