Renege on anonymous &rest (bug#50268, bug#50720)

Allowing &rest without a variable name following turned out not to be
very useful, and it never worked properly.  Disallow it.

* lisp/emacs-lisp/bytecomp.el (byte-compile-check-lambda-list):
* src/eval.c (funcall_lambda):
Signal error for &rest without variable name.
* doc/lispref/functions.texi (Argument List): Adjust manual.
* etc/NEWS (file): Announce.
* test/src/eval-tests.el (eval-tests--bugs-24912-and-24913):
Extend test, also checking with and without lexical binding.
(eval-tests-accept-empty-optional-rest): Reduce to...
(eval-tests-accept-empty-optional): ...this, again checking
with and without lexical binding.

1 files changed, 6 insertions, 3 deletions

diff --git a/src/eval.c b/src/eval.c
index 2bb7cfe6002..66d34808f82 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3245,6 +3245,7 @@ funcall_lambda (Lisp_Object fun, ptrdiff_t nargs,
     emacs_abort ();
 
   i = optional = rest = 0;
+  bool previous_rest = false;
   for (; CONSP (syms_left); syms_left = XCDR (syms_left))
     {
       maybe_quit ();
@@ -3255,13 +3256,14 @@ funcall_lambda (Lisp_Object fun, ptrdiff_t nargs,
 
       if (EQ (next, Qand_rest))
         {
-          if (rest)
+          if (rest || previous_rest)
             xsignal1 (Qinvalid_function, fun);
           rest = 1;
+          previous_rest = true;
         }
       else if (EQ (next, Qand_optional))
         {
-          if (optional || rest)
+          if (optional || rest || previous_rest)
             xsignal1 (Qinvalid_function, fun);
           optional = 1;
         }
@@ -3287,10 +3289,11 @@ funcall_lambda (Lisp_Object fun, ptrdiff_t nargs,
           else
             /* Dynamically bind NEXT.  */
             specbind (next, arg);
+          previous_rest = false;
         }
     }
 
-  if (!NILP (syms_left))
+  if (!NILP (syms_left) || previous_rest)
     xsignal1 (Qinvalid_function, fun);
   else if (i < nargs)
     xsignal2 (Qwrong_number_of_arguments, fun, make_fixnum (nargs));