GNU bug report logs - #56643
29.0.50; Help-mode bookmarks not loading with native compilation

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#56643: closed (29.0.50; Help-mode bookmarks not loading with
 native compilation)
Date: Sat, 23 Jul 2022 09:58:02 +0000

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Your message dated Sat, 23 Jul 2022 12:57:49 +0300
with message-id <83leski21u.fsf <at> gnu.org>
and subject line Re: bug#56643: 29.0.50; Help-mode bookmarks not loading with native compilation
has caused the debbugs.gnu.org bug report #56643,
regarding 29.0.50; Help-mode bookmarks not loading with native compilation
to be marked as done.

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help-debbugs <at> gnu.org.)


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From: defun.foo <at> proton.me
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: 29.0.50; Help-mode bookmarks not loading with native compilation
Date: Tue, 19 Jul 2022 13:45:19 +0000

Overview:

With native compilation enabled, adding a bookmark in a help buffer seems to work normally for the duration of the Emacs session, but when Emacs is restarted an "Invalid read syntax: '#'" error is thrown and the entire bookmark list fails to load. This appears to be caused by a compiled lambda being serialized to the bookmark file in a way that is unreadable to the reader.

Emacs version:

29.0.5, compiled from latest master branch on 7-18-2022, and started with emacs -Q for both scenarios below.

Steps to reproduce:

1. Ensure that native compilation is enabled by running M-x native-comp-available-p
2. Run M-x describe-function {{any-function}} and move to the resulting *Help* buffer
3. Create a bookmark with C-x r m
4. Without quitting Emacs, kill the *Help* buffer, then run C-x r b to jump back to the bookmark (this works as expected)
5. Quit Emacs (C-x C-c), and restart
6. Attempt to jump to the same bookmark again (running C-x r b), and observe that the bookmark list fails to load and throws an "Invalid read syntax: '#'" error

Here is an example of a help bookmark as it was serialized to the bookmarks file (note the "help-fn" value):

("native-comp-bookmark"
 (position . 1)
 (last-modified 25301 49750 590832 312000)
 (help-fn . #<subr F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_9>)
 (help-args switch-to-buffer "*scratch*")
 (position . 1)
 (handler . help-bookmark-jump))

For comparison, I compiled Emacs without the native compilation flag (and verified that native-comp-available-p returned nil), and went through the same steps above, creating a new bookmark. Jumping back to the bookmark after restarting works as expected, and here is an example of that bookmark serialized without native comp:

("vanilla-bookmark"
 (position . 1)
 (last-modified 25301 49238 861856 736000)
 (help-fn .
          #[514 "\301
!\205\0\211\302!)\207"
                [describe-function-orig-buffer buffer-live-p describe-function]
                4 "\n\n(fn FUNCTION BUFFER)"])
 (help-args switch-to-buffer "*scratch*")
 (position . 1)
 (handler . help-bookmark-jump))

I did find an older similar bug (#24573 https://lists.gnu.org/archive/html/bug-gnu-emacs/2016-09/msg00971.html) which was causing the same error due to a buffer object being serialized. This was fixed by saving just the buffer name, but I'm not sure there's any comparable way to save a reference to a compiled lambda. Any advice would be much appreciated though!

[Message part 3 (message/rfc822, inline)]

From: Eli Zaretskii <eliz <at> gnu.org>
To: akrl <at> sdf.org, michael_heerdegen <at> web.de, defun.foo <at> proton.me
Cc: 56643-done <at> debbugs.gnu.org
Subject: Re: bug#56643: 29.0.50;
 Help-mode bookmarks not loading with native compilation
Date: Sat, 23 Jul 2022 12:57:49 +0300

> Cc: michael_heerdegen <at> web.de, defun.foo <at> proton.me, 56643 <at> debbugs.gnu.org
> Date: Fri, 22 Jul 2022 17:40:48 +0300
> From: Eli Zaretskii <eliz <at> gnu.org>
> 
> > > Thanks.  If Andrea confirms that this won't have any problems with
> > > native-compilation, I will install such changes on the release branch
> > > (since AFAIU this issue is a regression in Emacs 28).
> > 
> > I confirm it should just work.
> 
> Thanks, so I will make those changes on the release branch.

Done.

> > BTW, I mention this for other similar cases, another fix would be to add
> > (declare (speed -1)) to `describe-function'.
> 
> Thanks, good to know.  I guess we should document that in the ELisp
> manual.

Also done.

Closing.

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