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, 3 insertions, 3 deletions

diff --git a/src/lread.c b/src/lread.c
index eab9b8bea08..14f9393cc47 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3833,7 +3833,7 @@ intern_sym (Lisp_Object sym, Lisp_Object obarray, Lisp_Object index)
 
   if (SREF (SYMBOL_NAME (sym), 0) == ':' && EQ (obarray, initial_obarray))
     {
-      XSYMBOL (sym)->constant = 1;
+      make_symbol_constant (sym);
       XSYMBOL (sym)->redirect = SYMBOL_PLAINVAL;
       SET_SYMBOL_VAL (XSYMBOL (sym), sym);
     }
@@ -4120,12 +4120,12 @@ init_obarray (void)
 
   DEFSYM (Qnil, "nil");
   SET_SYMBOL_VAL (XSYMBOL (Qnil), Qnil);
-  XSYMBOL (Qnil)->constant = 1;
+  make_symbol_constant (Qnil);
   XSYMBOL (Qnil)->declared_special = true;
 
   DEFSYM (Qt, "t");
   SET_SYMBOL_VAL (XSYMBOL (Qt), Qt);
-  XSYMBOL (Qt)->constant = 1;
+  make_symbol_constant (Qt);
   XSYMBOL (Qt)->declared_special = true;
 
   /* Qt is correct even if CANNOT_DUMP.  loadup.el will set to nil at end.  */