docs: Update readme with code that works for resizable filetrees

[airtonix]

NvimTree and neo-tree are both resizable, this just shows how a user can get that information and use it.

fixes #373

Screencast from 2023-03-02 17-21-53.webm

[romgrk]

Thanks, can you adjust the code to use the same conventions we use in this repo? In particular:

• 2 spaces indentation
• snake_case

And I'm wondering if we should add examples for each tree plugin, or maybe keep them in an examples/ folder and link to them.

[Iron-E]

Before merging, I want to double check that nvim_create_autocmd doesn't expose the information being worked around in get_filetree_window. Iirc it does, but we'll see

examples folder

Not a bad idea. It would also let the LSP attach when adjusting the examples,which prevents syntax errors.

I think there should be one examples/general.lua for the common case (e.g. NvimTree, neo-tree) since they seem to be compatible.

[Iron-E]

@airtonix I've taken a look, and it seems nvim_create_command puts out the information you need to do resizing. Here's what you can put into the README:

vim.api.nvim_create_autocmd('FileType', {
  callback = function(tbl)
    local api = require'bufferline.api'
    local autocmd = vim.api.nvim_create_autocmd('WinScrolled', {
      buffer = tbl.buf,
      callback = function()
        local width = vim.api.nvim_win_get_width(vim.fn.bufwinid(tbl.buf))
        api.set_offset(width, 'FileTree')
      end,
    })

    vim.api.nvim_create_autocmd('BufWipeout', {
      buffer = tbl.buf,
      callback = function()
        vim.api.nvim_del_autocmd(autocmd)
        api.set_offset(0)
      end,
      once = true,
    })
  end,
  pattern = 'NvimTree', -- or any other filetree's `&ft`
})

This implementation is actually more performant than the existing one, since it registers buf-local or patterned autocmds (instead of a global autocmd for every buffer created). It also destroys autocmds when the tree is closed

[Iron-E]

Thank you!