languagetool-org/languagetool · error · RuntimeException

Error trying to synthesize POS tag " + posTag + " (posTagReg

Error message

Error trying to synthesize POS tag " + posTag + " (posTagRegExp: true) from token " + token.getToken()

What it means

Wrapper exception in BaseSynthesizer.synthesize for the posTagRegExp=true code path: treating the POS tag as a regular expression and synthesizing matching word forms failed unexpectedly, and the error is rethrown with the offending tag and token attached. The inputs at fault are the POS-tag pattern and the analyzed token passed by the calling rule.

Source

Thrown at languagetool-core/src/main/java/org/languagetool/synthesis/BaseSynthesizer.java:261

    }
    if (posTag.equals(SPELLNUMBER_FEMININE_TAG)) {
      return new String[] {getSpelledNumber("feminine " + token.getToken())};
    }
    if (posTag.equals(SPELLNUMBER_ROMAN_TAG)) {
      return new String[] {getRomanNumber(token.getToken())};
    }
    List<String> wordForms = lookup(token.getLemma(), posTag);
    return removeExceptions(wordForms.toArray(new String[0]));
  }

  @Override
  public String[] synthesize(AnalyzedToken token, String posTag, boolean posTagRegExp) throws IOException {
    if (posTagRegExp) {
      try {
        Pattern p = Pattern.compile(posTag);
        return synthesizeForPosTags(token.getLemma(), tag -> p.matcher(tag).matches());
      } catch (PatternSyntaxException e) {
        throw new RuntimeException("Error trying to synthesize POS tag " + posTag +
                " (posTagRegExp: true) from token " + token.getToken(), e);
      }
    }
    return removeExceptions(synthesize(token, posTag));
  }

  /**
   * Synthesize forms for the given lemma and for all POS tags satisfying the given predicate.
   * @since 5.3
   */
  public String[] synthesizeForPosTags(String lemma, Predicate<String> acceptTag) throws IOException {
    initPossibleTags();
    List<String> results = new ArrayList<>();
    for (String tag : possibleTags) {
      if (acceptTag.test(tag)) {
        results.addAll(lookup(lemma, tag));
      }
    }

View on GitHub (pinned to 2e990059ce)

Solutions

1. Inspect the chained cause to find the underlying failure (often an invalid regex in the POS tag)
2. Simplify the POS-tag regular expression to isolate the failing construct
3. Test the tag pattern against the synthesizer's list of possible tags to confirm it matches something

When it happens

Trigger: Thrown at languagetool-core/src/main/java/org/languagetool/synthesis/BaseSynthesizer.java:261 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/c5da20e32028f69c. Report an issue: GitHub.