GNU bug report logs - #16368
24.3; freeze in cperl mode when editing a regexp

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Vincent Lefevre <vincent <at> vinc17.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3; freeze in cperl mode when editing a regexp
Date: Mon, 06 Jan 2014 02:28:29 +0100

Open a file in cperl mode containing the following line:

  /(\d{4})(?: +){2}/;

e.g.: "emacs -Q file" then M-x cperl-mode <RET>

Put the cursor over the second opening brace, and type <DEL>
several times to delete what is before "{2}". When one types
<DEL> at this point:

  /(\d{4})(?:{2}/;
             ^cursor

Emacs freezes. One can type C-g to interrupt.

One can also reproduce the bug by typing: /(\d{4})(?{2
Emacs freezes before the "2" appears.

This bug is also present with Emacs 23.

Bug also reported on:

  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=734325


In GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.8.6)
 of 2013-12-22 on brahms, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11405000
System Description:	Debian GNU/Linux unstable (sid)

Configured using:
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 '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib'
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 '--mandir=/usr/share/man' '--with-pop=yes'
 '--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3/site-lisp:/usr/share/emacs/site-lisp'
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 'LDFLAGS=-Wl,-z,relro' 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
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  value of $LC_TIME: en_DK
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Recent messages:
Loading /etc/emacs/site-start.d/50latex-cjk-common.el (source)...
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/usr/share/emacs24/site-lisp/flim/hmac-md5 hides /usr/share/emacs/24.3/lisp/net/hmac-md5
/usr/share/emacs24/site-lisp/flim/sasl-ntlm hides /usr/share/emacs/24.3/lisp/net/sasl-ntlm
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/usr/share/emacs24/site-lisp/html-helper-mode/tempo hides /usr/share/emacs/site-lisp/html-helper-mode/tempo
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Message #8 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: Vincent Lefevre <vincent <at> vinc17.net>
Cc: 16368 <at> debbugs.gnu.org
Subject: Re: bug#16368: 24.3; freeze in cperl mode when editing a regexp
Date: Sat, 21 Sep 2019 01:33:08 +0200

Vincent Lefevre <vincent <at> vinc17.net> writes:

> Open a file in cperl mode containing the following line:
>
>   /(\d{4})(?: +){2}/;
>
> e.g.: "emacs -Q file" then M-x cperl-mode <RET>
>
> Put the cursor over the second opening brace, and type <DEL>
> several times to delete what is before "{2}". When one types
> <DEL> at this point:
>
>   /(\d{4})(?:{2}/;
>              ^cursor
>
> Emacs freezes. One can type C-g to interrupt.

I can confirm this is still an issue in Emacs 26.1 and on the current
master branch.

Best regards,
Stefan Kangas

Message #15 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Harald Jörg <haj <at> posteo.de>
To: 16368 <at> debbugs.gnu.org
Subject: [PATCH] cperl-mode: don't freeze over a cool regexp
Date: Wed, 2 Sep 2020 22:06:40 +0200

[Message part 1 (text/plain, inline)]

That bug exists since 14 years, but only surfaces if the regexp has a
closing brace in the wrong place (two characters before an unfinished
group starts).  The reason is that `cperl-forward-group-in-re' failed
to report unbalanced parentheses: In the function, the error was too
narrowly localized and gets lost before returning.

Patch attached, including two test cases.
-- 
Cheers,
haj

[0001-2020-09-02-Harald-J-rg-haj-posteo.de.patch (text/x-patch, attachment)]

Message #18 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Harald Jörg <haj <at> posteo.de>, 16368 <at> debbugs.gnu.org
Subject: Re: bug#16368: [PATCH] cperl-mode: don't freeze over a cool regexp
Date: Wed, 2 Sep 2020 18:19:25 -0400

Harald Jörg <haj <at> posteo.de> writes:

> Patch attached, including two test cases.

Thanks for working on cperl-mode bugs.

Testing the original recipe with your patch it is already an improvement
in that it avoids the freeze.  But I see these messages:

  cperl-forward-group-in-re: error (scan-error Unbalanced parentheses 9 94)
  (scan-error Unbalanced parentheses 9 94)

Is that the expected and desired behavior?

---

Also, some minor nits:

> Subject: [PATCH] =?UTF-8?q?2020-09-02=20=20Harald=20J=C3=B6rg=20=20<haj <at> po?=
>  =?UTF-8?q?steo.de>?=

Better first line:

Fix freeze in cperl-mode when editing a regexp

>  * lisp/progmodes/cperl-mode.el (cperl-forward-group-in-re): Make
>  sure that an error is reported back to the caller (Bug#16368).
>
>  * test/lisp/progmodes/cperl-mode-tests.el (cperl-mode-test-bug-16368):
>  Tests for balanced (no error) and unbalanced (caught exception)
>  cases of `cperl-forward-group-in-re'.

Format these flush to the first column (no initial space).

> --- a/test/lisp/progmodes/cperl-mode-tests.el
> +++ b/test/lisp/progmodes/cperl-mode-tests.el

I see this:

    ELC      lisp/progmodes/cperl-mode-tests.elc

  In end of data:
  lisp/progmodes/cperl-mode-tests.el:73:1: Warning: the function
      `cperl-forward-group-in-re' is not known to be defined.

You should add this line to the top:

  (require 'cperl-mode)

Best regards,
Stefan Kangas

Message #23 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Harald Jörg <haj <at> posteo.de>
To: Stefan Kangas <stefankangas <at> gmail.com>, 16368 <at> debbugs.gnu.org
Subject: Re: bug#16368: [PATCH] cperl-mode: don't freeze over a cool regexp
Date: Thu, 3 Sep 2020 01:40:45 +0200

On 9/3/20 12:19 AM, Stefan Kangas wrote:
> Harald Jörg <haj <at> posteo.de> writes:
> 
>> Patch attached, including two test cases.
> 
> Thanks for working on cperl-mode bugs.
> 
> Testing the original recipe with your patch it is already an improvement
> in that it avoids the freeze.  But I see these messages:
> 
>   cperl-forward-group-in-re: error (scan-error Unbalanced parentheses 9 94)
>   (scan-error Unbalanced parentheses 9 94)
> 
> Is that the expected and desired behavior?

Yes, it is, sort of.  Maybe it should be fine-tuned.  At this point we
_have_ the situation of unbalanced parentheses, and cperl-mode rubs it
in for every character you type.

Just open a buffer in cperl-mode and start typing:

   $a =~ s/

At this point a message appears, with a different text when you open
a parentheses, and will haunt you until you get everything closed
properly.  Given that regexps can be messy and heavy with punctuation,
I'd say this is desired behavior.

I can only guess that the first part of the message (which starts with
"cperl-forward-group-in-re") was added out of frustration: The bug
prevented the second part of the message (without
"cperl-forward-group-in-re") from ever appearing.  Only this wasn't
fatal unless... there was this closing brace two characters before.
I'll check that, and prepare an updated patch if that's true.

> ---
> 
> Also, some minor nits:
> 
>> Subject: [PATCH] =?UTF-8?q?2020-09-02=20=20Harald=20J=C3=B6rg=20=20<haj <at> po?=
>>  =?UTF-8?q?steo.de>?=
> 
> Better first line:
> 
> Fix freeze in cperl-mode when editing a regexp
> 
>>  * lisp/progmodes/cperl-mode.el (cperl-forward-group-in-re): Make
>>  sure that an error is reported back to the caller (Bug#16368).
>>
>>  * test/lisp/progmodes/cperl-mode-tests.el (cperl-mode-test-bug-16368):
>>  Tests for balanced (no error) and unbalanced (caught exception)
>>  cases of `cperl-forward-group-in-re'.
> 
> Format these flush to the first column (no initial space).

No problem, I'll do so.  I thought I was supposed to create the commit
messages with C-x 4 a, but probably I misunderstood and should have
post-processed that text in the first place.

>> --- a/test/lisp/progmodes/cperl-mode-tests.el
>> +++ b/test/lisp/progmodes/cperl-mode-tests.el
> 
> I see this:
> 
>     ELC      lisp/progmodes/cperl-mode-tests.elc
> 
>   In end of data:
>   lisp/progmodes/cperl-mode-tests.el:73:1: Warning: the function
>       `cperl-forward-group-in-re' is not known to be defined.
> 
> You should add this line to the top:
> 
>   (require 'cperl-mode)

Hm. That should rather be _moving_ that line to the top?  The line is
there, in the test which calls this function.  For me this seemed to
be enough to avoid that message when byte-compiling.  But of course,
moving the line to the top is fine, probably more tests will follow
to exercise functions which aren't autoloaded.

Give me a few hours for a nap: It's past midnight here :)
-- 
Cheers,
haj

Message #26 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Harald Jörg <haj <at> posteo.de>, 16368 <at> debbugs.gnu.org
Subject: Re: bug#16368: [PATCH] cperl-mode: don't freeze over a cool regexp
Date: Thu, 3 Sep 2020 02:58:40 -0700

Harald Jörg <haj <at> posteo.de> writes:

> I'd say this is desired behavior.

OK, thanks.  Your explanation sounds good to me.

> I can only guess that the first part of the message (which starts with
> "cperl-forward-group-in-re") was added out of frustration: The bug
> prevented the second part of the message (without
> "cperl-forward-group-in-re") from ever appearing.  Only this wasn't
> fatal unless... there was this closing brace two characters before.
> I'll check that, and prepare an updated patch if that's true.

Sounds good.

> No problem, I'll do so.  I thought I was supposed to create the commit
> messages with C-x 4 a, but probably I misunderstood and should have
> post-processed that text in the first place.

I always use C-x 4 a, and then delete the spacing to the left.

> Hm. That should rather be _moving_ that line to the top?

Ah, right.  Yup, that sounds good.

Message #29 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Harald Jörg <haj <at> posteo.de>
To: Stefan Kangas <stefankangas <at> gmail.com>, 16368 <at> debbugs.gnu.org
Subject: Re: bug#16368: [PATCH] cperl-mode: don't freeze over a cool regexp
Date: Thu, 3 Sep 2020 22:27:12 +0200

[Message part 1 (text/plain, inline)]

On 9/3/20 11:58 AM, Stefan Kangas wrote:
> Harald Jörg <haj <at> posteo.de> writes:
>
>> I'd say this is desired behavior.
>
> OK, thanks.  Your explanation sounds good to me.

It wasn't quite accurate, though.  My explanation assumed that the
regex as a whole wasn't terminated, but in fact it was.  In fact, the
message comes from the fact that (?{...}) introduces a block of code
into the regexp.  So, by removing the colon from (?:{...}), the
semantics changed from "just another shy group" to "code", and for
code cperl-mode applies stricter rules than for the contents of a
capture group.

I'd still say the message is ok.

>> I can only guess that the first part of the message (which starts with
>> "cperl-forward-group-in-re") was added out of frustration: The bug
>> prevented the second part of the message (without
>> "cperl-forward-group-in-re") from ever appearing.  Only this wasn't
>> fatal unless... there was this closing brace two characters before.
>> I'll check that, and prepare an updated patch if that's true.
>
> Sounds good.

...And done.  Now you get only one message, without the unnecessary
"cperl-forward-group-in-re" prefix.

>> No problem, I'll do so.  I thought I was supposed to create the commit
>> messages with C-x 4 a, but probably I misunderstood and should have
>> post-processed that text in the first place.
>
> I always use C-x 4 a, and then delete the spacing to the left.

Ok, adapted.  I have also used your recommendation for the commit
summary.

>> Hm. That should rather be _moving_ that line to the top?
>
> Ah, right.  Yup, that sounds good.

When I did this, I stumbled over the purpose of Stefan Monniers change
to the tests - this has been taken to emacs-devel.  For now, moving
the line to the top and skipping the test if called in a perl-mode
environment, should do the trick.

Patch, mark2, is attached!
-- 
Cheers,
haj

[0001-Fix-freeze-in-cperl-mode-when-editing-a-regexp.patch (text/x-patch, attachment)]

Message #32 received at 16368 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Harald Jörg <haj <at> posteo.de>, 16368 <at> debbugs.gnu.org
Subject: Re: bug#16368: [PATCH] cperl-mode: don't freeze over a cool regexp
Date: Thu, 3 Sep 2020 21:12:29 +0000

close 16368 28.1
thanks

Harald Jörg <haj <at> posteo.de> writes:

> Patch, mark2, is attached!

LGTM, tested and works as far as I can tell.

Pushed to master as commit 7921b5db10.

Thanks!

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