[Neovim] Improve startup time

When I switched from [lazy.nvim] to `vim.pack`, I lost the ability to
lazily load plugins behind events of key bindings. I profiled the
behavior with `nvim --startuptime` and it seemed okay.

When I loaded up the changes on a computer with a much larger directory
with a much larger file history, I could tell that the startup was
noticeably slower. According to `nvim --startuptime`, it took 3.5
*seconds* to load.

The biggest offender was calculating the stats about plugins for my
dashboard. Removing this took off about 3 seconds by itself. While it
was nice to have, I honestly never paid any attention to it.

After this I began moving plugins behind events. I'd originally used
`vim.schedule` because I (wrongly) thought this would run the callback
_after_ startup. It turns out it runs the callback more or less after
the current event's callbacks are done. There are a few instances where
I took advantage of this by using `vim.schedule` instead of callback.
This all became enough of a pattern that I added a `load_on` helper.

Finally, because I was already well down the rabbit hole, I learned that
enabling spellcheck was taking about 10 milliseconds. I decided to drop
this, too, behind an event.

All of these changes together helped me reduce the 3.5 second startup
time to 45 milliseconds. I'm sure I'll discover things that don't work
quite right or don't load early enough, but we'll see how it goes as I
use it.

Author: dirn

.config/nvim/init.lua

@@ -1,6 +1,9 @@
 -- Set the leader first so that any plugins providing mappings will pick it up.
 vim.g.mapleader = [[ ]]
 
+-- Load plugin helpers.
+require("dirn.plugins")
+
 -- Initialize file types.
 require("dirn.filetypes")
 

.config/nvim/lua/dirn/dashboard.lua

@@ -92,51 +92,6 @@ local function header()
   }
 end
 
-local function plugins()
-  local opts = {
-    type = "text",
-    val = "You don't appear to be using any plugins.",
-    opts = { position = "center", hl = "Comment" },
-  }
-
-  vim.api.nvim_create_autocmd({ "User" }, {
-    pattern = { "AlphaReady" },
-    callback = function()
-      local ok, _ = pcall(require, "mason")
-      if ok then
-        vim.keymap.set("n", "M", function()
-          vim.cmd.Mason()
-        end, { silent = true, noremap = true, buffer = true })
-      end
-    end,
-  })
-
-  local all = vim.pack.get()
-  if #all > 0 then
-    local total = #all
-
-    local active = vim
-      .iter(all)
-      :filter(function(x)
-        return x.active
-      end)
-      :totable()
-
-    local loaded = "All"
-    if total ~= #active then
-      loaded = tostring(#active)
-    end
-
-    opts.val = "You are using "
-      .. total
-      .. " plugins. "
-      .. loaded
-      .. " of them are loaded."
-  end
-
-  return { opts }
-end
-
 local function recents()
   function recent(filename, label, shortcut)
     local action = "<cmd>e " .. filename .. "<cr>"
@@ -301,7 +256,6 @@ local sections = {
   footer = { type = "group", val = footer },
   greeting = { type = "group", val = greeting },
   header = { type = "group", val = header },
-  plugins = { type = "group", val = plugins },
   recents = { type = "group", val = recents },
   shortcuts = { type = "group", val = shortcuts },
 }
@@ -317,8 +271,6 @@ local config = {
     padding[1],
     sections.recents,
     padding[4],
-    sections.plugins,
-    padding[1],
     sections.footer,
   },
   opts = { margin = 3, redraw_on_resize = false },

.config/nvim/lua/dirn/plugins.lua

@@ -0,0 +1,11 @@
+---@param event string|string[]
+---@param callback fun(args: table)
+---@param opts? {schedule?: boolean}
+function load_on(event, callback, opts)
+  opts = opts or {}
+
+  vim.api.nvim_create_autocmd(event, {
+    once = true,
+    callback = opts.schedule and vim.schedule_wrap(callback) or callback,
+  })
+end

.config/nvim/lua/dirn/settings.lua

@@ -81,7 +81,12 @@ vim.opt.number = true
 vim.opt.title = true
 
 -- Use spell check.
-vim.opt.spell = true
+vim.api.nvim_create_autocmd({ "BufReadPost", "BufNewFile" }, {
+  once = true,
+  callback = function()
+    vim.opt.spell = true
+  end,
+})
 
 -- Make horizontal scrolling smoother.
 vim.opt.sidescroll = 1

.config/nvim/plugin/cmp.lua

@@ -1,4 +1,4 @@
-vim.schedule(function()
+load_on("InsertEnter", function()
   vim.pack.add({
     "https://github.com/hrsh7th/nvim-cmp",
 

.config/nvim/plugin/comment.lua

@@ -1,5 +1,7 @@
-vim.pack.add({
-  "https://github.com/numToStr/Comment.nvim",
-})
+load_on({ "BufReadPost", "BufNewFile" }, function()
+  vim.pack.add({
+    "https://github.com/numToStr/Comment.nvim",
+  })
 
-require("comment").setup()
+  require("comment").setup()
+end)

.config/nvim/plugin/committia.lua

@@ -1,3 +1,5 @@
+-- NOTE: If this plugin is deferred, it doesn't load in time to take over the commit
+-- message editor view.
 vim.pack.add({
   "https://github.com/rhysd/committia.vim",
 })

.config/nvim/plugin/conform.lua

@@ -1,4 +1,4 @@
-vim.schedule(function()
+load_on("BufWritePre", function()
   vim.pack.add({
     "https://github.com/stevearc/conform.nvim",
   })

.config/nvim/plugin/diminactive.lua

@@ -1,4 +1,4 @@
-vim.schedule(function()
+load_on("UIEnter", function()
   vim.pack.add({
     "https://github.com/blueyed/vim-diminactive",
   })

.config/nvim/plugin/exchange.lua

@@ -1,4 +1,4 @@
-vim.schedule(function()
+load_on({ "BufReadPost", "BufNewFile" }, function()
   vim.pack.add({
     "https://github.com/tommcdo/vim-exchange",
   })