fix(plugin): dont allow `dir` changes when we already loaded files from the plugin's old dir. Show an error in this case. Fixes #993

lua/lazy/core/loader.lua

@@ -495,6 +495,7 @@ end
 function M.auto_load(modname, modpath)
   local plugin = Plugin.find(modpath)
   if plugin and modpath:find(plugin.dir, 1, true) == 1 then
+    plugin._.rtp_loaded = true
     -- don't load if we're loading specs or if the plugin is already loaded
     if not (Plugin.loading or plugin._.loaded) then
       if plugin.module == false then

lua/lazy/core/plugin.lua

@@ -459,10 +459,19 @@ function Spec:merge(old, new)
   end
 
   local new_dir = new._.dir or old._.dir or (new.name and (Config.options.root .. "/" .. new.name)) or nil
-  if new_dir ~= new.dir then
-    self:warn("Plugin `" .. new.name .. "` changed `dir`:\n- from: `" .. new.dir .. "`\n- to: `" .. new_dir .. "`")
+  if new_dir ~= old.dir then
+    local msg = "Plugin `" .. new.name .. "` changed `dir`:\n- from: `" .. old.dir .. "`\n- to: `" .. new_dir .. "`"
+    if new._.rtp_loaded or old._.rtp_loaded then
+      msg = msg
+        .. "\n\nThis plugin was already partially loaded, so we did not change it's `dir`.\nPlease fix your config."
+      self:error(msg)
+      new_dir = old.dir
+    else
+      self:warn(msg)
+    end
   end
   new.dir = new_dir
+  new._.rtp_loaded = new._.rtp_loaded or old._.rtp_loaded
 
   new._.super = old
   setmetatable(new, { __index = old })

lua/lazy/types.lua

@@ -19,6 +19,7 @@
 ---@field super? LazyPlugin
 ---@field module? string
 ---@field dir? string Explicit dir or dev set for this plugin
+---@field rtp_loaded? boolean
 
 ---@alias PluginOpts table|fun(self:LazyPlugin, opts:table):table?