partially revert f08e8514 (#209)

Deepcopying default config is not reverted . And now user config is always applied on top of default_config. Functionaly it should be same as before f98e8514

lua/lualine/init.lua

@@ -2,17 +2,11 @@
 -- MIT license, see LICENSE for more details.
 local utils_section = require('lualine.utils.section')
 local highlight = require('lualine.highlight')
-local config = vim.deepcopy(require('lualine.defaults'))
+local config = {}
 
 local function apply_configuration(config_table)
   if not config_table then return end
   local function parse_sections(section_group_name)
-    if section_group_name ~= 'options' then
-      config[section_group_name] = {} -- clear old config
-    else
-      -- reset options
-      config.options = vim.deepcopy(require'lualine.defaults'.options)
-    end
     if not config_table[section_group_name] then return end
     for section_name, section in pairs(config_table[section_group_name]) do
       config[section_group_name][section_name] =
@@ -32,7 +26,7 @@ local function apply_configuration(config_table)
   parse_sections('sections')
   parse_sections('inactive_sections')
   parse_sections('tabline')
-  config.extensions = config_table.extensions or {}
+  if config_table.extensions then config.extensions = config_table.extensions end
 end
 
 local function check_single_separator()
@@ -285,8 +279,9 @@ local function set_statusline()
 end
 
 local function setup(user_config)
-  if not user_config then apply_configuration(vim.g.lualine) end
-  apply_configuration(user_config)
+  config = vim.deepcopy(require'lualine.defaults')
+  if user_config then apply_configuration(user_config)
+  elseif vim.g.lualine then apply_configuration(vim.g.lualine) end
   check_single_separator()
   setup_theme()
   load_components()