parse error message in case of assignment to literal

nbqa/output_parser.py

@@ -38,7 +38,9 @@ def _get_pattern(
             (
                 rf"(?<=^error: cannot format {re.escape(str(notebook))}: Cannot parse: )\d+",
                 standard_substitution,
-            )
+            ),
+            (r"(?<=line )\d+(?=\)\nOh no! )", standard_substitution),
+            (r"line cell_(?=\d+:\d+\)\nOh no! )", "cell_"),
         ]
 
     if command == "doctest":

tests/invalid_data/assignment_to_literal.ipynb

@@ -0,0 +1,35 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "1 = [1,2,3]"
+   ]
+  }
+ ],
+ "metadata": {
+  "anaconda-cloud": {},
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.0-final"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}

tests/tools/test_black.py

@@ -19,6 +19,8 @@
 
 SPARKLES = "\N{sparkles}"
 SHORTCAKE = "\N{shortcake}"
+COLLISION = "\N{collision symbol}"
+BROKEN_HEART = "\N{broken heart}"
 
 
 def test_black_works(tmp_notebook_for_testing: Path, capsys: "CaptureFixture") -> None:
@@ -343,3 +345,39 @@ def test_black_works_with_leading_comment(capsys: "CaptureFixture") -> None:
     expected_err = ""
     assert expected_out == out
     assert expected_err == err
+
+
+def test_black_works_with_literal_assignment(capsys: "CaptureFixture") -> None:
+    """
+    Check black works with notebooks with invalid syntax (e.g. assignment to literal).
+
+    Parameters
+    ----------
+    capsys
+        Pytest fixture to capture stdout and stderr.
+    """
+    path = os.path.abspath(
+        os.path.join("tests", "invalid_data", "assignment_to_literal.ipynb")
+    )
+
+    with pytest.raises(SystemExit):
+        main(["black", path])
+
+    out, err = capsys.readouterr()
+    expected_out = ""
+    expected_err = (
+        (
+            f"error: cannot format {path}: "
+            "cannot use --safe with this file; failed to parse source file.  AST error message: "
+            "can't assign to literal (<unknown>, cell_1:1)\nOh no! "
+            f"{COLLISION} {BROKEN_HEART} {COLLISION}\n1 file failed to reformat.\n"
+        )
+        .encode("ascii", "backslashreplace")
+        .decode()
+    )
+    # This is required because linux supports emojis
+    # so both should have \\ for comparison
+    err = err.encode("ascii", "backslashreplace").decode()
+
+    assert expected_out == out
+    assert expected_err == err