One of the earliest features I wrote for the Debian bug tracking system (Debbugs) after joining the team was support for forcibly merging bugs. Originally, merging two bugs required that the bugs be in exactly the same state before merging them; forcemerge removed this requirement.

Unfortunately, the way I originally implemented this was shortsighted, and merely forced the merge partners to have the same values as the merge master. This meant that owners, blocking bugs, and many other things were silently changed, which meant that people weren't notified of changes, and bugs could end up in an inconsistent state.

A while ago, I decided to fix this by calculating the changes required to actually merge the bugs, making those changes, and then merging the bugs normally; thus, doing everything that a maintainer would normally have done for them. This necessitated abstracting out the entire control apparatus into the Debbugs::Control module.

Now that it's complete, you can do the following:

> forcemerge 1 2
Bug #1 [foo] new title
Bug #2 {Done: foo@bugs.something} [foo] foo
Unset bug forwarded-to-address
Severity set to 'wishlist' from 'grave'
3 was blocked by: 2
3 was not blocking any bugs.
Removed blocking bug(s) of 3: 2
2 was blocked by: 4
2 was not blocking any bugs.
Removed blocking bug(s) of 2: 4
Bug reopened
Removed annotation that bug was owned by

Removed indication that 2 affects bleargh
Removed tag(s) unreproducible and moreinfo.
Merged 1 2
> thanks
Stopping processing here.

and bug 2 now is merged with 1 and matches the state of 1. [The above is the control output from the appropriate bit of the 06_mail_handling.t test.]

This change also means that I'll be able to finally write support for control@ operations at submit@ time. Also, all of the bug modifications that happen at submit@ or nnn@ time (setting title, found, etc.) will be implemented as calls to Debbugs::Control so we can eventually keep a postgresql database updated in addition to the flatfile database.