bug #4909 Report regular expression errors from the matches operator (fabpot)

This PR was merged into the 3.x branch.

Discussion
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Report regular expression errors from the matches operator

The `matches` operator now throws a `RuntimeError` when PCRE cannot evaluate a regular expression instead of silently treating the error as a non-match.

This makes failures such as exhausted backtrack limits visible to template authors.

Commits
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e5347301d7 Throw on PCRE errors in the matches operator

CHANGELOG

@@ -1,5 +1,6 @@
 # 3.29.0 (2026-XX-XX)
 
+ * Fix the `matches` operator silently treating PCRE execution errors as non-matches
  * Add the `HtmlExtension::htmlAttrValue()` method to resolve a single HTML attribute value the way the `html_attr` function renders it
  * Fix `html_attr` JSON encoding a `Stringable` value in a `data-*` attribute instead of using its string representation
  * Add documentation comments to attach metadata to nodes (experimental)

src/Extension/CoreExtension.php

@@ -1188,7 +1188,7 @@ final class CoreExtension extends AbstractExtension
     }
 
     /**
-     * @throws RuntimeError When an invalid pattern is used
+     * @throws RuntimeError When the regular expression cannot be evaluated
      *
      * @internal
      */
@@ -1198,7 +1198,11 @@ final class CoreExtension extends AbstractExtension
             throw new RuntimeError(\sprintf('Regexp "%s" passed to "matches" is not valid', $regexp).substr($m, 12));
         });
         try {
-            return preg_match($regexp, $str ?? '');
+            if (false === $result = preg_match($regexp, $str ?? '')) {
+                throw new RuntimeError(\sprintf('Regexp "%s" passed to "matches" failed: %s.', $regexp, preg_last_error_msg()));
+            }
+
+            return $result;
         } finally {
             restore_error_handler();
         }

tests/Fixtures/expressions/matches_error_execution.test

@@ -0,0 +1,8 @@
+--TEST--
+Twig reports PCRE execution failures for the "matches" operator
+--TEMPLATE--
+{{ subject matches regexp }}
+--DATA--
+return ['subject' => 'aX', 'regexp' => '~(*LIMIT_MATCH=1)^(a+)+$~'];
+--EXCEPTION--
+Twig\Error\RuntimeError: Regexp "~(*LIMIT_MATCH=1)^(a+)+$~" passed to "matches" failed: Backtrack limit exhausted in "index.twig" at line 2.