3 files changed, 33 insertions, 11 deletions

diff --git a/etc/NEWS b/etc/NEWS
index b2a213c8fa2..a60962cf1f4 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -221,6 +221,7 @@ Secret Service API requires D-Bus for communication.
 
 * Lisp changes in Emacs 24.1
 
+** frame-local variables cannot be let-bound any more.
 ** prog-mode is a new major-mode meant to be the parent of programming mode.
 ** define-minor-mode accepts a new keyword :variable.
 
diff --git a/src/ChangeLog b/src/ChangeLog
index 14311049a17..f258174625a 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2010-05-14  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * eval.c (specbind): Remove left-over duplicate test.
+        Disallow let-binding frame-local vars.  Add comment.
+
 2010-05-14  Eli Zaretskii  <eliz@gnu.org>
 
         Make the cache of bidi iterator states dynamically allocated.
@@ -5,7 +10,7 @@
         (bidi_init_it): Call it.
         (bidi_cache_iterator_state): Enlarge the cache if needed.
 
-        * bidi.c (bidi_move_to_visually_next): Renamed from
+        * bidi.c (bidi_move_to_visually_next): Rename from
         bidi_get_next_char_visually.  All callers changed.
 
 2010-05-14  Kenichi Handa  <handa@m17n.org>
@@ -18,8 +23,8 @@
         Set CMP_IT->reversed_p.
         (composition_update_it): Pay attention to CMP_IT->reversed_p.
 
-        * xdisp.c (set_iterator_to_next): Call
-        composition_compute_stop_pos with negative ENDPOS if we are
+        * xdisp.c (set_iterator_to_next):
+        Call composition_compute_stop_pos with negative ENDPOS if we are
         scanning backward.  Call composition_compute_stop_pos if scan
         direction is changed.
         (next_element_from_buffer): Call composition_compute_stop_pos with
diff --git a/src/eval.c b/src/eval.c
index 2a0330acc38..199c4705736 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3308,6 +3308,21 @@ grow_specpdl ()
   specpdl_ptr = specpdl + count;
 }
 
+/* specpdl_ptr->symbol is a field which describes which variable is
+   let-bound, so it can be properly undone when we unbind_to.
+   It can have the following two shapes:
+   - SYMBOL : if it's a plain symbol, it means that we have let-bound
+     a symbol that is not buffer-local (at least at the time
+     the let binding started).  Note also that it should not be
+     aliased (i.e. when let-binding V1 that's aliased to V2, we want
+     to record V2 here).
+   - (SYMBOL WHERE . BUFFER) : this means that it is a let-binding for
+     variable SYMBOL which can be buffer-local.  WHERE tells us
+     which buffer is affected (or nil if the let-binding affects the
+     global value of the variable) and BUFFER tells us which buffer was
+     current (i.e. if WHERE is non-nil, then BUFFER==WHERE, otherwise
+     BUFFER did not yet have a buffer-local value).  */
+
 void
 specbind (symbol, value)
      Lisp_Object symbol, value;
@@ -3339,7 +3354,10 @@ specbind (symbol, value)
             set_internal (symbol, value, Qnil, 1);
           break;
         }
-    case SYMBOL_LOCALIZED: case SYMBOL_FORWARDED:
+    case SYMBOL_LOCALIZED:
+      if (SYMBOL_BLV (sym)->frame_local)
+        error ("Frame-local vars cannot be let-bound");
+    case SYMBOL_FORWARDED:
       {
         Lisp_Object ovalue = find_symbol_value (symbol);
         specpdl_ptr->func = 0;
@@ -3376,6 +3394,7 @@ specbind (symbol, value)
             /* FIXME: The third value `current_buffer' is only used in
                let_shadows_buffer_binding_p which is itself only used
                in set_internal for local_if_set.  */
+            eassert (NILP (where) || EQ (where, cur_buf));
             specpdl_ptr->symbol = Fcons (symbol, Fcons (where, cur_buf));
 
             /* If SYMBOL is a per-buffer variable which doesn't have a
@@ -3460,13 +3479,10 @@ unbind_to (count, value)
             Fset_default (symbol, this_binding.old_value);
           /* If `where' is non-nil, reset the value in the appropriate
              local binding, but only if that binding still exists.  */
-          else if (BUFFERP (where))
-            {
-              if (BUFFERP (where)
-                  ? !NILP (Flocal_variable_p (symbol, where))
-                  : !NILP (Fassq (symbol, XFRAME (where)->param_alist)))
-                set_internal (symbol, this_binding.old_value, where, 1);
-            }
+          else if (BUFFERP (where)
+                   ? !NILP (Flocal_variable_p (symbol, where))
+                   : !NILP (Fassq (symbol, XFRAME (where)->param_alist)))
+            set_internal (symbol, this_binding.old_value, where, 1);
         }
       /* If variable has a trivial value (no forwarding), we can
          just set it.  No need to check for constant symbols here,