Add :ResizeFixed command

plugin/commands.lua

@@ -205,3 +205,19 @@ end, { range = true })
 vim.api.nvim_create_user_command('DiagnosticToggle', function(_)
   vim.diagnostic.enable(not vim.diagnostic.is_enabled())
 end, {})
+
+-- :ResizeFixed acts like :resize but also fixes the window size so it stops
+-- automatically changing when other windows reflow. Respects the :vertical
+-- modifier, resizing and fixing the width instead of the height.
+vim.api.nvim_create_user_command('ResizeFixed', function(opts)
+  local cmd = { cmd = 'resize', mods = opts.smods }
+  if opts.args ~= '' then
+    cmd.args = { opts.args }
+  end
+  vim.cmd(cmd)
+  if opts.smods.vertical then
+    vim.wo.winfixwidth = true
+  else
+    vim.wo.winfixheight = true
+  end
+end, { nargs = '?' })