Add lisp watchpoints

This allows calling a function whenever a symbol-value is changed.

* src/lisp.h (lisp_h_SYMBOL_TRAPPED_WRITE_P):
(SYMBOL_TRAPPED_WRITE_P): New function/macro.
(lisp_h_SYMBOL_CONSTANT_P): Check for SYMBOL_NOWRITE specifically.
(enum symbol_trapped_write): New enumeration.
(struct Lisp_Symbol): Rename field constant to trapped_write.
(make_symbol_constant): New function.

* src/data.c (Fadd_variable_watcher, Fremove_variable_watcher):
(set_symbol_trapped_write, restore_symbol_trapped_write):
(harmonize_variable_watchers, notify_variable_watchers): New functions.

* src/data.c (Fset_default): Call `notify_variable_watchers' for trapped
symbols.
(set_internal): Change bool argument BIND to 3-value enum and call
`notify_variable_watchers' for trapped symbols.

* src/data.c (syms_of_data):
* src/data.c (syms_of_data):
* src/font.c (syms_of_font):
* src/lread.c (intern_sym, init_obarray):
* src/buffer.c (syms_of_buffer): Use make_symbol_constant.

* src/alloc.c (init_symbol):
* src/bytecode.c (exec_byte_code): Use SYMBOL_TRAPPED_WRITE_P.
* src/data.c (Fmake_variable_buffer_local, Fmake_local_variable):
(Fmake_variable_frame_local):
* src/eval.c (Fdefvaralias, specbind): Refer to Lisp_Symbol's
trapped_write instead of constant.
(Ffuncall): Move subr calling code into separate function.
(funcall_subr): New function.

1 files changed, 48 insertions, 34 deletions

diff --git a/src/buffer.c b/src/buffer.c
index aa556b75bc6..6815aa7f7ed 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -984,40 +984,54 @@ reset_buffer_local_variables (struct buffer *b, bool permanent_too)
     bset_local_var_alist (b, Qnil);
   else
     {
-      Lisp_Object tmp, prop, last = Qnil;
+      Lisp_Object tmp, last = Qnil;
       for (tmp = BVAR (b, local_var_alist); CONSP (tmp); tmp = XCDR (tmp))
-        if (!NILP (prop = Fget (XCAR (XCAR (tmp)), Qpermanent_local)))
-          {
-            /* If permanent-local, keep it.  */
-            last = tmp;
-            if (EQ (prop, Qpermanent_local_hook))
-              {
-                /* This is a partially permanent hook variable.
-                   Preserve only the elements that want to be preserved.  */
-                Lisp_Object list, newlist;
-                list = XCDR (XCAR (tmp));
-                if (!CONSP (list))
-                  newlist = list;
-                else
-                  for (newlist = Qnil; CONSP (list); list = XCDR (list))
-                    {
-                      Lisp_Object elt = XCAR (list);
-                      /* Preserve element ELT if it's t,
-                         if it is a function with a `permanent-local-hook' property,
-                         or if it's not a symbol.  */
-                      if (! SYMBOLP (elt)
-                          || EQ (elt, Qt)
-                          || !NILP (Fget (elt, Qpermanent_local_hook)))
-                        newlist = Fcons (elt, newlist);
-                    }
-                XSETCDR (XCAR (tmp), Fnreverse (newlist));
-              }
-          }
-        /* Delete this local variable.  */
-        else if (NILP (last))
-          bset_local_var_alist (b, XCDR (tmp));
-        else
-          XSETCDR (last, XCDR (tmp));
+        {
+          Lisp_Object local_var = XCAR (XCAR (tmp));
+          Lisp_Object prop = Fget (local_var, Qpermanent_local);
+
+          if (!NILP (prop))
+            {
+              /* If permanent-local, keep it.  */
+              last = tmp;
+              if (EQ (prop, Qpermanent_local_hook))
+                {
+                  /* This is a partially permanent hook variable.
+                     Preserve only the elements that want to be preserved.  */
+                  Lisp_Object list, newlist;
+                  list = XCDR (XCAR (tmp));
+                  if (!CONSP (list))
+                    newlist = list;
+                  else
+                    for (newlist = Qnil; CONSP (list); list = XCDR (list))
+                      {
+                        Lisp_Object elt = XCAR (list);
+                        /* Preserve element ELT if it's t,
+                           if it is a function with a `permanent-local-hook' property,
+                           or if it's not a symbol.  */
+                        if (! SYMBOLP (elt)
+                            || EQ (elt, Qt)
+                            || !NILP (Fget (elt, Qpermanent_local_hook)))
+                          newlist = Fcons (elt, newlist);
+                      }
+                  newlist = Fnreverse (newlist);
+                  if (XSYMBOL (local_var)->trapped_write == SYMBOL_TRAPPED_WRITE)
+                    notify_variable_watchers (local_var, newlist,
+                                              Qmakunbound, Fcurrent_buffer ());
+                  XSETCDR (XCAR (tmp), newlist);
+                  continue; /* Don't do variable write trapping twice.  */
+                }
+            }
+          /* Delete this local variable.  */
+          else if (NILP (last))
+            bset_local_var_alist (b, XCDR (tmp));
+          else
+            XSETCDR (last, XCDR (tmp));
+
+          if (XSYMBOL (local_var)->trapped_write == SYMBOL_TRAPPED_WRITE)
+            notify_variable_watchers (local_var, Qnil,
+                                      Qmakunbound, Fcurrent_buffer ());
+        }
     }
 
   for (i = 0; i < last_per_buffer_idx; ++i)
@@ -5541,7 +5555,7 @@ file I/O and the behavior of various editing commands.
 This variable is buffer-local but you cannot set it directly;
 use the function `set-buffer-multibyte' to change a buffer's representation.
 See also Info node `(elisp)Text Representations'.  */);
-  XSYMBOL (intern_c_string ("enable-multibyte-characters"))->constant = 1;
+  make_symbol_constant (intern_c_string ("enable-multibyte-characters"));
 
   DEFVAR_PER_BUFFER ("buffer-file-coding-system",
                      &BVAR (current_buffer, buffer_file_coding_system), Qnil,