From 5c32977db3af8fc7d05e036a3fac8176524473b6 Mon Sep 17 00:00:00 2001
From: "Maarten A. Breddels" <maartenbreddels@gmail.com>
Date: Wed, 19 Aug 2020 16:32:29 +0200
Subject: [PATCH] fix: stop executing cells when an error is encountered
 (replaces #530)

Co-authored-by: martinRenou <martin.renou@gmail.com>
---
 tests/app/syntax_error_test.py     | 4 +++-
 tests/notebooks/syntax_error.ipynb | 9 +++++++++
 voila/execute.py                   | 3 ---
 voila/handler.py                   | 9 ++++++++-
 4 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/tests/app/syntax_error_test.py b/tests/app/syntax_error_test.py
index e395f7a74..77da5a84b 100644
--- a/tests/app/syntax_error_test.py
+++ b/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
diff --git a/tests/notebooks/syntax_error.ipynb b/tests/notebooks/syntax_error.ipynb
index a26cb8a30..042971835 100644
--- a/tests/notebooks/syntax_error.ipynb
+++ b/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": {
diff --git a/voila/execute.py b/voila/execute.py
index c272c0603..773efb57c 100644
--- a/voila/execute.py
+++ b/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():
diff --git a/voila/handler.py b/voila/handler.py
index 16ebdbf3f..78609f0df 100644
--- a/voila/handler.py
+++ b/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()