feat(preview): support format_title config

[MunifTanjim]

The current way of doing this is very hacky.

```lua require("bqf.preview.floatwin").generateTitle = function (self, bufnr, idx, size) local position = (" [%d/%d] "):format(idx, size) local buffer = ("buf %d: "):format(bufnr) local flags = vim.bo[bufnr].modified and " [+] " or " " local max_width = self.width - 4 - vim.fn.strwidth(buffer) - vim.fn.strwidth(position) - vim.fn.strwidth(flags) local fname = vim.fn.fnamemodify(vim.fn.bufname(bufnr), ":p:~:.") local attempt = 3 while max_width < vim.fn.strwidth(fname) do if attempt == -1 then fname = "" break elseif attempt == 0 then fname = vim.fn.fnamemodify(fname, ":t") else fname = vim.fn.pathshorten(fname, attempt * 2 - 1) end attempt = attempt - 1 end return ("%s%s%s%s"):format(position, buffer, fname, flags) end ```

This config will enable user to do it cleanly:

local function format_title(info)
  local bufnr = info.bufnr
  local position = (" [%d/%d] "):format(info.idx, info.size)
  local buffer = ("buf %d: "):format(bufnr)
  local flags = vim.bo[bufnr].modified and " [+] " or " "
  local max_width = info.max_width - vim.fn.strwidth(buffer) - vim.fn.strwidth(position) - vim.fn.strwidth(flags)

  local fname = vim.fn.fnamemodify(vim.fn.bufname(bufnr), ":p:~:.")

  local attempt = 3
  while max_width < vim.fn.strwidth(fname) do
    if attempt == -1 then
      fname = ""
      break
    elseif attempt == 0 then
      fname = vim.fn.fnamemodify(fname, ":t")
    else
      fname = vim.fn.pathshorten(fname, attempt * 2 - 1)
    end
    attempt = attempt - 1
  end

  return ("%s%s%s%s"):format(position, buffer, fname, flags)
end

require("bqf").setup({
  preview = {
    format_title = format_title,
  },
})

Outside current directory (under root):

Outside current directory (under home):

Inside current directory:

Truncations:

3:

2:

1:

0:

-1:

[kevinhwang91]

Could you show me your customized title? I'm not sure why the users need it, current title has shown since this plugin release, and no one ask to customize it.

[MunifTanjim]

Could you show me your customized title?

It's mostly like the built-in one. But for files under the current directory, the current directory is stripped out. And the truncation has some additional steps:

• path shorten with 5 chars
• path shorten with 3 chars
• path shorten with 1 chars (existing)
• only filename
• no name (existing)

This shows as much information as possible, as long as possible. Also, the built-in one has a hardcoded 15 width reserved, so sometimes title disappears even when there's room to show it.

I've added the screenshots in PR description.

[kevinhwang91]

Thanks to contribute this plugin, but I think it's not worthy for this. As a maintainer, I don't want to expose unnecessary (few users use) API function to users. I hate breaking change and just want to easy to iterate modules in the future.

[MunifTanjim]

Not sure how giving user more customizability is unnecessary, or how this will lead to breaking change... but it's your call.