Re: debugger-toggle-locals

[Helmut Eller]

On Sun, Dec 01 2013, Stefan Monnier wrote:

>>       x: 9
>>       y: 114
>>       z: (9 . 114)
>
> Nitpick: I'd rather have "x=" instead of "x:" (for me, ":" means "has type").

Well, it's a debugger for Lisp not for ML.

>> +(defun debugger--backtrace-base ()
>> +  "Return the function name that marks the top of the backtrace.
>> +See `backtrace-frame'."
>> +  (cond ((eq 'debug--implement-debug-on-entry
>> +         (cadr (backtrace-frame 1 'debug)))
>> +     'debug--implement-debug-on-entry)
>> +    (t 'debug)))
>
> Please use it in debugger-eval-expression as well.

OK.

>> +(defun debugger--locals-visible-p ()
>> +  "Are the local variables of the current stack frame visible?"
>> +  (save-excursion
>> +    (move-to-column 2)
>> +    (get-text-property (point) 'debugger-locals-visible-p)))
>
> The text property shouldn't have a name that ends in `-p'; these names
> are for predicates (i.e. functions returning a boolean), not for
> variables or object fields, or symbol/text properties.

OK.

>> +  (dolist (s+v locals)
>> +    (let ((symbol (car s+v))
>> +      (value (cdr s+v))
>
> You can use (pcase-dolist (`(,symbol . ,value) locals) ...).

So many ` , . cause cancer of the semicolon.

>> + (cond ((string= (symbol-name symbol)
>> "internal-interpreter-environment")
>> +         (cond ((or (null value)
>> +                    (and (null (cdr value))
>> +                         (symbol (car value))))
>                               ^^^^^^
>                               should be `symbolp', right?
>
> `value' can also be of the form (a b t).
> I.e. (null (cdr value)) is false, but there are no values.
>
> But I tend to think that the handling of
> internal-interpreter-environment should be kept in the C code: this
> symbol should by and large not be exported to Elisp.

Done. Moved it to C.

Helmut

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index aa5b25b..ce2616c 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -494,9 +494,13 @@ removes itself from that hook."
       (forward-line 1)
       (while (progn
               (forward-char 2)
-              (if (= (following-char) ?\()
-                  (forward-sexp 1)
-                (forward-sexp 2))
+              (cond ((debugger--locals-visible-p)
+                     (goto-char (next-single-char-property-change
+                                 (point) 'locals-visible)))
+                    ((= (following-char) ?\()
+                     (forward-sexp 1))
+                    (t
+                     (forward-sexp 2)))
               (forward-line 1)
               (<= (point) opoint))
        (if (looking-at " *;;;")
@@ -541,6 +545,14 @@ Applies to the frame whose line point is on in the 
backtrace."
         (progn ,@body)
       (setq debugger-outer-match-data (match-data)))))
 
+(defun debugger--backtrace-base ()
+  "Return the function name that marks the top of the backtrace.
+See `backtrace-frame'."
+  (cond ((eq 'debug--implement-debug-on-entry
+            (cadr (backtrace-frame 1 'debug)))
+        'debug--implement-debug-on-entry)
+       (t 'debug)))
+
 (defun debugger-eval-expression (exp &optional nframe)
   "Eval an expression, in an environment like that outside the debugger.
 The environment used is the one when entering the activation frame at point."
@@ -549,15 +561,70 @@ The environment used is the one when entering the 
activation frame at point."
   (let ((nframe (or nframe
                     (condition-case nil (1+ (debugger-frame-number 'skip-base))
                       (error 0)))) ;; If on first line.
-         (base (if (eq 'debug--implement-debug-on-entry
-                      (cadr (backtrace-frame 1 'debug)))
-                  'debug--implement-debug-on-entry 'debug)))
+       (base (debugger--backtrace-base)))
     (debugger-env-macro
       (let ((val (backtrace-eval exp nframe base)))
         (prog1
             (prin1 val t)
           (let ((str (eval-expression-print-format val)))
             (if str (princ str t))))))))
+
+(defun debugger--locals-visible-p ()
+  "Are the local variables of the current stack frame visible?"
+  (save-excursion
+    (move-to-column 2)
+    (get-text-property (point) 'locals-visible)))
+
+(defun debugger--insert-locals (locals)
+  "Insert the local variables LOCALS at point."
+  (cond ((null locals)
+        (insert "\n    [no locals]"))
+       (t
+        (let ((print-escape-newlines t))
+          (dolist (s+v locals)
+            (let ((symbol (car s+v))
+                  (value (cdr s+v)))
+              (insert "\n    ")
+              (prin1 symbol (current-buffer))
+              (insert " = ")
+              (prin1 value (current-buffer))))))))
+
+(defun debugger--show-locals ()
+  "For the frame at point, insert locals and add text properties."
+  (let* ((nframe (1+ (debugger-frame-number 'skip-base)))
+        (base (debugger--backtrace-base))
+        (locals (backtrace-locals nframe base))
+        (inhibit-read-only t))
+    (save-excursion
+      (let ((start (progn
+                    (move-to-column 2)
+                    (point))))
+       (end-of-line)
+       (debugger--insert-locals locals)
+       (add-text-properties start (point) '(locals-visible t))))))
+
+(defun debugger--hide-locals ()
+  "Delete local variables and remove the text property."
+  (let* ((col (current-column))
+        (end (progn
+               (move-to-column 2)
+               (next-single-char-property-change (point) 'locals-visible)))
+        (start (previous-single-char-property-change end 'locals-visible))
+        (inhibit-read-only t))
+    (remove-text-properties start end '(locals-visible))
+    (goto-char start)
+    (end-of-line)
+    (delete-region (point) end)
+    (move-to-column col)))
+
+(defun debugger-toggle-locals ()
+  "Show or hide local variables of the current stack frame."
+  (interactive)
+  (cond ((debugger--locals-visible-p)
+        (debugger--hide-locals))
+       (t
+        (debugger--show-locals))))
+
 
 (defvar debugger-mode-map
   (let ((map (make-keymap))
@@ -575,6 +642,7 @@ The environment used is the one when entering the 
activation frame at point."
     (define-key map "h" 'describe-mode)
     (define-key map "q" 'top-level)
     (define-key map "e" 'debugger-eval-expression)
+    (define-key map "t" 'debugger-toggle-locals)
     (define-key map " " 'next-line)
     (define-key map "R" 'debugger-record-expression)
     (define-key map "\C-m" 'debug-help-follow)
diff --git a/src/eval.c b/src/eval.c
index d3fcec5..b538a40 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3576,6 +3576,66 @@ NFRAMES and BASE specify the activation frame to use, as 
in `backtrace-frame'.
      from the debugger.  */
   return unbind_to (count, eval_sub (exp));
 }
+
+DEFUN ("backtrace-locals", Fbacktrace_locals, Sbacktrace_locals, 1, 2, NULL,
+       doc: /* Return names and values of local variables of a stack frame.
+NFRAMES and BASE specify the activation frame to use, as in `backtrace-frame'.
+The result is an alist. */)
+  (Lisp_Object nframes, Lisp_Object base)
+{
+  union specbinding *frame = get_backtrace_frame (nframes, base);
+  union specbinding *prevframe =
+    get_backtrace_frame (make_number (XFASTINT (nframes) - 1), base);
+  ptrdiff_t distance = specpdl_ptr - frame;
+  Lisp_Object result = Qnil;
+  eassert (distance >= 0);
+
+  if (!backtrace_p (prevframe))
+    error ("Activation frame not found!");
+  if (!backtrace_p (frame))
+    error ("Activation frame not found!");
+
+  /* move values to specpdl */
+  backtrace_eval_unrewind (distance);
+
+  /* grab values */
+  {
+    union specbinding *tmp = prevframe;
+    for (; tmp > frame; tmp--)
+      {
+       switch (tmp->kind)
+         {
+         case SPECPDL_LET:
+         case SPECPDL_LET_DEFAULT:
+         case SPECPDL_LET_LOCAL:
+           {
+             Lisp_Object sym = specpdl_symbol (tmp);
+             Lisp_Object val = specpdl_old_value (tmp);
+             if (EQ (sym, Qinternal_interpreter_environment))
+               {
+                 Lisp_Object env = val;
+                 for (; CONSP (env); env = XCDR (env))
+                   {
+                     Lisp_Object binding = XCAR (env);
+                     if (CONSP (binding))
+                       result = Fcons (Fcons (XCAR (binding),
+                                              XCDR (binding)),
+                                       result);
+                   }
+               }
+             else
+               result = Fcons (Fcons (sym, val), result);
+           }
+         }
+      }
+  }
+
+  /* restore values from specpdl to original place */
+  backtrace_eval_unrewind (-distance);
+
+  return result;
+}
+
 
 void
 mark_specpdl (void)
@@ -3824,6 +3884,7 @@ alist of active lexical bindings.  */);
   defsubr (&Sbacktrace);
   defsubr (&Sbacktrace_frame);
   defsubr (&Sbacktrace_eval);
+  defsubr (&Sbacktrace_locals);
   defsubr (&Sspecial_variable_p);
   defsubr (&Sfunctionp);
 }