can the filename include the folder?

[NullVoxPopuli]

in many projects (web, esp) there are "index" files, it'd be nice to be able to configure having the folder show up so there is some context as to which index file

[b0o]

Absolutely! I wanted this recently too after working with the Next.js App Router. Here are some helper functions:

local incline = require 'incline'
local Path = require 'plenary.path'

--- Given a path, return a shortened version of it.
--- @param path string an absolute or relative path
--- @param opts table
--- @return string | table
---
--- The tail of the path (the last n components, where n is the value of
--- opts.tail_count) is kept unshortened.
---
--- Each component in the head of the path (the first components up to the tail)
--- is shortened to opts.short_len characters.
---
--- If opts.head_max is non-zero, the number of components in the head
--- is limited to opts.head_max. Excess components are trimmed from left to right.
--- If opts.head_max is zero, all components are kept.
---
--- opts is a table with the following keys:
---   short_len: int - the number of chars to shorten each head component to (default: 1)
---   tail_count: int - the number of tail components to keep unshortened (default: 2)
---   head_max: int - the max number of components to keep, including the tail
---     components. If 0, keep all components. Excess components are
---     trimmed starting from the head. (default: 0)
---   relative: bool - if true, make the path relative to the current working
---     directory (default: true)
---   return_table: bool - if true, return a table of { head, tail } instead
---     of a string (default: false)
---
--- Example: get_short_path_fancy('foo/bar/qux/baz.txt', {
---   short_len = 1,
---   tail_count = 2,
---   head_max = 0,
--- }) -> 'f/b/qux/baz.txt'
---
--- Example: get_short_path_fancy('foo/bar/qux/baz.txt', {
---   short_len = 2,
---   tail_count = 2,
---   head_max = 1,
--- }) -> 'ba/baz.txt'
---
local function shorten_path(path, opts)
  opts = opts or {}
  local short_len = opts.short_len or 1
  local tail_count = opts.tail_count or 2
  local head_max = opts.head_max or 0
  local relative = opts.relative == nil or opts.relative
  local return_table = opts.return_table or false
  if relative then
    path = vim.fn.fnamemodify(path, ':.')
  end
  local components = vim.split(path, Path.path.sep)
  if #components == 1 then
    if return_table then
      return { nil, path }
    end
    return path
  end
  local tail = { unpack(components, #components - tail_count + 1) }
  local head = { unpack(components, 1, #components - tail_count) }
  if head_max > 0 and #head > head_max then
    head = { unpack(head, #head - head_max + 1) }
  end
  local result = {
    #head > 0 and Path.new(unpack(head)):shorten(short_len, {}) or nil,
    table.concat(tail, Path.path.sep),
  }
  if return_table then
    return result
  end
  return table.concat(result, Path.path.sep)
end

--- Given a path, return a shortened version of it, with additional styling.
--- @param path string an absolute or relative path
--- @param opts table see below
--- @return table
---
--- The arguments are the same as for shorten_path, with the following additional options:
---   head_style: table - a table of highlight groups to apply to the head (see
---      :help incline-render) (default: nil)
---   tail_style: table - a table of highlight groups to apply to the tail (default: nil)
---
--- Example: get_short_path_fancy('foo/bar/qux/baz.txt', {
---   short_len = 1,
---   tail_count = 2,
---   head_max = 0,
---   head_style = { guibg = '#555555' },
--- }) -> { 'f/b/', guibg = '#555555' }, { 'qux/baz.txt' }
---
local function shorten_path_styled(path, opts)
  opts = opts or {}
  local head_style = opts.head_style or {}
  local tail_style = opts.tail_style or {}
  local result = shorten_path(
    path,
    vim.tbl_extend('force', opts, {
      return_table = true,
    })
  )
  return {
    result[1] and vim.list_extend(head_style, { result[1], '/' }) or '',
    vim.list_extend(tail_style, { result[2] }),
  }
end

Example usage:

incline.setup {
  render = function(props)
    return shorten_path_styled(vim.api.nvim_buf_get_name(props.buf), {
      short_len = 1,
      tail_count = 2,
      head_max = 4,
      head_style = { group = 'Comment' },
      tail_style = { guifg = 'white' },
    })
  end,
}

[marcelarie]

Should this be implemented by default? I think showing the full path is really useful.

    render = function(p)
        local full_path = vim.api.nvim_buf_get_name(p.buf)
        return full_path:gsub(vim.fn.getcwd(), ".")
    end,

[andrhua]

to have indicator whether buffer is modified

local function modified_suffix(buf)
  if vim.api.nvim_buf_get_option(buf, 'modified') then
    return ' [+]'
  else
    return ''
  end
end

-- change signature of shorten_path_styled to accept buf instead of path
local function shorten_path_styled(buf, opts)
  local path = vim.api.nvim_buf_get_name(buf)
  ... -- the rest is unchanged except for the returned table
  return {
    result[1] and vim.list_extend(head_style, { result[1], '/' }) or '',
    vim.list_extend(tail_style, { result[2] }),
    modified_suffix(buf) -- add this
  }
end

-- and finally pass buf in render function
incline.setup {
  ...
  render = function(props)
    return shorten_path_styled(props.buf, {
    ...