Fix subtle errors with let-binding of localized variables

* src/eval.c (do_specbind): Don't require a "symbol" that is
actually a cons cell, in order to call set-default, as there are
no longer such bindings.  This makes do_specbind work like the
pre-concurrency implementation in specbind for bindings of
forwarded symbols.  Use specpdl_kind to access the type of the
binding.
(specpdl_kind): New function.

1 files changed, 14 insertions, 16 deletions

diff --git a/src/eval.c b/src/eval.c
index 9657f51aadc..5383d7c3b1b 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -102,6 +102,13 @@ specpdl_symbol (union specbinding *pdl)
   return pdl->let.symbol;
 }
 
+static enum specbind_tag
+specpdl_kind (union specbinding *pdl)
+{
+  eassert (pdl->kind >= SPECPDL_LET);
+  return pdl->let.kind;
+}
+
 static Lisp_Object
 specpdl_old_value (union specbinding *pdl)
 {
@@ -3170,23 +3177,15 @@ do_specbind (struct Lisp_Symbol *sym, union specbinding *bind,
         set_internal (specpdl_symbol (bind), value, Qnil, SET_INTERNAL_BIND);
       break;
 
-    case SYMBOL_LOCALIZED:
     case SYMBOL_FORWARDED:
-      if ((sym->redirect == SYMBOL_LOCALIZED
-           || BUFFER_OBJFWDP (SYMBOL_FWD (sym)))
-          && CONSP (specpdl_symbol (bind)))
+      if (BUFFER_OBJFWDP (SYMBOL_FWD (sym))
+          && specpdl_kind (bind) == SPECPDL_LET_DEFAULT)
         {
-          Lisp_Object where;
-
-          where = XCAR (XCDR (specpdl_symbol (bind)));
-          if (NILP (where)
-              && sym->redirect == SYMBOL_FORWARDED)
-            {
-              Fset_default (XCAR (specpdl_symbol (bind)), value);
-              return;
-            }
+          Fset_default (specpdl_symbol (bind), value);
+          return;
         }
-
+      /* FALLTHROUGH */
+    case SYMBOL_LOCALIZED:
       set_internal (specpdl_symbol (bind), value, Qnil, SET_INTERNAL_BIND);
       break;
 
@@ -3361,8 +3360,7 @@ do_one_unbind (union specbinding *this_binding, bool unwinding)
       break;
     case SPECPDL_LET:
       { /* If variable has a trivial value (no forwarding), and isn't
-           trapped we can just set it.  No need to check for constant
-           symbols here, since that was already done by specbind.  */
+           trapped, we can just set it.  */
         Lisp_Object sym = specpdl_symbol (this_binding);
         if (SYMBOLP (sym) && XSYMBOL (sym)->redirect == SYMBOL_PLAINVAL)
           {