add small arrows before folders (#427)

README.md

@@ -56,10 +56,13 @@ let g:nvim_tree_show_icons = {
     \ 'git': 1,
     \ 'folders': 0,
     \ 'files': 0,
+    \ 'folder_arrows': 0,
     \ }
 "If 0, do not show the icons for one of 'git' 'folder' and 'files'
 "1 by default, notice that if 'files' is 1, it will only display
-"if nvim-web-devicons is installed and on your runtimepath
+"if nvim-web-devicons is installed and on your runtimepath.
+"if folder is 1, you can also tell folder_arrows 1 to show small arrows next to the folder icons.
+"but this will not work when you set indent_markers (because of UI conflict)
 
 " default will show icon by default if no icon is provided
 " default shows no icon by default
@@ -76,6 +79,8 @@ let g:nvim_tree_icons = {
     \   'ignored': "◌"
     \   },
     \ 'folder': {
+    \   'arrow_open': "",
+    \   'arrow_closed': "",
     \   'default': "",
     \   'open': "",
     \   'empty': "",

doc/nvim-tree-lua.txt

@@ -87,13 +87,17 @@ can disable icons per type:
     let g:nvim_tree_show_icons = {
 	\ 'git': 1,
 	\ 'folders': 1,
-	\ 'files': 1
+	\ 'files': 1,
+  \ 'folder_arrows': 1,
 	\}
 
 Can be one of `1` and `0` for each key. By default the tree will try
 to render the icons. The `files` key can only work if `nvim-web-devicons`
 is installed and in your |runtimepath|
 (https://github.com/kyazdani42/nvim-web-devicons)
+if folder is 1, you can also set `folder_arrows = 1` to show small arrows
+next to the folder icons but this will not work when you set 
+|g:nvim_tree_indent_markers| (because of UI conflict).
 
 |g:nvim_tree_highlight_opened_files|			        *g:nvim_tree_highlight_opened_files*
 
@@ -127,6 +131,8 @@ You can set icons for:
       \   'deleted':      "",
       \  },
       \ 'folder': {
+      \   'arrow_open':   "",
+      \   'arrow_closed': "",
       \   'default':      "",
       \   'open':         "",
       \   'empty':        "",

lua/nvim-tree/config.lua

@@ -1,7 +1,7 @@
 local M = {}
 
 function M.get_icon_state()
-  local show_icons = vim.g.nvim_tree_show_icons or { git = 1, folders = 1, files = 1 }
+  local show_icons = vim.g.nvim_tree_show_icons or { git = 1, folders = 1, files = 1, folder_arrows = 1 }
   local icons = {
     default = "",
     symlink = "",
@@ -15,6 +15,8 @@ function M.get_icon_state()
       ignored = "◌"
     },
     folder_icons = {
+      arrow_closed = "",
+      arrow_open = "",
       default = "",
       open = "",
       empty = "",
@@ -60,6 +62,7 @@ function M.get_icon_state()
     show_file_icon = show_icons.files == 1 and vim.g.nvim_web_devicons == 1,
     show_folder_icon = show_icons.folders == 1,
     show_git_icon = show_icons.git == 1,
+    show_folder_arrows = show_icons.folder_arrows == 1,
     icons = icons
   }
 end

lua/nvim-tree/renderer.lua

@@ -215,6 +215,16 @@ local get_padding = function(depth)
   return string.rep(' ', depth)
 end
 
+if icon_state.show_folder_icon and icon_state.show_folder_arrows then
+  get_padding = function(depth, _, _, node)
+    if node.entries then
+      local icon = icon_state.icons.folder_icons[node.open and 'arrow_open' or 'arrow_closed']
+      return string.rep(' ', depth - 2)..icon..' '
+    end
+    return string.rep(' ', depth)
+  end
+end
+
 if vim.g.nvim_tree_indent_markers == 1 then
   get_padding = function(depth, idx, tree, _, markers)
     local padding = ""
@@ -354,7 +364,9 @@ function M.draw(tree, reload)
     index = 0
     lines = {}
     hl = {}
-    update_draw_data(tree, 0, {})
+
+    local show_arrows = icon_state.show_folder_icon and icon_state.show_folder_arrows
+    update_draw_data(tree, show_arrows and 1 or 0, {})
   end
 
   api.nvim_buf_set_option(view.View.bufnr, 'modifiable', true)