fix(lua): report error in Lua Funcref callback properly (#35555)

runtime/doc/lsp.txt

@@ -162,7 +162,7 @@ order of increasing priority:
 
 1. Configuration defined for the `'*'` name.
 2. Configuration from the result of merging all tables returned by
-   `lsp/<name>.lua` files in 'runtimepath' for a server of name `name`.
+   `lsp/<config>.lua` files in 'runtimepath' for the config named `<config>`.
 3. Configurations defined anywhere else.
 
 Example: given the following configs... >lua
@@ -280,6 +280,12 @@ FAQ                                                     *lsp-faq*
      " (async = false is the default for format)
      autocmd BufWritePre *.rs lua vim.lsp.buf.format({ async = false })
 <
+
+- Q: How to avoid my own lsp/ folder being overridden?
+- A: Place your configs under "after/lsp/". Files in "after/lsp/" are loaded
+     after those in "nvim/lsp/", so your settings will take precedence over
+     the defaults provided by nvim-lspconfig. See also: |after-directory|
+
                                                         *lsp-vs-treesitter*
 - Q: How do LSP, Treesitter and Ctags compare?
 - A: LSP requires a client and language server. The language server uses

src/nvim/lua/executor.c

@@ -1496,7 +1496,7 @@ int typval_exec_lua_callable(LuaRef lua_cb, int argcount, typval_T *argvars, typ
   PUSH_ALL_TYPVALS(lstate, argvars, argcount, false);
 
   if (nlua_pcall(lstate, argcount, 1)) {
-    nlua_print(lstate);
+    nlua_error(lstate, _("Lua callback: %.*s"));
     return FCERR_OTHER;
   }
 

test/functional/lua/luaeval_spec.lua

@@ -16,6 +16,7 @@ local feed = n.feed
 local assert_alive = n.assert_alive
 local NIL = vim.NIL
 local eq = t.eq
+local matches = t.matches
 
 before_each(clear)
 
@@ -289,6 +290,8 @@ describe('luaeval()', function()
       return true
     ]]
     )
+    -- v:errmsg is set properly #35554
+    matches(': dead function\n', api.nvim_get_vvar('errmsg'))
   end)
 
   it('should handle passing functions around', function()