can_purge_log() reports "it is the current active binlog" for a log that is not active

can_purge_log() reports it is the current active binlog for a binary log that is not the active one. In the reproduction below the refusal names ...-bin.000003 while ...-bin.000008 is active.

Where

Two unrelated conditions share one reason string (sql/log.cc):

  if (is_active(log_file_name_arg) ||

      (!is_relay_log && waiting_for_slave_to_change_binlog &&

       purge_sending_new_binlog_file == sending_new_binlog_file &&

       !strcmp(log_file_name_arg, purge_binlog_name)))

  {

    reason= "it is the current active binlog";

    goto error;

  }

The first condition is what the string says. The second – "this file was refused a moment ago and nothing has changed since" – says nothing about the file being active, and in general it is not.

The refusal that populated the cache had already reported the real reason, either "less than 'slave_connections_needed_for_purge' slaves have processed it" or "it is in use by a slave thread", so the information needed is available at the point the cache is written. Carrying the recorded reason alongside purge_binlog_name, or simply wording the cached branch for what it means, would fix it independently of the behavioral bug in MDEV-41214.

Why it has stayed hidden

On the non-interactive path, purge_warning_given suppresses the note on every refusal after the first until a purge succeeds, so an automatic purge usually does not print it twice. An interactive caller is exempt from that suppression, so a human running PURGE BINARY LOGS is the one most likely to be told something false.

Steps to reproduce

As in MDEV-41214, whose attached mtr test manifests this too: on a standalone master with no slaves and default settings, let one automatic purge be refused, then run PURGE BINARY LOGS TO against a later file.

Expected

The reason given is the reason the purge was actually refused.

Actual

Note 1375  Binary log '...-bin.000003' is not purged because it is the

           current active binlog

Relationship to MDEV-41214

Separable, and deliberately filed on its own: fixing the interactive inheritance in MDEV-41214 still leaves this branch reporting the wrong reason for a genuine and correct refusal of an automatic purge.

Versions

Introduced by 18dfcfdecf4 (MDEV-31404), first released in 11.4.1. Reproduced on 13.0.2-MariaDB-log.

Priority deliberately left at the project default: severity is not mine to rate.