refactor(renderer): line creation into a builder pattern

- use a builder pattern to mount the lines / highlights
- i think we lost a little performance, but gain in design
- code for file/folder icons is abstracted in components/icons.lua
- should also fix the issues where vim.g variables where loaded before
  setup.

lua/nvim-tree/renderer/components/icons.lua

@@ -0,0 +1,120 @@
+local icon_config = require "nvim-tree.renderer.icon-config"
+
+local M = { i = {} }
+
+local function config_symlinks()
+  M.i.symlink = #M.icons.symlink > 0 and M.icons.symlink .. M.padding or ""
+  M.i.symlink_arrow = vim.g.nvim_tree_symlink_arrow or " ➛ "
+end
+
+local function empty()
+  return ""
+end
+
+local function get_trailing_length()
+  return vim.g.nvim_tree_add_trailing and 1 or 0
+end
+
+local function set_folder_hl_default(line, depth, git_icon_len, _, hl_group, _, hl)
+  table.insert(hl, { hl_group, line, depth + git_icon_len, -1 })
+end
+
+local function get_folder_icon(open, is_symlink, has_children)
+  local n
+  if is_symlink and open then
+    n = M.icons.folder_icons.symlink_open
+  elseif is_symlink then
+    n = M.icons.folder_icons.symlink
+  elseif open then
+    if has_children then
+      n = M.icons.folder_icons.open
+    else
+      n = M.icons.folder_icons.empty_open
+    end
+  else
+    if has_children then
+      n = M.icons.folder_icons.default
+    else
+      n = M.icons.folder_icons.empty
+    end
+  end
+  return n .. M.padding
+end
+
+local function set_folder_hl(line, depth, icon_len, name_len, hl_icongroup, hl_fnamegroup, hl, should_hl_opened_files)
+  local hl_icon = should_hl_opened_files and hl_icongroup or "NvimTreeFolderIcon"
+  table.insert(hl, { hl_icon, line, depth, depth + icon_len })
+  table.insert(hl, { hl_fnamegroup, line, depth + icon_len, depth + icon_len + name_len + get_trailing_length() })
+end
+
+local function get_file_icon_default(_, _, line, depth, hl)
+  local hl_group = "NvimTreeFileIcon"
+  local icon = M.icons.default
+  if #icon > 0 then
+    table.insert(hl, { hl_group, line, depth, depth + #icon + 1 })
+  end
+  return #icon > 0 and icon .. M.padding or ""
+end
+
+local function get_file_icon_webdev(fname, extension, line, depth, hl)
+  local icon, hl_group = M.devicons.get_icon(fname, extension)
+  if not M.webdev_colors then
+    hl_group = "NvimTreeFileIcon"
+  end
+  if icon and hl_group ~= "DevIconDefault" then
+    if hl_group then
+      table.insert(hl, { hl_group, line, depth, depth + #icon + 1 })
+    end
+    return icon .. M.padding
+  elseif string.match(extension, "%.(.*)") then
+    -- If there are more extensions to the file, try to grab the icon for them recursively
+    return M.get_file_icon(fname, string.match(extension, "%.(.*)"), line, depth, hl)
+  else
+    return get_file_icon_default(fname, extension, line, depth, hl)
+  end
+end
+
+local function config_file_icon()
+  if M.configs.show_file_icon then
+    if M.devicons then
+      M.get_file_icon = get_file_icon_webdev
+    else
+      M.get_file_icon = get_file_icon_default
+    end
+  else
+    M.get_file_icon = empty
+  end
+end
+
+local function config_special_icon()
+  if M.configs.show_file_icon then
+    M.i.special = #M.icons.default > 0 and M.icons.default .. M.padding or ""
+  else
+    M.i.special = ""
+  end
+end
+
+local function config_folder_icon()
+  if M.configs.show_folder_icon then
+    M.get_folder_icon = get_folder_icon
+    M.set_folder_hl = set_folder_hl
+  else
+    M.get_file_icon = empty
+    M.set_folder_hl = set_folder_hl_default
+  end
+end
+
+function M.reset_config(webdev_colors)
+  M.configs = icon_config.get_config()
+  M.icons = M.configs.icons
+  M.padding = vim.g.nvim_tree_icon_padding or " "
+  M.devicons = M.configs.has_devicons and require "nvim-web-devicons" or nil
+  M.webdev_colors = webdev_colors
+
+  config_symlinks()
+  config_special_icon()
+  config_file_icon()
+  config_folder_icon()
+end
+
+return M