Should `Mouse` mode be detected as supported on `foot`?

[Rosuavio]

I noticed that Mouse mode was not detected as supported on my terminal emulator, foot term. I believe it is the terminal that sway's default configs use.

I noticed that the code enables Mouse mode for specific terminal name prefixes, terminals that are deemed "Xterm like". Not sure if foot is "Xterm like" or what that means, but from my limited understanding and experiments the mouse escape codes seem to work on foot. I ran the php script from this https://stackoverflow.com/a/58390575 post and it seemed to detect all my mouse events.

[jtdaugherty]

Hi @Rosuavio - here's a bit of context:

vty-unix doesn't enable mouse mode by default for any terminals, but the XTermColor backend does support mouse mode in that it honors requests to enable mouse mode and accept mouse events. It uses specific escape sequences known to work with terminal emulators that tend to share features with xterm. As for how vty-unix determines that you're running a sufficiently "xterm-like" terminal to use the XTermColor backend, it just looks at the value of TERM: if it starts with "xterm" or "screen" then that backend is used. If not, a terminfo-based backend is used, which has a smaller feature set that makes more conservative assumptions about what the terminal supports.

While terminfo does have some capability fields for mouse-related functionality, there are a couple of things about that which make it difficult to support mouse input via terminfo alone: 1) not all terminfo profiles for terminals actually report all the required capabilities (see here for a complete list) and 2) IIRC, terminfo's set of capabilities doesn't cover the range of functionality that vty-unix wants.

What that means in practice is that terminfo alone is not enough (sadly!) to convince vty-unix that the terminal supports much of anything (especially mouse input) so we need to use other (admittedly less-than-ideal) heuristics to determine what we can assume about a given terminal emulator. It's a mess. But then again, the whole world of terminals is a mess in so many ways.

With all that said, one option is for us to modify vty-unix so that TERM=foot (or whatever it is) triggers vty-unix to use the XTermColor backend. This will only work (well) if foot really does honor all the same escape sequences that xterm does. That's usually a safe bet, but these days people are building new terminal emulators that may choose to omit particular features (e.g. out of a desire to reduce perceived bloat).

But before we make such a change, I'd want to see whether things will work; at least for your application, you could simply try running your application with TERM set accordingly to see if it's well-behaved:

$ TERM=xterm my-app

and let me know what you find!