[BUG] Some control characters cannot be entered, even using raw insert

[alois31]

Version of Kakoune

v2024.05.18

Reproducer

Try to enter any of the following control characters using raw insert (Ctrl-V):

• null (Ctrl-Space)
• end of text (Ctrl-C)
• bell (Ctrl-G)
• carriage return (Ctrl-M)
• substitute (Ctrl-Z)
• delete (Backspace)

Outcome

The control characters cannot be entered. Specifically, the following happens:

• Ctrl-Space and Backspace close the raw insert hint, but do not actually insert anything.
• Ctrl-C appears to have no effect at all (presumably it invokes the usual "stop external processes" action).
• Ctrl-G only shows an "operation cancelled" message.
• Ctrl-M inserts line feed instead.
• Ctrl-Z stops the editor process.

Expectations

All control characters can be inserted using the raw insert functionality.

Additional information

The issue has been reproduced on NixOS unstable using the Konsole and xterm terminals. On the latter, it is additionally impossible to enter backspace (Ctrl-H).

Relatedly, keys or key combinations that send escape sequences (like arrows, function keys or using Alt) do not work with raw insert mode either. Maybe this is less critical since the sequences could still be entered manually, but the root cause might be the same.