feat(fzf.vim): Adding option g:fzf_fullscreen_layout

[alps2006]

The behavior of fzf Command! (fullscreen) has some differences between Vim and Neovim.

In Neovim, it create a new tab to cause some exceptions when using vimspector (but Vim does not).

puremourning/vimspector#771

This option g:fzf_fullscreen_layout can customize the fullscreen layout as you like. Below is an example:

    if has('nvim')
        let g:fzf_layout = { 'window': { 'width': 1, 'height': 0.4, 'relative': v:true, 'xoffset': 0, 'yoffset': 1 } }
        let g:fzf_fullscreen_layout = { 'window': { 'width': 1, 'height': 1, 'relative': v:false, 'xoffset': 0, 'yoffset': 1 } }
    else
        if exists('$TMUX')
            " See `fzf-tmux --help` for available options
            let g:fzf_layout = { 'tmux': '-p99%,40% -y 60%' }
            let g:fzf_fullscreen_layout = { 'tmux': '-p99%,96% -y 4%' }
        endif
    endif

[junegunn]

I have no experience with the plugin and I don't use Neovim, so I'm not sure what's going on, but I don't quite understand how opening a tab, which is a mundane operation, would cause a problem. Shouldn't it be addressed by the plugin?

[alps2006]

I think this option is very useful in some situations. Below is an operation in Neovim that create a new tab.

[junegunn]

Your primary motivation for this new configuration variable is to work around the vimspector problem, so I insist that the original problem be fixed first. After that, we can discuss whether we really need a new variable here.

I have read through the discussion you linked above (puremourning/vimspector#771), and it doesn't sound like an unfixable problem. Do we have to rely on tab numbers? Can we set up a tab-local variable (t:something) on the relevant tab and loop through the existing tabs (range(1, tabpagenr('$')) to find the one with the variable using gettabvar()?

[alps2006]

Thanks for your advice. I will resolve the problem first.