Support multiple escaped pipes in table cells

e.g.

foo|bar
---|---
`\|\|`| The logical-or operator

src/render/MarkdownRenderer.php

@@ -13,7 +13,7 @@
 use type Facebook\Markdown\Blocks\TableExtensionColumnAlignment;
 use namespace HH\Lib\{C, Math, Str, Vec};
 
-/** Re-create Markdwon from the AST */
+/** Re-create Markdown from the AST */
 class MarkdownRenderer extends Renderer<string> {
   private ?string $outContext = null;
 

src/unparsed-blocks/TableExtension.php

@@ -146,7 +146,8 @@ private static function consumeRow(
         $parts[] = Str\slice($first, $start);
         break;
       }
-      if ($end >> 1 && $first[$end - 1] === '\\') {
+
+      while ($end !== null && $end > 1 && $first[(int) $end - 1] === '\\') {
         $end = Str\search($first, '|', $end + 1);
       }
 

tests/EdgeCaseTest.php

@@ -19,6 +19,14 @@ public function getManualExamples(
     return [
       tuple("- foo\n\n", "<ul>\n<li>foo</li>\n</ul>\n"),
       tuple("- foo\n\n\n", "<ul>\n<li>foo</li>\n</ul>\n"),
+      tuple(
+        "foo|bar\n---|---\n`\|\|`|herp\n",
+        "<table>\n<thead>\n".
+        "<tr>\n<th>foo</th>\n<th>bar</th>\n</tr>\n".
+        "</thead>\n<tbody>\n".
+        "<tr>\n<td><code>||</code></td>\n<td>herp</td>\n</tr>".
+        "</tbody></table>\n"
+      ),
       // Already covered in the spec, but emphasizing here as they
       // illustrate correct binding for the next problme
       tuple('**foo*', "<p>*<em>foo</em></p>\n"),
@@ -59,7 +67,7 @@ public function testManualExample(
       'unnamed',
       $in,
       $expected_html,
-      null,
+      /* extension = */ 'table',
     );
   }