languagetool-org/languagetool · error · UnsupportedPatternRuleException

Elements with unified tokens are not supported.

Error message

Elements with unified tokens are not supported.

What it means

Search-index guard in checkUnsupportedElement: the pattern token uses unified (matching) tokens, whose cross-token agreement semantics cannot be expressed in a Lucene query.

Source

Thrown at languagetool-wikipedia/src/main/java/org/languagetool/dev/index/PatternRuleQueryBuilder.java:249

      if (str.contains("?iu") || str.contains("?-i")) {
        // Lucene's RegexpQuery doesn't seem to support this
        throw new UnsupportedPatternRuleException("Regex constructs like '?iu' and '?-i' are not supported: " + patternToken);
      }
      return new RegexpQuery(term);
    } catch (IllegalArgumentException e) {
      // constructs like "\p{Punct}" not supported by Lucene RegExp:
      throw new UnsupportedPatternRuleException("Advanced regex like '\\p{Punct}' are not supported: " + patternToken);
    }
  }

  private void checkUnsupportedElement(PatternToken patternPatternToken)
      throws UnsupportedPatternRuleException {
    if (patternPatternToken.hasOrGroup()) {
      // TODO: this is not enough: the first of the tokens in the <or> group will not get into this branch
      throw new UnsupportedPatternRuleException("<or> not yet supported.");
    }
    if (patternPatternToken.isUnified()) {
      throw new UnsupportedPatternRuleException("Elements with unified tokens are not supported.");
    }
    if (patternPatternToken.getString() != null && patternPatternToken.getString().matches("\\\\\\d+")) { // e.g. "\1"
      throw new UnsupportedPatternRuleException("Elements with only match references (e.g. \\1) are not supported.");
    }
  }

}

View on GitHub (pinned to 2e990059ce)

Solutions

1. Remove unification from the element for indexing purposes
2. Skip the rule during index-based checking
3. Post-filter matches with the full rule engine after a relaxed index query

When it happens

Trigger: Thrown at languagetool-wikipedia/src/main/java/org/languagetool/dev/index/PatternRuleQueryBuilder.java:249 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/8d05033072790f4e. Report an issue: GitHub.