How to setup tabline separators like in lightline

[segeljakt]

Hi, I am migrating from lightline and trying to figure out to add these types of separators:

I tried using surround, but it seems to be more well-suited for surrounding characters like ( ). I would like to use the single-character separators for the bufferline.

Do you have any recommendations on how it might be implemented with heirline?

[rebelot]

so, it is possible, but requires a bit of effort to pull it off nicely.. here it goes:

-- initialise the handle for the buflist. This will be an array of bufnumbers.
-- define a couple of utility functions to check if the component is at the end of the buflist,
-- of if it is right before the active buffer
local bufcache = {}
local function is_last(bufnr)
    return bufcache[#bufcache] == bufnr
end
local function is_before_active(bufnr)
    for i, b in ipairs(bufcache) do
        if b == bufnr then
            return vim.api.nvim_get_current_buf() == bufcache[i + 1]
        end
    end
end

local TablineBufferBlock = {
    {
        condition = function(self)
            return self.is_active
        end,
        hl = { bg = "white" },
        {
            provider = " ", -- right full chevron (green on white)
            hl = { fg = "green", bg = "white" },
        },
        { TablinePicker, TablineFileNameBlock, TablineCloseButton },
        {
            provider = " ", -- right full chevron (white on green/none)
            hl = function(self)
                if is_last(self.bufnr) then
                    return { fg = "white", bg = "none" }
                else
                    return { fg = "white", bg = "green" }
                end
            end,
        },
    },
    {
        condition = function(self)
            return not self.is_active
        end,
        hl = { bg = "green" },
        { TablinePicker, TablineFileNameBlock, TablineCloseButton },
        {
            init = function(self)
                self.provider = "" -- reset the provider to an empty string
                if is_last(self.bufnr) then
                    self.provider = " " -- full right chevron (green on none)
                    self.hl = { fg = "green", bg = "none" }

                elseif not is_before_active(self.bufnr) then
                    self.provider = " " -- thin right chevron (white on green)
                    self.hl = { fg = "white", bg = "green" }
                end
            end,
        },
    },
}

local BufferLine = utils.make_buflist(
    TablineBufferBlock,
    { provider = " ", hl = { fg = "gray" } },
    { provider = " ", hl = { fg = "gray" } },
    nil,
    bufcache
)

The difficulty here lies in the fact that both separators and their highlights depend on the current buffer and their relative/absolute position in the buflist. This is much easier to do in the statusline/winbar where fields are usually static

HTH

[segeljakt]

Thank you for the excellent answer. One minor tweak I made was to add a condition so that it only adds a chevron before the current buffer if that buffer is not the first one in the list.

Another question I have, is it possible to support this but for tabpages also like in Lightline? In Lightline there is a configuration that shows the filename of the current buffer of the current window per tabpage.

I tried this so far:

local TabpageFileFlags = {
  {
    condition = function(self)
      return vim.api.nvim_buf_get_option(self.bufnr, "modified")
    end,
    provider = "+ ",
  },
  {
    condition = function(self)
      return not vim.api.nvim_buf_get_option(self.bufnr, "modifiable")
          or vim.api.nvim_buf_get_option(self.bufnr, "readonly")
    end,
    provider = function(self)
      if vim.api.nvim_buf_get_option(self.bufnr, "buftype") == "terminal" then
        return "  "
      else
        return ""
      end
    end,
    hl = { fg = "orange" },
  },
}

local TabpageName = {
  provider = function(self)
    return vim.fn.fnamemodify(vim.api.nvim_buf_get_name(self.bufnr), ":t")
  end
}

local function is_last_tab(tabnr)
  local tabpages = vim.api.nvim_list_tabpages()
  return tabpages[#tabpages] == tabnr
end

local function is_before_active_tab(tabnr)
  local tabpages = vim.api.nvim_list_tabpages()
  for i, t in ipairs(tabpages) do
    if t == tabnr then
      return vim.api.nvim_get_current_buf() == tabpages[i + 1]
    end
  end
end

local Tabpage = {
  init = function(self)
    local winnr = vim.api.nvim_tabpage_get_win(self.tabnr)
    self.bufnr = vim.api.nvim_win_get_buf(winnr)
  end,
  {
    condition = function(self)
      return self.is_active
    end,
    hl = { bg = "white" },
    {
      provider = " ", -- right full chevron (green on white)
      hl = { fg = "green", bg = "white" },
    },
    { TabpageName, TabpageFileFlags },
    {
      provider = " ", -- right full chevron (white on green/none)
      hl = function(self)
        if is_last_tab(self.tabnr) then
          return { fg = "white", bg = "none" }
        else
          return { fg = "white", bg = "green" }
        end
      end,
    },
  },
  {
    condition = function(self)
      return not self.is_active
    end,
    hl = { bg = "green" },
    { TabpageName, TabpageFileFlags },
    {
      init = function(self)
        self.provider = "" -- reset the provider to an empty string
        if is_last_tab(self.bufnr) then
          self.provider = " " -- full right chevron (green on none)
          self.hl = { fg = "green", bg = "none" }

        elseif not is_before_active_tab(self.bufnr) then
          self.provider = " " -- thin right chevron (white on green)
          self.hl = { fg = "white", bg = "green" }
        end
      end,
    },
  },
}

local Tabline = require("heirline.utils").make_tablist(Tabpage)

A problem I run into is that once I start closing tabs the self.tabnr becomes invalid. Once that happens any calls to calculate the winnr and bufnr throws an exception. Do you have any ideas or recommendations?

[rebelot]

you should use but_func argument to make_buflist for this. You can pass a function that returns bufnrs of the current tab. Be aware that there is a difference between tab number and tab id (as for winnr and winid).