minor improvement to ':q' behaviour

prevents odd and slightly annoying situation when ':q' is used and
the file tree was open. if quitting the last non-file-tree window,
you then get left with a full-screen file tree instead of quitting
neovim. this fixes that.

nvim/lua/autocmds.lua

@@ -54,3 +54,44 @@ vim.api.nvim_create_autocmd('BufEnter', {
     end
   end,
 })
+
+-- Borrowed from nvim-tree wiki recipe:
+-- https://github.com/nvim-tree/nvim-tree.lua/wiki/Recipes#make-q-and-bd-work-as-if-tree-was-not-visible
+-- Make :bd and :q behave as usual when tree is visible
+vim.api.nvim_create_autocmd({ 'BufEnter', 'QuitPre' }, {
+  nested = false,
+  group = vim.api.nvim_create_augroup('gered-bufenter-quitpre-nvim-tree', { clear = true }),
+  callback = function(e)
+    local tree = require('nvim-tree.api').tree
+
+    -- Nothing to do if tree is not opened
+    if not tree.is_visible() then
+      return
+    end
+
+    -- How many focusable windows do we have? (excluding e.g. incline status window)
+    local winCount = 0
+    for _, winId in ipairs(vim.api.nvim_list_wins()) do
+      if vim.api.nvim_win_get_config(winId).focusable then
+        winCount = winCount + 1
+      end
+    end
+
+    -- We want to quit and only one window besides tree is left
+    if e.event == 'QuitPre' and winCount == 2 then
+      vim.api.nvim_cmd({ cmd = 'qall' }, {})
+    end
+
+    -- :bd was probably issued an only tree window is left
+    -- Behave as if tree was closed (see `:h :bd`)
+    if e.event == 'BufEnter' and winCount == 1 then
+      -- Required to avoid "Vim:E444: Cannot close last window"
+      vim.defer_fn(function()
+        -- close nvim-tree: will go to the last buffer used before closing
+        tree.toggle { find_file = true, focus = true }
+        -- re-open nivm-tree
+        tree.toggle { find_file = true, focus = false }
+      end, 10)
+    end
+  end,
+})