python: provide informative exception for trailing escapes in tables (#…

…241)

With the Python implementation:

1. Whitespace either side of a table row is stripped.
2. The table row is passed to a function to strip and yields its cell
   values
3. Characters in each cell are iterated over to handle them
   appropriately, such as new columns (|), escape characters, etc.
4. As escape characters are typically followed by a special character
   (e.g. n, t), when an escape character is detected \\ an additional
   next call is made to grab the next character
5. As in step 1, whitespace after a trailing escape character (\\)
   would be stripped, there would not be a following character and a
   StopIteration error is raised.

CHANGELOG.md

@@ -8,8 +8,9 @@ This document is formatted according to the principles of [Keep A CHANGELOG](htt
 
 ## [Unreleased]
 ### Fixed
-- Provide trailing space in Irish keywords ([#243](https://github.com/cucumber/gherkin/pull/243))
-- Tamil "And" and "But" translations should have single trailing space ([#243](https://github.com/cucumber/gherkin/pull/243))
+- [Python] Provide informative exception for trailing escapes in tables ([#241](https://github.com/cucumber/gherkin/pull/241))
+- (i18n) Provide trailing space in Irish keywords ([#243](https://github.com/cucumber/gherkin/pull/243))
+- (i18n) Tamil "And" and "But" translations should have single trailing space ([#243](https://github.com/cucumber/gherkin/pull/243))
 
 ## [28.0.0] - 2024-02-15
 ### Added

python/gherkin/gherkin_line.py

@@ -59,7 +59,7 @@ def split_table_cells(self, row):
                 cell = ''
                 start_col = col + 1
             elif char == '\\':
-                char = next(row)
+                char = next(row, "")
                 col += 1
                 if char == 'n':
                     cell += '\n'

python/test/gherkin_test.py

@@ -2,7 +2,7 @@
 from gherkin.token_scanner import TokenScanner
 from gherkin.token_matcher import TokenMatcher
 from gherkin.parser import Parser
-from gherkin.errors import ParserError
+from gherkin.errors import CompositeParserException, ParserError
 import pytest
 
 
@@ -89,3 +89,18 @@ def test_change_the_default_language():
     }
 
     assert expected == feature_file
+
+@pytest.mark.parametrize("trailing_text", ["\\", "\\ "])
+def test_inconsistent_cell_count_with_trailing_escape(trailing_text):
+    feature_text = """Feature:
+    Scenario:
+      Given I have a table
+        | Name | Value |
+        | A    | """ + trailing_text
+    parser = Parser()
+
+    with pytest.raises(
+        CompositeParserException,
+        match="inconsistent cell count within the table",
+    ):
+        parser.parse(TokenScanner(feature_text))