Re: Making debugging possible on expressions executed from ielm

["Jarosław Rzeszótko" <jrzeszotko@gmail.com>]

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Stefan,

I did not know about condition-case-unless-debug, it indeed does make
debugging possible with a simpler change and without any side effects. I
attach the patch.

Cheers,
Jarosław Rzeszótko

On Sat, Jan 13, 2018 at 10:22 AM, Jarosław Rzeszótko <jrzeszotko@gmail.com>
wrote:

> I attach a patch for ielm.el that makes it possible to enter the debugger
> when executing expressions in ielm, and that makes ielm respect the
> debug-on-error and debug-on-exit flags.
>
> I guess that possibly the reason that was not originally done is that it
> is not obvious how to restore ielm to a usable state after the debugger has
> been entered. My patch makes use of the fact that unwind-protect unwind
> forms are still executed when user resumes execution from the debugger
> after an error.
>
> Without the patch, ielm wraps the evaluation of the expression given by
> the user in a condition case, and in case of an error, or exit, displays an
> appropriate message in its buffer, right under the evaluated expression,
> regardless of debug-on-error and debug-on-exit.
>
> With the patch, the message that ielm displays in its buffer will be a
> generic error message  regardless if there was an error in the evaluated
> form, or a quit. However:
>
> - if debug-on-error is t, emacs will enter the debugger and show a stack
> trace, just like with almost any other evaluation method. When the user
> continues the execution from the debugger, ielm will correctly resume
> execution
>
> - if debug-on-error is nil, emacs will display the specific error in the
> minibuffer anyway
>
> Similar things are true for debug-on-quit.
>
> I think this is an improvement over the current state of affairs. Of
> course ideally I would like to preserve the "nice" message in ielm buffer
> and make the improvements I made, but emacs does not seem to make it
> possible to do some handling of an error and then to re-raise it while
> preserving the original stack trace.
>
> Cheers,
> Jarosław Rzeszótko
>
>
>

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diff --git a/lisp/ielm.el b/lisp/ielm.el
index fb285e80f6..30d6515e69 100644
--- a/lisp/ielm.el
+++ b/lisp/ielm.el
@@ -354,7 +354,7 @@ nonempty, then flushes the buffer."
         (wbuf ielm-working-buffer)   ; current buffer after evaluation
         (pmark (ielm-pm)))
     (unless (ielm-is-whitespace-or-comment string)
-      (condition-case err
+      (condition-case-unless-debug err
           (let ((rout (read-from-string string)))
             (setq form (car rout)
                   pos (cdr rout)))
@@ -384,7 +384,7 @@ nonempty, then flushes the buffer."
                 (set-match-data ielm-match-data)
                 (save-excursion
                   (with-temp-buffer
-                    (condition-case err
+                    (condition-case-unless-debug err
                         (unwind-protect
                             ;; The next let form creates default
                             ;; bindings for *, ** and ***.  But
@@ -436,7 +436,7 @@ nonempty, then flushes the buffer."
 
       (goto-char pmark)
       (unless error-type
-        (condition-case nil
+        (condition-case-unless-debug nil
             ;; Self-referential objects cause loops in the printer, so
             ;; trap quits here. May as well do errors, too
             (unless for-effect
@@ -517,9 +517,6 @@ causes output to be directed to the ielm buffer.
 set to a different value during evaluation.  You can use (princ
 VALUE) or (pp VALUE) to write to the ielm buffer.
 
-Expressions evaluated by IELM are not subject to `debug-on-quit' or
-`debug-on-error'.
-
 The behavior of IELM may be customized with the following variables:
 * To stop beeping on error, set `ielm-noisy' to nil.
 * If you don't like the prompt, you can change it by setting `ielm-prompt'.