mouse not works in builtin terminal for ncurses app

[haolian9]

Neovim version (nvim -v)

NVIM v0.8.0

Vim (not Nvim) behaves the same?

not tested

Operating system/version

archlinux

Terminal name/version

xterm 375

$TERM environment variable

in xterm it is xterm, in nvim terminal it is xterm-256color

Installation

system package manager

How to reproduce the issue

• $ xterm
• $ nvim --clean +'terminal nnn' # https://github.com/jarun/nnn
• $ nvim --clean +'terminal tig' # https://github.com/jonas/tig

Expected behavior

mouse works in nvim's builtin terminal for ncurses app;

Actual behavior

mouse left, right click and scroll up, down do not work as expected, and the two programs are ncurses based.
if I run them in xterm directly, the mouse works well.

more tests

If i do as this, then the mouse works well:

• $ xterm
• `$ nvim --clean +'terminal'
• $ echo '\x1b[?1002h # now we are in nvim's builtin terminal
• $ nnn

[zeertzjq]

It seems that when $TERM is xterm or xterm-256color, nnn sends \x1b[?1006;1000h to enable mouse, which seems not recognized by libvterm. When $TERM is something else it sends \x1b[?1000h to enable mouse. So a workaround is to set $TERM to something else when running nnn.

[zeertzjq]

From curs_mouse(3X):

       If the terminfo entry contains a XM string, this is used in the xterm mouse driver to control the way the terminal is initialized for mouse operation.  The default, if  XM  is  not
       found, corresponds to private mode 1000 of xterm:

          \E[?1000%?%p1%{1}%=%th%el%;

       The mouse driver also recognizes a newer xterm private mode 1006, e.g.,

          \E[?1006;1000%?%p1%{1}%=%th%el%;

From user_caps(5):

             Here are examples from the terminal database for the most commonly used xterm mouse protocols:

               xterm+x11mouse|X11 xterm mouse protocol,
                       kmous=\E[M, XM=\E[?1000%?%p1%{1}%=%th%el%;,
                       xm=\E[M
                          %?%p4%t%p3%e%{3}%;%' '%+%c
                          %p2%'!'%+%c
                          %p1%'!'%+%c,

               xterm+sm+1006|xterm SGR-mouse,
                       kmous=\E[<, XM=\E[?1006;1000%?%p1%{1}%=%th%el%;,
                       xm=\E[<%i%p3%d;
                          %p1%d;
                          %p2%d;
                          %?%p4%tM%em%;,

So it indeed seems to be xterm-256color causing the problem here.

[haolian9]

a bit off-topic, i'm amazed by your debugging skill, could you share how you know nnn sends \x1b[?1006;1000h?
Minutes later, i managed to do it with strace -o file nnn, but i'm still wondering the way you used.

[zeertzjq]

I was just using script.

[haolian9]

It seems that when $TERM is xterm or xterm-256color, nnn sends \x1b[?1006;1000h to enable mouse

confirmed.

... which seems not recognized by libvterm. a workaround is to set $TERM to something else like tmux-256color

I saw centos 7 does not has tmux-256color terminfo. oh i see, maybe libvterm uses its own xterm-256color terminfo which does not match the one provided by the system?

[zeertzjq]

libvterm itself by default does not seem to set $TERM variable. Nvim sets it to xterm-256color in termopen()

[haolian9]

that explains why the TERM workaround works in some terminal emulators for nnn used by nnn.nvim, while in some other terminals, it does not. eg. xterm, konsole.
If i need to set the TERM env, maybe the screen-256color is the most well-supported option for this case.

[erw7]

So a workaround is to set $TERM to something else like tmux-256color when running nnn.

Do not suggest as a workaround an improper method that sets $TERM to an incorrect value. That workaround will create a new problem where the Home and End key will not work. You know that issue tracker of neovim also contains a lot of issues when $TERM is set to the wrong value.

A more appropriate workaround is to send a sequence that enables mouse input before invoking nnn, such as using a function like the following:

function nnn() {
  printf "\x1b[?1000h"
  /usr/bin/nnn ${1+"$@"}
  printf "\x1b[?1000l"
}

[erw7]

There doesn't seem to be much discussion about this. Vim's :terminal already lets :terminal inherit $TERM, while in Nvim $TERM has always been xterm-256color in :terminal since it was first added in #2076, and there doesn't seem to be discussion about this in #2076 either.

Regardless of the host terminal, neovim terminals always behave like xterm. Therefore, it is inappropriate to inherit $TERM without discussion.

It is clear from the following code that vim inherits $TERM only if it starts with xterm. It may be debatable whether to implement the same in neovim. However, as far as I know, the only recent terminal where xterm is appropriate for $TERM and 256 colors are not available is the FreeBSD console. Thus I see little need to implement it.

Ref. https://github.com/vim/vim/blob/ce30ccc06af7f2c03762e5b18dde37b26ea6ec42/src/os_unix.c#L5638-L5640

// Use 'term' or $TERM if it starts with "xterm", otherwise fall
// back to "xterm" or "xterm-color".
if (term == NULL || *term == NUL || STRNCMP(term, "xterm", 5) != 0)

[justinmk]

vim inherits $TERM only if it starts with xterm. It may be debatable whether to implement the same in neovim

Yep. Makes no sense for :terminal to claim it is some other $TERM (except perhaps something custom like xterm-nvim, but really, it's better if we just aim to be a satisfactory implementation of xterm and claim xterm-256color).

Child processes can check $NVIM to confirm that they are running in :terminal.

[vlada-dudr]

Isn't correct solution to claim TERM=nvim and provide appropriate terminfo (and maybe termcap) databases? Maybe providing several entries and setting correct one depending on features of parent terminal, like nvim-256color and nvim-truecolor.

[neovim-discourse]

This issue has been mentioned on Neovim Discourse. There might be relevant details there:

https://neovim.discourse.group/t/how-can-i-enable-the-mouse-for-the-programs-i-run-on-the-terminal/4016/5

[Zeioth]

For terminal progams this has to be setted:

set mouse=a
printf "\x1b[?1000h"

But for for the actual terminal, to enable mouse support one must

set mouse=""
printf "\x1b[?1000l"

Then to make the mouse work on neovim one must

set mouse=a

All this work, but it is super hackish. What if we make a neovim option to do all this stuff for the user? I don't think the average user is gonna be willing to go through all of this just to have mouse support.

The issue is this may not work for all terminals, but most modern terminals are xterm-256color, so it should be fine.

I can think 3 solutions to this border case:

• Give the user options to set the term codes.
• We detect the term and set the codes automatically.
• We just let the user opt-out the mouse support and be on its own.

[zeertzjq]

Applying the following patch to libvterm may fix this issue:

diff --git a/src/libvterm/src/state.c b/src/libvterm/src/state.c
index ee4482469..478b1317c 100644
--- a/src/libvterm/src/state.c
+++ b/src/libvterm/src/state.c
@@ -1370,8 +1370,9 @@ static int on_csi(const char *leader, const long args[], int argcount, const cha
     break;
 
   case LEADER('?', 0x68): // DEC private mode set
-    if(!CSI_ARG_IS_MISSING(args[0]))
-      set_dec_mode(state, CSI_ARG(args[0]), 1);
+    for (int i = 0; i < argcount; i++)
+      if(!CSI_ARG_IS_MISSING(args[i]))
+        set_dec_mode(state, CSI_ARG(args[i]), 1);
     break;
 
   case 0x6a: // HPB - ECMA-48 8.3.58
@@ -1392,8 +1393,9 @@ static int on_csi(const char *leader, const long args[], int argcount, const cha
     break;
 
   case LEADER('?', 0x6c): // DEC private mode reset
-    if(!CSI_ARG_IS_MISSING(args[0]))
-      set_dec_mode(state, CSI_ARG(args[0]), 0);
+    for (int i = 0; i < argcount; i++)
+      if(!CSI_ARG_IS_MISSING(args[i]))
+        set_dec_mode(state, CSI_ARG(args[i]), 0);
     break;
 
   case 0x6d: // SGR - ECMA-48 8.3.117

But I don't know if this change is desired.

[Zeioth]

@zeertzjq I've:

• uninstalled libvterm on my system
• downloaded and patched libvterm from here
• sudo make install

I don't see any change of behavior on nvim term. I'm not sure what is supposed to happen.

[zeertzjq]

Works for me using extra/neovim and AUR neovim-git packages. If you are using AUR neovim-nightly-bin then it will not work.

[Zeioth]

Neovim installed from extra

libvterm patched

How I've tested

• Open neovim
• :term → No changes
• ranger → No changes

Questions

What terminal are you running neovim on? I'm using foot terminal with xterm256color.