add autocmds

config/programs/vim/configuration.nix

@@ -89,6 +89,7 @@ in {
 
     extraLuaModules = [
       "config.undodir"
+      "custom_autocmd"
     ];
 
     vim.g.isDesktop = config.isDesktop;

config/programs/vim/modules/lua/custom_autocmd.lua

@@ -0,0 +1,66 @@
+local fn = vim.fn
+local api = vim.api
+
+local utils = require("utils")
+
+-- Display a message when the current file is not in utf-8 format.
+-- Note that we need to use `unsilent` command here because of this issue:
+-- https://github.com/vim/vim/issues/4379
+api.nvim_create_autocmd({ "BufRead" }, {
+    pattern = "*",
+    group = api.nvim_create_augroup("non_utf8_file", { clear = true }),
+    callback = function()
+        if vim.bo.fileencoding ~= "utf-8" then
+            vim.notify("File not in UTF-8 format!", vim.log.levels.WARN, { title = "nvim-config" })
+        end
+    end,
+})
+
+-- highlight yanked region, see `:h lua-highlight`
+api.nvim_create_autocmd({ "TextYankPost" }, {
+    pattern = "*",
+    group = api.nvim_create_augroup("highlight_yank", { clear = true }),
+    callback = function()
+        vim.highlight.on_yank { higroup = "YankColor", timeout = 300 }
+    end,
+})
+
+-- Auto-create dir when saving a file, in case some intermediate directory does not exist
+api.nvim_create_autocmd({ "BufWritePre" }, {
+    pattern = "*",
+    group = api.nvim_create_augroup("auto_create_dir", { clear = true }),
+    callback = function(ctx)
+        local dir = fn.fnamemodify(ctx.file, ":p:h")
+        utils.may_create_dir(dir)
+    end,
+})
+
+-- Automatically reload the file if it is changed outside of Nvim, see https://unix.stackexchange.com/a/383044/221410.
+-- It seems that `checktime` does not work in command line. We need to check if we are in command
+-- line before executing this command, see also https://vi.stackexchange.com/a/20397/15292 .
+api.nvim_create_augroup("auto_read", { clear = true })
+
+api.nvim_create_autocmd({ "FileChangedShellPost" }, {
+    pattern = "*",
+    group = "auto_read",
+    callback = function()
+        vim.notify("File changed on disk. Buffer reloaded!", vim.log.levels.WARN, { title = "nvim-config" })
+    end,
+})
+
+api.nvim_create_autocmd({ "FocusGained", "CursorHold" }, {
+    pattern = "*",
+    group = "auto_read",
+    callback = function()
+        if fn.getcmdwintype() == "" then
+            vim.cmd("checktime")
+        end
+    end,
+})
+
+-- Resize all windows when we resize the terminal
+api.nvim_create_autocmd("VimResized", {
+    group = api.nvim_create_augroup("win_autoresize", { clear = true }),
+    desc = "autoresize windows on resizing operation",
+    command = "wincmd =",
+})

config/programs/vim/modules/lua/utils.lua

@@ -0,0 +1,59 @@
+local fn = vim.fn
+
+local M = {}
+
+function M.executable(name)
+    if fn.executable(name) > 0 then
+        return true
+    end
+
+    return false
+end
+
+--- check whether a feature exists in Nvim
+--- @feat: string
+---     the feature name, like `nvim-0.7` or `unix`.
+--- return: bool
+M.has = function(feat)
+    if fn.has(feat) == 1 then
+        return true
+    end
+
+    return false
+end
+
+--- Create a dir if it does not exist
+function M.may_create_dir(dir)
+    local res = fn.isdirectory(dir)
+
+    if res == 0 then
+        fn.mkdir(dir, "p")
+    end
+end
+
+--- Generate random integers in the range [Low, High], inclusive,
+--- adapted from https://stackoverflow.com/a/12739441/6064933
+--- @low: the lower value for this range
+--- @high: the upper value for this range
+function M.rand_int(low, high)
+    -- Use lua to generate random int, see also: https://stackoverflow.com/a/20157671/6064933
+    math.randomseed(os.time())
+
+    return math.random(low, high)
+end
+
+--- Select a random element from a sequence/list.
+--- @seq: the sequence to choose an element
+function M.rand_element(seq)
+    local idx = M.rand_int(1, #seq)
+
+    return seq[idx]
+end
+
+function M.add_pack(name)
+    local status, error = pcall(vim.cmd, "packadd " .. name)
+
+    return status
+end
+
+return M