Look at ctrl+Fn keys under (u)rxvt

[davep]

One finding of #3440 was that ctrl plus function keys, with rxvt, at least under Xquartz on macOS¹, seems to emit escape sequences that are different from other terminal emulators. Given the approach we want to take of "if commonly-supported keys trigger otherwise-unknown escape sequences, we should support them if they don't conflict with anything else": check that there is no clash with those sequences and add them to Textual.

Footnotes

1. I think on GNU/Linux too. Looking at the recording done, I can't see the ctrl plus functions keys as having been triggered; but neither do I see escape sequences that were emitted. Might need to do a quick re-test of this. Or... @TomJGooding -- I seem to remember you're a GNU/Linux user who's a fan of rxvt, could you confirm? ↩

[davep]

The unknown sequences (that were tested for) are \x1b[11^ thru \x1b[24^. Looking in _ansi_sequences.py there is this:

    "\x1b[11~": (Keys.F1,),  # rxvt-unicode
    "\x1b[12~": (Keys.F2,),  # rxvt-unicode
    "\x1b[13~": (Keys.F3,),  # rxvt-unicode
    "\x1b[14~": (Keys.F4,),  # rxvt-unicode
    "\x1b[15~": (Keys.F5,),
    "\x1b[17~": (Keys.F6,),
    "\x1b[18~": (Keys.F7,),
    "\x1b[19~": (Keys.F8,),
    "\x1b[20~": (Keys.F9,),
    "\x1b[21~": (Keys.F10,),
    "\x1b[23~": (Keys.F11,),
    "\x1b[24~": (Keys.F12,),
    "\x1b[25~": (Keys.F13,),
    "\x1b[26~": (Keys.F14,),
    "\x1b[28~": (Keys.F15,),
    "\x1b[29~": (Keys.F16,),
    "\x1b[31~": (Keys.F17,),
    "\x1b[32~": (Keys.F18,),
    "\x1b[33~": (Keys.F19,),
    "\x1b[34~": (Keys.F20,),

So it would appear that the ctrl-modified function keys under rxvt are the same sequences as unmodified function keys, only ending in ^ rather than ~.

[davep]

Quickly double-checking, ctrl+shift+Fn does also follow the same pattern, albeit after ctrl+shift apparently causing a message to appear about switching to some other mode:

Screen.Recording.2023-11-23.at.11.29.54.mov

As such, I think it's safe to duplicate the unmodified rxvt sequences in the file, swap the ~ for a ^, and we should have all those keys supported too.

A bit of searching online has turned up no good reason why this would be a bad idea.

[davep]

Bonus discovery while testing:

    "\x1b[23@": (Keys.ControlF21,),
    "\x1b[24@": (Keys.ControlF22,),

In other words, ctrl+shift and F11 and F12 mimic F11 and F12 but with @ in the place of ~.

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