Package: emacs;
Reported by: Alan Mackenzie <acm <at> muc.de>
Date: Wed, 15 Nov 2023 17:03:02 UTC
Severity: normal
Done: Alan Mackenzie <acm <at> muc.de>
Bug is archived. No further changes may be made.
Message #53 received at 67196 <at> debbugs.gnu.org (full text, mbox):
From: Alan Mackenzie <acm <at> muc.de> To: Eli Zaretskii <eliz <at> gnu.org> Cc: 67196 <at> debbugs.gnu.org, acm <at> muc.de, monnier <at> iro.umontreal.ca Subject: Re: bug#67196: M-: uses a wrong value of debug-on-error when it is nil. Date: Sat, 25 Nov 2023 12:40:03 +0000
Hello, Eli.
On Sat, Nov 25, 2023 at 13:15:15 +0200, Eli Zaretskii wrote:
> > Date: Sat, 25 Nov 2023 10:32:23 +0000
> > Cc: monnier <at> iro.umontreal.ca, 67196 <at> debbugs.gnu.org
> > From: Alan Mackenzie <acm <at> muc.de>
> > > How about not exposing the internal variable to Lisp at all?
> > That's a very good idea. It would need little more than a new C function
> > which would bind that variable then call eval. Maybe move
> > eval-expression-debug-on-error into eval.c, too.
> What I had in mind was a function exposed to Lisp that would set an
> internal variable not exposed to Lisp.
The would still require an unwind-protect somewhere. I've implemented
sub-eval-expression in eval.c. debug-from--eval-expression is no longer
visible from Lisp. Perhaps this is good enough.
> > > > For what it's worth, I lost about 10 hours of time trying to debug
> > > > a situation where I wasn't getting a backtrace, despite debug-on-error
> > > > being t. The problem was that d-o-e wasn't t at all, it was nil. M-:
> > > > had been lying.
> > > You never described that situation, AFAICT. I think you should, so
> > > that we could assess how grave the problem is, which is an important
> > > part of deciding whether the solution you propose is useful. I don't
> > > understand how could you NOT get a backtrace when debug-on-error is
> > > non-nil.
> > Sorry, I wasn't clear enough. During those 10 hours, I was under the
> > impression that debug-on-error was t, because M-: debug-on-error said so.
> > It actually was nil. That's why I submitted this bug report.
> So maybe instead of changing how this stuff works we should improve
> how debug-on-error's value is reported by M-: and other eval commands?
Yes, but that might be complicated, and won't help the user trying to
debug something which depends on debug-on-error, who is using M-: to try
to test it. I still say the bug is trying to make debug-on-error do too
much, more than it's capable of.
> Note that (AFAIU) your change doesn't just solve the problem you
> bumped into, it also changes the value of debug-on-error inside
> eval-expression etc., when eval-expression-debug-on-error's value is
> non-nil, but not t. I wonder what is the reason for that?
I don't see that in my current version of the patch (below). To test
this, I used the following:
(defun foo ()
(interactive)
(message "debug-on-error is %s" debug-on-error)
(message "eval-expression-debug-on-error is %s" eval-expression-debug-on-error)
(car 'foo))
, and called it with various settings of debug-on-error and
eval-expression-debug-on-error. In particular, with
(setq eval-expression-debug-on-error '(wrong-type-argument))
, I still see debug-on-error reported as nil.
diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 6d83aaf4d14..9d176c6c599 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -262,6 +262,13 @@ minibuffer-prompt-properties--setter
:value (nil)
(symbol :format "%v"))
(const :tag "always" t)))
+ (eval-expression-debug-on-error debug
+ (choice (const :tag "off")
+ (repeat :menu-tag "When"
+ :value (nil)
+ (symbol :format "%v"))
+ (const :tag "always" t))
+ "30.1")
(debug-ignored-errors debug (repeat (choice symbol regexp)))
(debug-on-quit debug boolean)
(debug-on-signal debug boolean)
diff --git a/lisp/simple.el b/lisp/simple.el
index 02c68912dba..f4c9873ceed 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -1980,13 +1980,6 @@ eval-expression-print-length
:type '(choice (const :tag "No Limit" nil) integer)
:version "21.1")
-(defcustom eval-expression-debug-on-error t
- "If non-nil set `debug-on-error' to t in `eval-expression'.
-If nil, don't change the value of `debug-on-error'."
- :group 'lisp
- :type 'boolean
- :version "21.1")
-
(defcustom eval-expression-print-maximum-character 127
"The largest integer that will be displayed as a character.
This affects printing by `eval-expression' (via
@@ -2120,34 +2113,18 @@ eval-expression
(cons (read--expression "Eval: ")
(eval-expression-get-print-arguments current-prefix-arg)))
- (let (result)
- (if (null eval-expression-debug-on-error)
- (setq result
- (values--store-value
- (eval (let ((lexical-binding t)) (macroexpand-all exp)) t)))
- (let ((old-value (make-symbol "t")) new-value)
- ;; Bind debug-on-error to something unique so that we can
- ;; detect when evalled code changes it.
- (let ((debug-on-error old-value))
- (setq result
- (values--store-value
- (eval (let ((lexical-binding t)) (macroexpand-all exp)) t)))
- (setq new-value debug-on-error))
- ;; If evalled code has changed the value of debug-on-error,
- ;; propagate that change to the global binding.
- (unless (eq old-value new-value)
- (setq debug-on-error new-value))))
-
- (let ((print-length (unless no-truncate eval-expression-print-length))
- (print-level (unless no-truncate eval-expression-print-level))
- (eval-expression-print-maximum-character char-print-limit)
- (deactivate-mark))
- (let ((out (if insert-value (current-buffer) t)))
- (prog1
- (prin1 result out)
- (let ((str (and char-print-limit
- (eval-expression-print-format result))))
- (when str (princ str out))))))))
+ (let* ((result (values--store-value
+ (sub-eval-expression (macroexpand-all exp))))
+ (print-length (unless no-truncate eval-expression-print-length))
+ (print-level (unless no-truncate eval-expression-print-level))
+ (eval-expression-print-maximum-character char-print-limit)
+ (deactivate-mark)
+ (out (if insert-value (current-buffer) t)))
+ (prog1
+ (prin1 result out)
+ (let ((str (and char-print-limit
+ (eval-expression-print-format result))))
+ (when str (princ str out))))))
(defun edit-and-eval-command (prompt command)
"Prompting with PROMPT, let user edit COMMAND and eval result.
diff --git a/src/eval.c b/src/eval.c
index 12e811ce264..eccabf3a091 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2033,7 +2033,8 @@ maybe_call_debugger (Lisp_Object conditions, Lisp_Object sig, Lisp_Object data)
/* Does user want to enter debugger for this kind of error? */
&& (signal_quit_p (sig)
? debug_on_quit
- : wants_debugger (Vdebug_on_error, conditions))
+ : (wants_debugger (Vdebug_from__eval_expression, conditions)
+ || wants_debugger (Vdebug_on_error, conditions)))
&& ! skip_debugger (conditions, combined_data)
/* See commentary on definition of
`internal-when-entered-debugger'. */
@@ -2383,6 +2384,19 @@ DEFUN ("eval", Feval, Seval, 1, 2, 0,
return unbind_to (count, eval_sub (form));
}
+DEFUN ("sub-eval-expression", Fsub_eval_expression, Ssub_eval_expression,
+ 1, 1, 0,
+ doc: /* Evaluate FORM and return its value.
+This function should be called only from `eval-expression'.
+It evaluates with `lexical-binding' non-nil, and handles
+`eval-expression-debug-on-error'. */)
+ (Lisp_Object form)
+{
+ specpdl_ref count = SPECPDL_INDEX ();
+ specbind (Qdebug_from__eval_expression, Veval_expression_debug_on_error);
+ return unbind_to (count, Feval (form, Qt));
+}
+
void
grow_specpdl_allocation (void)
{
@@ -4299,6 +4313,29 @@ syms_of_eval (void)
See also the variable `debug-on-quit' and `inhibit-debugger'. */);
Vdebug_on_error = Qnil;
+ DEFSYM (Qeval_expression_debug_on_error, "eval-expression-debug-on-error");
+ DEFVAR_LISP ("eval-expression-debug-on-error",
+ Veval_expression_debug_on_error,
+ doc: /* Non-nil means enter debugger on error on a call from `eval-expression'.
+Does not apply to errors handled by `condition-case' or those
+matched by `debug-ignored-errors'.
+Like `debug-on-error', this variable's value can also be a list,
+with the same meaning as for `debug-on-error'.
+
+A nil value for this variable will not prevent an entry to
+the debugger caused by other variables such as `debug-on-error'. */);
+ Veval_expression_debug_on_error = Qt;
+
+ DEFSYM (Qdebug_from__eval_expression, "debug-from--eval-expression");
+ DEFVAR_LISP ("debug-from--eval-expression", Vdebug_from__eval_expression,
+ doc: /* Non-nil means enter debugger if an error is signaled.
+This only applies in forms called by `eval-expression'. This variable
+has the same semantics as `debug-on-error'. It is an internal variable
+only. */);
+ Vdebug_from__eval_expression = Qnil;
+ /* debug-from--eval-expression should not be visible from Lisp. */
+ Funintern (Qdebug_from__eval_expression, Qnil);
+
DEFVAR_LISP ("debug-ignored-errors", Vdebug_ignored_errors,
doc: /* List of errors for which the debugger should not be called.
Each element may be a condition-name or a regexp that matches error messages.
@@ -4455,6 +4492,7 @@ syms_of_eval (void)
defsubr (&Sautoload);
defsubr (&Sautoload_do_load);
defsubr (&Seval);
+ defsubr (&Ssub_eval_expression);
defsubr (&Sapply);
defsubr (&Sfuncall);
defsubr (&Sfunc_arity);
--
Alan Mackenzie (Nuremberg, Germany).
GNU bug tracking system
Copyright (C) 1999 Darren O. Benham,
1997,2003 nCipher Corporation Ltd,
1994-97 Ian Jackson.