Fix */7 day-of-week step value parsing bug

[Copilot]

Summary

Fixes issue where cron expressions with day-of-week step values ≥ 7 (like */7) would fail with a parsing error instead of generating the correct description.

Problem

The expression "0 * * * */7" was throwing an exception:

An error occured when generating the expression description. Check the cron expression syntax.

This happened because the code was trying to convert the step value "7" to a DayOfWeek enum value, but DayOfWeek only accepts values 0-6 (Sunday through Saturday).

Root Cause

In ExpressionDescriptor.cs, the GetSegmentDescription method was calling getSingleItemDescription(segments[1]) for step intervals like "*/7". The getSingleItemDescription function tries to convert day numbers to day names using:

return m_culture.DateTimeFormat.GetDayName(((DayOfWeek)Convert.ToInt32(exp)));

When exp is "7", this throws an exception since DayOfWeek enum only supports 0-6.

Solution

Modified the step interval processing in GetSegmentDescription to use the raw step value directly instead of trying to convert it through getSingleItemDescription:

// Before
description = string.Format(getIntervalDescriptionFormat(segments[1]), getSingleItemDescription(segments[1]));

// After  
description = string.Format(getIntervalDescriptionFormat(segments[1]), segments[1]);

Results

• ✅ "0 * * * */7" now produces: "Every hour, every 7 days of the week"
• ✅ Step values > 7 (like */8, */10) also work correctly
• ✅ Individual day values (0-6) still convert to day names properly
• ✅ Range step values (like 1-5/2) continue to work as expected
• ✅ All existing tests pass (1509 tests)

Testing

Added test case TestsEvery7DayOfTheWeek to prevent regression:

[Fact]
public void TestsEvery7DayOfTheWeek()
{
  // GitHub Issue #188: https://github.com/bradymholt/cron-expression-descriptor/issues/188
  Assert.Equal("Every hour, every 7 days of the week", GetDescription("0 * * * */7"));
}

Fixes #188.

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[bradymholt]

Looks good. Thanks.

[github-actions]

The changes in PR were just released in 2.44.0 🎉.