bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

[Visuwesh]

I have paredit-mode in emacs-lisp-mode-hook, and when the buffer has
mismatched parens [(check-paren)=nil], it signals an error.  This makes
`diff-add-log-current-entries' not add any of the entries.

For a simple reproducer,

    1. emacs -Q
   
    2. M-: (add-hook 'emacs-lisp-mode-hook (defun test () (error "test error")))

    3. Create a temporary git repo, commit an initial change by adding
       an elisp file.

    4. Add some more text.  C-x v v.

    5. C-c C-w.  Note "test error" in the echo-area.

I narrowed down the problem to `diff-add-log-current-entries' and I
*think* the problem is in goto-otherbuf function but when I added an
ignore-error around (funcall (buffer-local-value 'major-mode buf)), I
noticed no change.  :-/

I can work around my specific problem but it would be nice if this was
handled in a generic way.

In GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo version 1.16.0, Xaw scroll bars)
 of 2022-05-23 built on astatine
Repository revision: 9e088656c48b894f54bbc9265dbe37d2164b3d5f
Repository branch: imenu-xref
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: NixOS 21.11 (Porcupine)

Configured using:
 'configure --with-sqlite3 --with-x-toolkit=lucid --with-json
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 --without-libsystemd --with-modules CC=gcc PKG_CONFIG=pkg-config
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 CXX=g++'

Configured features:
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bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

[Lars Ingebrigtsen]

Visuwesh <visuweshm@gmail.com> writes:

> I have paredit-mode in emacs-lisp-mode-hook, and when the buffer has
> mismatched parens [(check-paren)=nil], it signals an error.  This makes
> `diff-add-log-current-entries' not add any of the entries.
>
> For a simple reproducer,
>
>     1. emacs -Q
>
>     2. M-: (add-hook 'emacs-lisp-mode-hook (defun test () (error "test error")))
>
>     3. Create a temporary git repo, commit an initial change by adding
>        an elisp file.
>
>     4. Add some more text.  C-x v v.
>
>     5. C-c C-w.  Note "test error" in the echo-area.
>
> I narrowed down the problem to `diff-add-log-current-entries' and I
> *think* the problem is in goto-otherbuf function but when I added an
> ignore-error around (funcall (buffer-local-value 'major-mode buf)), I
> noticed no change.  :-/

Isn't the problem here that paredit-mode signals an error when being
switched on?  Modes aren't supposed to do that.

For reference, here's the backtrace in the test case:

Debugger entered--Lisp error: (error "test error")
  signal(error ("test error"))
  error("test error")
  test()
  run-hooks(change-major-mode-after-body-hook prog-mode-hook lisp-data-mode-hook emacs-lisp-mode-hook)
  apply(run-hooks (change-major-mode-after-body-hook prog-mode-hook lisp-data-mode-hook emacs-lisp-mode-hook))
  run-mode-hooks(emacs-lisp-mode-hook)
  emacs-lisp-mode()
  #f(compiled-function () #<bytecode 0x1cc9cff9c51917ea>)()
  #f(compiled-function (&optional get-current) #<bytecode 0xba06c773444f87>)()
  diff-add-log-current-defuns()
  log-edit-generate-changelog-from-diff()
  funcall-interactively(log-edit-generate-changelog-from-diff)
  call-interactively(log-edit-generate-changelog-from-diff nil nil)
  command-execute(log-edit-generate-changelog-from-diff)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

[Visuwesh]

[சனி மே 28, 2022] Lars Ingebrigtsen wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> I have paredit-mode in emacs-lisp-mode-hook, and when the buffer has
>> mismatched parens [(check-paren)=nil], it signals an error.  This makes
>> `diff-add-log-current-entries' not add any of the entries.
>>
>> [...]
>> I narrowed down the problem to `diff-add-log-current-entries' and I
>> *think* the problem is in goto-otherbuf function but when I added an
>> ignore-error around (funcall (buffer-local-value 'major-mode buf)), I
>> noticed no change.  :-/
>
> Isn't the problem here that paredit-mode signals an error when being
> switched on?  Modes aren't supposed to do that.
>

If that is indeed the norm, then I can go complain elsewhere I guess.

> For reference, here's the backtrace in the test case:
> [...]

bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

[Lars Ingebrigtsen]

Visuwesh <visuweshm@gmail.com> writes:

> If that is indeed the norm, then I can go complain elsewhere I guess.

For the record, I'm unable to reproduce any problems if I say

(add-hook 'emacs-lisp-mode-hook 'paredit-mode)

and then otherwise follow your recipe.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

[Visuwesh]

[சனி மே 28, 2022] Lars Ingebrigtsen wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> If that is indeed the norm, then I can go complain elsewhere I guess.
>
> For the record, I'm unable to reproduce any problems if I say
>
> (add-hook 'emacs-lisp-mode-hook 'paredit-mode)
>
> and then otherwise follow your recipe.

That's because paredit-mode only signals an error if there's a paren or
quote mismatch---whenever `check-parens' errors.  paredit-mode signals
an error for the following chunk for me,

;;; Xref backend
;;;

;;;###autoload
(defun imenu-xref-backend ()
  (unless imenu--index-alist
    (imenu--make-index-alist))
  (when (and imenu--index-alist
             (not (progn (require 'etags) tags-table-files)))
    'imenu))

(cl-defmethod xref-backend-identifier-at-point ((_backend (eql 'imenu)))

I can work around the problem by doing,

    (setq paredit-override-check-parens-function #'always)

bug#55678: 29.0.50; C-c C-w and errors in major-mode-hook

[Lars Ingebrigtsen]

Visuwesh <visuweshm@gmail.com> writes:

> That's because paredit-mode only signals an error if there's a paren or
> quote mismatch---whenever `check-parens' errors.  paredit-mode signals
> an error for the following chunk for me,

Ah, yes of course.  And I think that's indeed a bug in paredit-mode --
a minor mode should not signal errors in this way, because it'll break
in exactly the scenarios like this.

I understand you've reported this to the paredit people, so I'm closing
this in the Emacs bug tracker.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no