Using vim mappings in normal :terminal mode

Question

I'm using vim and configured :terminal with bash and vi-mode. To do that I've configured .inputrc config from: https://vim.fandom.com/wiki/Use_vi_shortcuts_in_terminal. I've noticed that my keybindings don't cooperate with bindings in the terminal. Eg. I'm switching buffers with <TAB>. That keybinding doesn't distinguish whether bash in :terminal is in insert or normal mode so I need to type <C-w>w to go forward. When I use following mapping in my .vimrc:

tmap <TAB> <C-w>w

then I cannot use tab anymore when bash in my :terminal is in insert mode. Vim uses tmap mappings for both vi-modes insert and normal modes.

Is this possible to have <TAB> switching the buffer only when bash in :terminal is in normal mode and <TAB> doing autocompletion when bash in :terminal is in the insert mode?

Answer 1

Vim can't really tell whether the bash shell inside its terminal is running in vi-insert mode or in vi-normal mode. In fact, it can't even tell whether it's using vi or emacs mode. Or at some moments, while you're running a command inside bash, it doesn't even make sense to talk about whether bash is in insert or normal mode, since technically it isn't in either...

So to achieve this kind of integration, you'll need to have bash tell Vim about which mode it's in, or similarly, have bash interpret the key-bindings and call Vim commands from bash when the special keys are triggered.

Personally, I think the latter is easiest, doing the key bindings in bash, since last I looked there wasn't really a very reliable to hook into the mode change from bash, or even to reliably detect when a new command was about to be executed. (zsh seems to be much better than bash in this sense, it has more hooks and they're typically easier to use.)

The other piece missing here is to call Vim commands from the shell running inside Vim's terminal. You can do that using the terminal-api, which allows you to use an escape sequence from bash to call a function in Vim.

For the bash bindings, see the bind command, I believe you can pass it a -m to create a binding for a specific mode (such as vi-normal) and you can use -x to execute some code (or a function) when a specific key combination is entered.

For example, this will make <Tab> (which is the same as Ctrl+I) call function wincmd_next() when pressed in vi mode (which matches the "normal" vi mode in readline):

bind -m vi -x '"\C-i": wincmd_next'

For the Vim terminal API, you can export a Tapi_wincmd function that can be called from the shell. Then from bash you should be able to use:

echo -ne '\e]51;["call","Tapi_wincmd",["w"]]\a'

So just turn that into the wincmd_next function:

wincmd_next () {
    echo -ne '\e]51;["call","Tapi_wincmd",["w"]]\a'
}

And then you can write the corresponding Vim function:

function! Tapi_wincmd(bufnum, arglist)
    execute 'wincmd' a:arglist[0]
endfunction

This way, the bash command above will cause Vim to cycle to the next window.

The terminal API takes JSON encoded arguments. By default, only functions named using the Tapi_ prefix are allowed to be called from the terminal API. So you can decide how much and which specific features and parameters you want to expose to terminal applications from Vim.

I believe these pointers should be enough for you to put together everything you need to set up the specific scenario you described, which involves switching Vim windows when Tab is pressed, but only when the shell is in the vi-normal mode.

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An alternative to this approach is to use :tnoremap to hook into keystrokes whenever they're being sent to the application running on the terminal, whether that's bash in vi-normal mode, bash in vi-insert mode or another application altogether.

As you mentioned in the question, you can configure that with:

tnoremap <Tab> <C-w>w

But that doesn't leave you a way to use an actual Tab in the terminal, which might be useful when doing completion in vi-insert (or emacs) mode.

You can work around that by mapping a different keystroke to send an actual Tab to the terminal application, for example, one of:

tnoremap <S-Tab> <Tab>      " Shift-Tab
tnoremap <C-v><Tab> <Tab>   " Ctrl-V, Tab
tnoremap <C-P> <Tab>        " Ctrl-P