languagetool-org/languagetool · error

Could not find day of week for '<dayStr>'

Error message

Could not find day of week for '<dayStr>'

What it means

DateCheckFilter.getDayOfWeek() maps Russian weekday names and abbreviations (пн, вт, ср...) to java.util.Calendar constants. When the matched token in a date expression is not in its hardcoded prefix/equals list, it throws this RuntimeException. This means the filter saw a weekday token it does not recognize, typically due to an inflected or unusual form not covered by the rules.

Source

Thrown at languagetool-language-modules/ru/src/main/java/org/languagetool/rules/ru/DateCheckFilter.java:46

public class DateCheckFilter extends AbstractDateCheckFilter {

  @Override
  protected Calendar getCalendar() {
    return Calendar.getInstance(Locale.forLanguageTag("ru"));
  }

  @SuppressWarnings("ControlFlowStatementWithoutBraces")
  @Override
  protected int getDayOfWeek(String dayStr) {
    String day = dayStr.toLowerCase();
    if (day.startsWith("пн") || day.equals("понедельник")) return Calendar.MONDAY;
    if (day.startsWith("вт")) return Calendar.TUESDAY;
    if (day.startsWith("ср")) return Calendar.WEDNESDAY;
    if (day.startsWith("чт") || day.equals("четверг")) return Calendar.THURSDAY;
    if (day.equals("пт") || day.startsWith ("пятниц")) return Calendar.FRIDAY;
    if (day.startsWith("сб") || day.startsWith ("суббот")) return Calendar.SATURDAY;
    if (day.startsWith("вс") || day.equals("воскресенье")) return Calendar.SUNDAY;
    throw new RuntimeException("Could not find day of week for '" + dayStr + "'");
  }

  @Override
  protected String getDayOfWeek(Calendar date) {
    return date.getDisplayName(Calendar.DAY_OF_WEEK, Calendar.LONG, Locale.forLanguageTag("ru"));
  }

  @SuppressWarnings({"ControlFlowStatementWithoutBraces", "MagicNumber"})
  @Override
  protected int getMonth(String monthStr) {
    String mon = monthStr.toLowerCase();
    if (mon.equals("январь") || monthStr.equals("I") || mon.equals("января") || mon.equals("янв")) return 1;
    if (mon.equals("февраль") || monthStr.equals("II") ||  mon.equals("февраля") || mon.equals("фев")) return 2;
    if (mon.equals("март") || monthStr.equals("III") || mon.equals("марта") || mon.equals("мар")) return 3;
    if (mon.equals("апрель") || monthStr.equals("IV") || mon.equals("апреля") || mon.equals("апр")) return 4;
    if (mon.equals("май") || monthStr.equals("V") || mon.equals("мая")) return 5;
    if (mon.equals("июнь") || monthStr.equals("VI") || mon.equals("июня") || mon.equals("ин")) return 6;
    if (mon.equals("июль") || monthStr.equals("VII") || mon.equals("июля") || mon.equals("ил")) return 7;

View on GitHub (pinned to 2e990059ce)

Solutions

1. Add the failing token's prefix/equals case to the if-chain in DateCheckFilter.getDayOfWeek (languagetool-language-modules/ru/src/main/java/org/languagetool/rules/ru/DateCheckFilter.java:46) and return the matching Calendar constant
2. Find the actual token from the exception message and check which regex rule produced it, then constrain the rule so only known weekday forms reach the filter
3. Add a unit test in DateCheckFilterTest for the new token to prevent regressions
4. As a defensive measure, replace the throw with a logged fallback (return -1) if you maintain a fork, so unmatched tokens do not crash rule evaluation

Example fix

// before
if (day.startsWith("вт")) return Calendar.TUESDAY;
...
throw new RuntimeException("Could not find day of week for '" + dayStr + "'");
// after
if (day.startsWith("вт") || day.startsWith("вторник")) return Calendar.TUESDAY;
...
if (day.startsWith("пн") || day.startsWith("понедель")) return Calendar.MONDAY;
throw new RuntimeException("Could not find day of week for '" + dayStr + "'");

private static final Set<String> KNOWN_DAYS = Set.of("пн","вт","ср","чт","пт","сб","вс","понедель","вторник","сред","четверг","пятниц","суббот","воскресень");
boolean daySupported(String day) {
  return KNOWN_DAYS.stream().anyMatch(day::startsWith);
}
// call daySupported(token) before invoking the date filter

boolean isRecognizedRussianWeekday(String token) {
  String[] prefixes = {"пн","вт","ср","чт","пт","сб","вс","понедель","вторник","сред","четверг","пятниц","суббот","воскресень"};
  for (String p : prefixes) if (token.startsWith(p)) return true;
  return false;
}

try {
  result = filter.filter(readings, args);
} catch (RuntimeException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Could not find day of week")) {
    log.warn("Unrecognized weekday token skipped: {}", e.getMessage());
  } else { throw e; }
}

When it happens

Trigger: A Russian date rule matched text whose weekday field is an unrecognized form, e.g. a rare inflection like 'во вторник' handled incorrectly, an abbreviation not covered ('втор'), a misspelling, or a form added by a new regex rule that was not synced with getDayOfWeek's prefix list. Any call to DateCheckFilter with a day-of-week token failing all startsWith/equals checks reaches the throw.

Common situations: Adding/extending Russian date regex rules in the ru module without updating DateCheckFilter; users writing dates with inflected weekday forms ('понедельник' vs covered prefix); corpus/grammar tests containing date variants the hard-coded list omits; typos in test sentences.

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>'
• Could not find day of week for '<dayStr>'
• Could not find month '<monthStr>'
• Could not tag and disambiguate '<token>'
• Could not find day of week for '" + dayStr + "'

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/1c82dab27b35b94d. Report an issue: GitHub.