bug#72830: Big rectangular selections are slow

["Mattias Engdegård" <mattias.engdegard@gmail.com>]

30 aug. 2024 kl. 17.20 skrev Mattias Engdegård <mattias.engdegard@gmail.com>:

> I think the patch is good enough for master.

And it has now been pushed. To recap, remaining concerns:

- `select-active-regions`: as mentioned, it slows down rectangle selection massively and is alien to non-X11 platforms so I'd suggest it be set to nil by default on macOS and Windows at least. Not sure what to do on TTY frames.
For that matter, on X11 it seems strange to copy the entire selection each time it is made or modified even slightly; PRIMARY selection data isn't sent to the server until actually requested.

- Rectangle operations other than selection are still very slow. This isn't quite as big a problem but still annoying. Both `move-to-column` and `line-end-position` are unexpectedly expensive here. (And shouldn't rect.el use `pos-eol` instead? It's not much faster, though.)

- There are some mostly theoretical cases when the current rectangular selection code produces ugly results. I don't think they are likely to occur in practice but would be happy to work with someone who thinks he or she can do better.