TimeBasedRollingPolicy does not honor HALF_DAY periodicity for pattern %d{yyyy-MM-dd-a} — rolls over only at midnight instead of 00:00 and 12:00 #976

When using a TimeBasedRollingPolicy with a date pattern containing the AM/PM marker (a), such as:

<fileNamePattern>/var/log/app.log.%d{yyyy-MM-dd-a}</fileNamePattern>

Logback initializes with the message:

The date pattern is 'yyyy-MM-dd-a'.
Roll-over at midnight.

and performs daily rotation only (00:00), not twice per day (00:00 and 12:00) as expected.

Expected behavior

For a pattern including the AM/PM token (a), Logback should detect HALF_DAY periodicity and rotate logs at midnight and noon.

Actual behavior

Startup message says “Roll-over at midnight.”

Only one rollover per day occurs.

The enum constant HALF_DAY exists in RollingCalendar (printPeriodicity() even prints "Roll-over at midday and midnight."), but this value is never selected by the periodicity detector.

Technical cause

From source inspection:

RollingCalendar#printPeriodicity() supports HALF_DAY.

However, RollingCalendar#innerGetEndOfNextNthPeriod() and the periodicity detector never implement logic for HALF_DAY, so detection always falls back to TOP_OF_DAY.

As a result, DefaultTimeBasedFileNamingAndTriggeringPolicy always logs “Roll-over at midnight.”

This behavior is reproducible in Logback 1.4.x (tested with 1.4.14) and appears to match the old LOGBACK-1552 report (“yyyy-MM-dd-a not working as expected”).

Steps to Reproduce

Configure:

<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
  <file>app.log</file>
  <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
    <fileNamePattern>app.log.%d{yyyy-MM-dd-a}</fileNamePattern>
  </rollingPolicy>
</appender>

Run an app that logs periodically.

Observe startup message and verify only one rotation at 00:00.

Proposed fix

Add explicit HALF_DAY handling in:

RollingCalendar#innerGetEndOfNextNthPeriod()

RollingCalendar#getPeriodicityType(…) (so %d{…a} correctly maps to HALF_DAY)
to align detection with printPeriodicity()’s existing message and enable true twice-daily rotation.