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 for Italian validates that a day-of-week found in text matches a recognized Italian weekday name or abbreviation. getDayOfWeek throws this RuntimeException when the extracted day string matches none of the known prefixes (lu, ma, me, gi, ve, sa) or full names. The filter assumes the regex that feeds it only matches valid weekdays, so an unmatched string indicates the rule regex and the filter are out of sync.

Source

Thrown at languagetool-language-modules/it/src/main/java/org/languagetool/rules/it/DateCheckFilter.java:48

public class DateCheckFilter extends AbstractDateCheckFilter {

  @Override
  protected Calendar getCalendar() {
    return Calendar.getInstance(Locale.UK);
  }

  @SuppressWarnings("ControlFlowStatementWithoutBraces")
  @Override
  protected int getDayOfWeek(String dayStr) {
    String day = dayStr.toLowerCase();
    if (day.startsWith("do") || day.equals("domenica")) return Calendar.SUNDAY;
    if (day.startsWith("lu") || day.equals("lunedì")) return Calendar.MONDAY;
    if (day.startsWith("ma") || day.equals("martedì")) return Calendar.TUESDAY;
    if (day.startsWith("me") || day.equals("mercoledì")) return Calendar.WEDNESDAY;
    if (day.startsWith("gi") || day.equals("giovedì")) return Calendar.THURSDAY;
    if (day.startsWith("ve") || day.equals("venerdì")) return Calendar.FRIDAY;
    if (day.startsWith("sa") || day.equals("sabato")) 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 "domenica";
    if (englishDay.equals("Monday")) return "lunedì";
    if (englishDay.equals("Tuesday")) return "martedì";
    if (englishDay.equals("Wednesday")) return "mercoledì";
    if (englishDay.equals("Thursday")) return "giovedì";
    if (englishDay.equals("Friday")) return "venerdì";
    if (englishDay.equals("Saturday")) return "sabato";
    return "";
  }

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

View on GitHub (pinned to 2e990059ce)

Solutions

1. Add the missing day mapping (notably Sunday: if (day.startsWith("do") || day.equals("domenica")) return Calendar.SUNDAY;) to getDayOfWeek
2. Check the exception message for the exact day string and verify how the calling rule's regex captured it (case, accents, partial word)
3. Ensure the rule regex only matches tokens covered by the mapping, or make matching case-insensitive/accent-aware before lookup

Example fix

// before
if (day.startsWith("sa") || day.equals("sabato")) return Calendar.SATURDAY;
throw new RuntimeException("Could not find day of week for '" + dayStr + "'");
// after
if (day.startsWith("sa") || day.equals("sabato")) return Calendar.SATURDAY;
if (day.startsWith("do") || day.equals("domenica")) return Calendar.SUNDAY;
throw new RuntimeException("Could not find day of week for '" + dayStr + "'");

Set<String> known = Set.of("lu","ma","me","gi","ve","sa","lunedì","martedì","mercoledì","giovedì","venerdì","sabato");
String d = dayStr.toLowerCase();
if (!known.stream().anyMatch(d::startsWith)) throw new IllegalArgumentException("Unrecognized Italian weekday: " + dayStr);

boolean isItalianWeekday(String s) { String d = s == null ? "" : s.toLowerCase(); return d.startsWith("lu")||d.startsWith("ma")||d.startsWith("me")||d.startsWith("gi")||d.startsWith("ve")||d.startsWith("sa"); }

try { cal.set(Calendar.DAY_OF_WEEK, filter.getDayOfWeek(dayStr)); } catch (RuntimeException e) { log.warn("Unknown weekday token: {}", dayStr); /* skip rule match */ }

When it happens

Trigger: A grammar rule matches a token as a weekday and passes it to getDayOfWeek, but the token is not one of lunedì/lu, martedì/ma, mercoledì/me, giovedì/gi, venerdì/ve, sabato/sa (e.g. 'dom' or 'domenica', which has no mapping — Sunday is missing from the chain).

Common situations: Text contains 'domenica' (Sunday) matched by the date rule but the mapping has no Sunday branch; adding new Italian weekday spellings or abbreviations to the rule regex without updating getDayOfWeek; case/accents normalized differently than expected.

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 find day of week for '<dayStr>'
• Could not find month '<monthStr>'

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/bc15666801e90d3b. Report an issue: GitHub.