languagetool-org/languagetool · error · RuntimeException

Could not find day of week for '" + dayStr + "'

Error message

Could not find day of week for '" + dayStr + "'

What it means

The Esperanto DateCheckFilter maps Esperanto weekday-name prefixes to Calendar constants. getDayOfWeek throws a RuntimeException when the given day string does not start with any known Esperanto (or transliterated) weekday prefix such as 'ven' or 'sab'.

Source

Thrown at languagetool-language-modules/eo/src/main/java/org/languagetool/rules/eo/DateCheckFilter.java:88

    if (day.equals("naua"))  n += 9;
    return n;
  }

  @SuppressWarnings("ControlFlowStatementWithoutBraces")
  @Override
  protected int getDayOfWeek(String dayStr) {
    String day = dayStr.toLowerCase();
    if (day.startsWith("dim")) return Calendar.SUNDAY;
    if (day.startsWith("lun")) return Calendar.MONDAY;
    if (day.startsWith("mar")) return Calendar.TUESDAY;
    if (day.startsWith("mer")) return Calendar.WEDNESDAY;
    if (day.startsWith("ĵaŭ")) return Calendar.THURSDAY;
    if (day.startsWith("jau")) return Calendar.THURSDAY;
    if (day.startsWith("jhau")) return Calendar.THURSDAY;
    if (day.startsWith("jxau")) return Calendar.THURSDAY;
    if (day.startsWith("ven")) return Calendar.FRIDAY;
    if (day.startsWith("sab")) return Calendar.SATURDAY;
    throw new RuntimeException("Could not find day of week for '" + dayStr + "'");
  }

  @SuppressWarnings("ControlFlowStatementWithoutBraces")
  @Override
  protected String getDayOfWeek(Calendar date) {
    String englishDay=date.getDisplayName(Calendar.DAY_OF_WEEK, Calendar.LONG, Locale.UK);
    if (englishDay.equals("Sunday"))    return "dimanĉo";
    if (englishDay.equals("Monday"))    return "lundo";
    if (englishDay.equals("Tuesday"))   return "mardo";
    if (englishDay.equals("Wednesday")) return "merkredo";
    if (englishDay.equals("Thursday"))  return "jaŭdo";
    if (englishDay.equals("Friday"))    return "vendredo";
    if (englishDay.equals("Saturday"))  return "sabato";
    return "";
  }

  @SuppressWarnings({"ControlFlowStatementWithoutBraces", "MagicNumber"})
  @Override

View on GitHub (pinned to 2e990059ce)

Solutions

1. Verify the rule pattern only captures actual Esperanto weekday names.
2. Check the day string for typos or unsupported transliterations (e.g. 'jhau'/'jxau' variants) and add a prefix case if a legitimate spelling is missing.
3. Validate input in the rule so non-weekday tokens never reach the filter.

Example fix

// before
callGetDayOfWeek("lundoj"); // not matched
// after
callGetDayOfWeek("lun"); // matches Calendar.MONDAY

List<String> prefixes = List.of("lun","mar","mer","ĵaŭ","jau","jhau","jxau","ven","sab");
String day = dayStr.toLowerCase();
if (prefixes.stream().noneMatch(day::startsWith)) throw new IllegalArgumentException("Not an Esperanto weekday: " + dayStr);

try {
  int dow = filter.getDayOfWeek(dayStr);
} catch (RuntimeException e) {
  if (e.getMessage().startsWith("Could not find day of week")) { /* skip or log invalid day token */ }
}

When it happens

Trigger: A date-check rule passes a 'weekDay' token whose normalized lowercase text does not match any Esperanto weekday prefix handled by the if-chain (e.g. a misspelled day or a non-Esperanto word).

Common situations: Rules matching a token that turns out not to be a weekday; typos in rule patterns; alternate spellings not covered by the prefix list; test calls with invalid day strings (as in testGetDayOfWeek).

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Could not find month '" + monthStr + "'
• Set only 'weekDay' and 'date' for " + YMDDateCheckFilter.cla
• Format error in file ${path}, line: ${line}
• No IssueType found for name '" + name + "'. Valid values: "
• The number of forms and postags has to be the same in disamb

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/e32b0a8b2bce16e6. Report an issue: GitHub.