feat(nvim): add DiffSaved user command

dots/.config/nvim/lua/core/cmds.lua

@@ -1,6 +1,32 @@
 local M = {}
 M.setup = function()
     vim.api.nvim_create_user_command("StripTrailSpace", "%s/\\s\\+$//e", {})
+    vim.api.nvim_create_user_command("DiffSaved", function()
+        -- Thanks to sindrets: https://github.com/sindrets/dotfiles/blob/1990282dba25aaf49897f0fc70ebb50f424fc9c4/.config/nvim/lua/user/lib.lua#L175
+        -- Minor alterations by me
+        local buf_ft = vim.api.nvim_get_option_value("filetype", { scope = "local" })
+        local buf_name = vim.api.nvim_buf_get_name(0)
+        vim.cmd("tab split | diffthis")
+        vim.cmd("aboveleft vnew | r # | normal! 1Gdd")
+        vim.cmd.diffthis()
+        local opts = {
+            buftype = "nowrite",
+            bufhidden = "wipe",
+            swapfile = false,
+            readonly = true,
+            winbar = vim.opt.winbar:get()
+        }
+        for option, value in pairs(opts) do
+            vim.api.nvim_set_option_value(option, value, { scope = "local" })
+        end
+        if buf_name then
+            pcall(vim.api.nvim_buf_set_name, 0, (vim.fn.fnamemodify(buf_name, ":t") or buf_name) .. " [OLD]")
+        end
+        if buf_ft then
+            vim.opt_local.filetype = buf_ft
+        end
+        vim.cmd.wincmd("l")
+    end, {})
 end
 
 return M