Subject: Re: bug#38927: [patch] Backtrace printing in non-interactive mode doesn't use cl-prin1 etc.
From: Stefan Monnier <[email-masked]>
To: Stefan Kangas <[email-masked]>
Cc: [email-masked], Paul Pogonyshev <[email-masked]>
Date: Sat, 29 Feb 2020 09:07:08 -0500
List-Id: <debbugs-submit.debbugs.gnu.org>

> Do you have any comments on the below patch?  It seems to relate to a
> commit of yours, but has unfortunately not received any reply yet.

Hmm... looks like the bug tracker was kept out of the discussion.
This has been fixed already by 0223a1577c8999b8ea5eb35f39bc68360cbf5221

        Stefan

> Paul Pogonyshev <[email-masked]> writes:
>
>> tags
>>
>> Backtrace printing in batch mode ignores all customizations, at least:
>> - all `cl-print-object' overrides (`debugger-print-function');
>> - `print-level', `print-length' and friends;
>> - `debugger-batch-max-lines'.
>>
>> The reason is this commit:
>>
>> 7228488effa78dcb75284cb6d247b24804e0e7f5
>> Author:     Stefan Monnier <[email-masked]>
>> AuthorDate: 2018-04-02 00:23:20 -0400
>> [...]
>>
>> * lisp/emacs-lisp/debug.el (debug): Don't hang upon error in initial-frame.
>>
>> [...]
>> +   ((and (eq t (framep (selected-frame)))
>> +         (equal "initial_terminal" (terminal-name)))
>> +    ;; We're in the initial-frame (where `message' just outputs to stdout) so
>> +    ;; there's no tty or GUI frame to display the backtrace and interact with
>> +    ;; it: just dump a backtrace to stdout.
>> +    ;; This happens for example while handling an error in code from
>> +    ;; early-init.el with --debug-init.
>> +    (message "Error: %S" args)
>> [...]
>>
>> The commit added a "failsafe" mode for (quoting) "initial-frame (where
>> `message' just outputs to stdout) so there's no tty or GUI frame".
>> This failsafe mode is also erroneously triggered in batch mode. It was
>> never meant for it: you can see a couple of uses of `noninteractive'
>> in the next `cond' branch, but execution now never gets to it.
>>
>> Patch attached:
>> - don't use this "failsafe" mode when running non-interactively;
>> - repair for the latest changes in backtrace generation (apparently,
>> before the buffer was not read-only);
>> - repair adjustment for `debugger-batch-max-lines' which didn't make
>> any sense and didn't achieve what it claimed in the comment.
>>
>> Paul
>>
>> From 180f4a4f771696512af31ded93057713a5507147 Mon Sep 17 00:00:00 2001
>> From: Paul Pogonyshev <[email-masked]>
>> Date: Sat, 4 Jan 2020 22:47:24 +0100
>> Subject: [PATCH] Don't apply the special case to non-interactive mode in
>>  `debug'
>>
>> ---
>>  lisp/emacs-lisp/debug.el | 25 +++++++++++++------------
>>  1 file changed, 13 insertions(+), 12 deletions(-)
>>
>> diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
>> index 3df0ba4a65..b6c58b8c7b 100644
>> --- a/lisp/emacs-lisp/debug.el
>> +++ b/lisp/emacs-lisp/debug.el
>> @@ -172,7 +172,8 @@ debug
>>     (inhibit-redisplay
>>      ;; Don't really try to enter debugger within an eval from redisplay.
>>      debugger-value)
>> -   ((and (eq t (framep (selected-frame)))
>> +   ((and (not noninteractive)
>> +         (eq t (framep (selected-frame)))
>>           (equal "initial_terminal" (terminal-name)))
>>      ;; We're in the initial-frame (where `message' just outputs to stdout) so
>>      ;; there's no tty or GUI frame to display the backtrace and interact with
>> @@ -246,17 +247,17 @@ debug
>>  	        (when noninteractive
>>  		  ;; If the backtrace is long, save the beginning
>>  		  ;; and the end, but discard the middle.
>> -		  (when (> (count-lines (point-min) (point-max))
>> -			   debugger-batch-max-lines)
>> -		    (goto-char (point-min))
>> -		    (forward-line (/ 2 debugger-batch-max-lines))
>> -		    (let ((middlestart (point)))
>> -		      (goto-char (point-max))
>> -		      (forward-line (- (/ 2 debugger-batch-max-lines)
>> -				       debugger-batch-max-lines))
>> -		      (delete-region middlestart (point)))
>> -		    (insert "...\n"))
>> -		  (goto-char (point-min))
>> +                  (let ((inhibit-read-only t))
>> +		    (when (> (count-lines (point-min) (point-max))
>> +			     debugger-batch-max-lines)
>> +		      (goto-char (point-min))
>> +		      (forward-line (/ debugger-batch-max-lines 4))
>> +		      (let ((middlestart (point)))
>> +		        (goto-char (point-max))
>> +		        (forward-line (- (/ 2 debugger-batch-max-lines)
>> +				         debugger-batch-max-lines))
>> +		        (delete-region middlestart (point)))
>> +		      (insert "...\n")))
>>  		  (message "%s" (buffer-string))
>>  		  (kill-emacs -1)))
>>  	      (pop-to-buffer