Ref T7447. This ports comments forward and backward in the best case:
- The old comment is on a changeset with the same filename.
- The old and new files are pretty much the same, line-for-line.
This will fail to port a lot of comments around and probably port a lot of comments into goofy places. We can see how bad it is in practice.
Errata:
- Design is me cobbling something together, probably worth tweaking.
- "Old Comment" should, at a minimum, say "Newer Comment" sometimes, or we should come up with some better name for this stuff.