Re: [multi-tty] Odd regression in vcursor mode in terminal

[Karoly Lorentey]

csant wrote:
> Taking the freedom to report bugs specific to the multi-tty branch
> directly to the emacs-devel list  -  I noticed an odd regression with
> vcursor in the multi-tty branch .  I have managed to boil it down to
> this snippet from my ~/.emacs :
> 
>     (setq vcursor-key-bindings 't)
>     (load "vcursor")
>     (xterm-mouse-mode 1)
> 
> When loading this in ~/.emacs on a startup with
>     $ ./src/emacs -nw
> of a fresh compile of a checkout of the multi-tty branch, C-S-up
> produces the character `A' instead of vcursor-previous-line . However,
> when starting
>     $ ./src/emacs -Q -nw
> and then finding that file and doing a `M-x eval-last-sexp' on each of
> the three items above, everything works as expected .  Also running in X
> gives no problems .

This doesn't seem related to vcursor at all.  The simplest way to reproduce this
that I could find is just having the following in .emacs:

        (load-library "xt-mouse")

The bug is caused by some problem related to `local-function-key-map' during
terminal initialization.  .emacs is loaded *before* term/xterm.el sets up the
local-function-key-map on the terminal, and apparently changing
`function-key-map' before that breaks function keys.

I think this may be related to keymap inheritance.  On the multi-tty branch,
`function-key-map' is the common parent of all terminal-local keymaps
(`local-function-key-map').  To speed up terminal initialization, term/xterm.el
prepares a third keymap with the terminal-dependent function keys (such as
`xterm-function-map'), and set a copy of that as the intermediate parent of
`local-function-key-map'.  The result is as follows:

        function-key-map
        ^
        |
        anonymous copy of xterm-function-map
        ^
        |
        local-function-key-map

Xterm-mouse-mode simply adds a new define-key in function-key-map.  Apparently
this doesn't work right when it does this before the above chain is created.
`local-function-key-map' is different depending on whether xt-mouse is loaded
before or after terminal initialization.  This shouldn't happen.

Unfortunately, I don't have time to debug this now.  I'll return to this later,
unless somebody else fixes it in the meantime.  (It is very much possible that I
simply misunderstood how keymap inheritance works when I wrote the above code.)

-- 
Karoly