[Xzzz]

Summary

Makes flag_activity the only record of flag changes: they are no longer written to bugs_activity, and bug history, bugmail and the BugModal activity stream read them from flag_activity.

Part 2 of 1806896, whose part 1 (#2657) moved flag_state_activity to core as flag_activity and writes every flag change to both tables.

Changes

• Bugzilla::Bug and Bugzilla::Attachment no longer log flagtypes.name to bugs_activity, the user merge in editusers.cgi writes its flag changes to flag_activity.
• GetBugActivity and BugMail's _get_diffs build the flag rows from flag_activity (previous state taken from the same flag's prior row) and ignore the old flagtypes.name rows in bugs_activity.
• The BugModal activity stream finds a flag's last change by its flag_id in flag_activity instead of matching the flag type name.
• New scripts/flag_activity_backfill.pl: copies the flag changes in bugs_activity that are missing from flag_activity. Before part 1, only review, feedback, needinfo and data-review were recorded there. Backfilled rows have flag_id 0, as the flag can't be recovered reliably from bugs_activity, their history entries show the new state without the previous one. Runs in batches of 1000 bugs, one transaction each, and skips rows already present, so it can be re-run.
• New t/flag-activity-backfill.t

The old flagtypes.name rows stay in bugs_activity, nothing is deleted.

Deploy steps

Without the backfill, history before part 1 loses its changes to flag types other than review, feedback, needinfo and data-review. The script is safe while the current code still writes both tables, so it can run before the switch:

1. From the new image, before the rollout: perl scripts/flag_activity_backfill.pl --dry-run, check the counts (unknown flag type counts changes to flag types deleted or renamed since; those are skipped).
2. Same command without --dry-run.
3. Roll out.
4. Optional: run the script again; it should insert 0 rows.

If it can only run after the rollout, run steps 1-2 right after it; until then those older changes are missing from bug history.

Test plan

• Set a needinfo, a review on an attachment and an approval flag, then clear one: bug history, the activity stream and the bugmail show each change with its previous state, and bugs_activity gets no new flagtypes.name row
• On a bug with older approval flag changes only in bugs_activity: missing from history before the backfill, shown after it
• Merge two users with pending requests in editusers.cgi: the reassigned requests appear in bug history

References

• Bugzilla link: 2085398
• Part 2 of 1806896

[Xzzz]

Please note that the test_sanity critic failure is the $$ on master fixed by #2795. I'll re-run CI once it's merged, it should go green, unless I missed stg ;)