Fix the handling of escaping in table cells (#391)

Using `str_replace` to perform the un-escaping is flawed because it
performs each of its search in order, which was not handling properly
the case of escaped backslashes.

Replacing escape sequences requires handling each backslash a single
time, to avoid considering the output of an escaped backslash as belong
to another escape sequence (or considering a backslash as being the
start of an escape sequence instead of being escape, depending on the
order). The solution for that is to use `preg_replace` matching a
backslash and its following character, thanks to the fact that this
function guarantees that it does not have overlapping matches for the
regex.

I extracted that parsing to a private method for 2 reasons:
1. we need an assertion to assume that the returned value is not `null`
(here, I'm assuming that the regex does not fail. I could turn that in
an exception if you prefer, but we already do the same assumption for
the splitting of cells)
2. a oneliner (which would use `??` to handle the null values) would
make that line quite hard to read

Author: stof

src/Lexer.php

@@ -753,7 +753,7 @@ protected function scanTableRow()
 
         $token = $this->takeToken('TableRow');
         if ($this->compatibilityMode->shouldSupportNewlineEscapeSequenceInTableCell()) {
-            $columns = array_map(static fn ($column) => trim(str_replace(['\\|', '\n', '\\\\'], ['|', "\n", '\\'], $column), ' '), $rawColumns);
+            $columns = array_map($this->parseTableCell(...), $rawColumns);
         } else {
             $columns = array_map(static fn ($column) => trim(str_replace(['\\|', '\\\\'], ['|', '\\'], $column)), $rawColumns);
         }
@@ -764,6 +764,22 @@ protected function scanTableRow()
         return $token;
     }
 
+    private function parseTableCell(string $cell): string
+    {
+        $value = preg_replace_callback('/\\\\./', function (array $matches) {
+            return match ($matches[0]) {
+                '\\n' => "\n",
+                '\\\\' => '\\',
+                '\\|' => '|',
+                default => $matches[0],
+            };
+        }, $cell);
+
+        assert($value !== null);
+
+        return trim($value, ' ');
+    }
+
     /**
      * Scans Tags from input & returns it if found.
      *

tests/Cucumber/CompatibilityTest.php

@@ -59,7 +59,6 @@ class CompatibilityTest extends TestCase
         'gherkin-32' => [
             'complex_background.feature' => 'Rule keyword not supported',
             'docstrings.feature' => 'Escaped delimiters in docstrings are not unescaped',
-            'escaped_pipes.feature' => 'Escaped newlines in table cells are not unescaped',
             'rule.feature' => 'Rule keyword not supported',
             'rule_with_tag.feature' => 'Rule keyword not supported',
             'tags.feature' => 'Rule keyword not supported',