Re: ZLE Vi-mode: visual mode selection doesn't match the characters highlighted

[Doron Behar <doron.behar@gmail.com>]

On Wed, Oct 16, 2019 at 09:37:50PM +0200, Oliver Kiddle wrote:
> On 13 Oct, Doron Behar wrote:
> > Thanks for suggesting that. Indeed this is a combination of terminal
> > emulators' settings / differences in behaviour along with a certain
> > plugin I use: https://github.com/zsh-users/zsh-syntax-highlighting
> 
> If I run zsh -df and then enable just that plugin by doing
>   . zsh-syntax-highlighting.zsh
> then I still can't reproduce the problem with highlighting of the t.
>
> It doesn't appear to create any new keymaps so I'm unsure why you
> don't get the `t' highlighted. Are you loading it with a plugin
> manager? It'd be useful to isolate just the minimum required to
> cause the problem.

I'm glad Oliver that you are attending _this_ issue as well but I'd like
to deal with it at that GitHub thread
(https://github.com/zsh-users/zsh-syntax-highlighting/issues/637), as I
don't feel it's related and focus here on the _cursor's_ character's
highlighting.

Never the less, I'll emphasize that this issue appears only when the
syntax highlighter colors the text of `t` in a certain foreground color.
If normal foreground color is used, `t` is highlighted properly.

> Zsh does highlight the cursor position. It is down to the terminal
> emulator how that appears. What terminal emulator do you use? What is
> $TERM set to and what OS are you on? I use a green solid block as my
> cursor and I know that the cursor position is included in the
> selection.  It appears much the same in vim and gvim.

I'm using NixOS and our `urxvt` is compiled according to this "recipe":

https://github.com/NixOS/nixpkgs/blob/7885eeaffdbd02ff6ce5483239fba1a063b314a9/pkgs/applications/misc/rxvt_unicode/default.nix

My `$TERM` is `rxvt-unicode-256color`.

I've tested as well: 

- Urxvt with an empty `.Xresources` (I ran `xrdb merge .Xresources`)
- Gnome-Terminal
- Konsole

I've demonstrated the problematic behaviour with `zsh -df` (without
syntax highlighting) here:

https://gist.github.com/doronbehar/cba65dbac52b5859e8e967a6bc71ea91#gistcomment-3057815

As you can see, if the cursor's color is not blinking, **all** tested
terminal emulators don't highlight the cursor's character.

I dearly hope the issue is clear now.

> You may be able to configure the cursor with escape sequences. For
> example, for a vertical bar (good for vi insert mode):
>   print -n $'\e[5 q'

I tried using an underline cursor, and it somewhat improved my
situation: The letter the cursor is standing at is highlighted so it's a
good-enough workaround but I hope this won't be considered as a solution
because in general, I prefer the block cursor.

> We could perhaps use some hooks for when visual mode is invoked and
> finished.

Yea I can use `zle-keymap-select` in the meantime...

> > Oliver, do you think perhaps ZSH could 'double reverse' the cursor
> > in visual mode? I think this will emulate Vim's behaviour better
> > because this way, with a non blinking cursor in visual mode, the
> > character the cursor stands upon will standout as well.
> 
> That could make it hard to see which end of the selection the cursor
> is at.

I can imagine, but if the cursor is a block and it's not blinking, no
sane user would expect to see on which end of the selection the cursor's
located since the cursor is a block. Vim can't help you distinguish this
as well.

With the current behaviour and a non blinking, block cursor, it's even
more confusing if the character the cursor is located at is not
highlighted at all but it _is_ selected!

> Whatever highlighting is chosen, there will be some terminal
> setup for which it is not ideal and somebody who complains.

I hope I've demonstrated good enough that this is not a terminal
emulator issue, it's an issue of a non blinking cursor. Hence, I think
my complain is legitimate.

> Vim's defaults result in a barely visible selection if you chose a
> near-white default background colour.

I'm not sure I agree. I tested Vim in Konsole and Gnome terminal and the
cursor was surely visible - a black block on a white or whitish
background instead of the other way around.

> Copying Vim might be tempting but Vim is not the only editor - zsh
> uses the term region for the selection in many cases because the
> feature first appeared in an Emacs form.

I'm not sure how emacs feels in that sense, nor ZSH's region selection
when it's emulating Emacs. Anyhow, since there are only 2 editors we
emulate, I think Vim should be emulated if `bindkey -v` is set, else
Emacs should be emulated.

> Feel free to lobby on zsh-workers if you want the defaults changed.
> Personally I was happy to just tweak zle_highlight and the terminal
> emulator.

I'd love to lobby there but I'm not sure what defaults can I change.
Given the GIF demonstrations I've made. It seems to me the underlying
code needs a change, and that the defaults are OK.

I'd thank you a lot Oliver if you'll at least verify that with your
version of ZSH and the terminals I tested you get the same behaviour
with a non blinking cursor.

Thanks, Doron.