bug#62794: 28.2; jit-lock-function enters busy loop when open """ near top of large Python program

[Nick Urbanik]

Dear Eli,

Thank you very much for your helpful and rapid response.  Emacs has
never let me down in daily use from 1993 till this problem came up.

On 12/04/23 18:39 +0300, Eli Zaretskii wrote:
> > Date: Wed, 12 Apr 2023 17:05:13 +1000
> > From: Nick Urbanik <nicku@nicku.org>
> >
> >
> >
> > 1. Start emacs with emacs -Q
> > 2. Read in a large python file (3100 lines long, more than 10,000
> >     characters)
>
> Thanks.
>
> Please post such a file, or a URL where it could be downloaded.  I
> couldn't easily find such a large file on my system.

It turns out that it is not the size, but some pathological
arrangement of the code.  I have provided a much smaller sample here
that I can reproduce the problem with by:

1. Move the cursor to below the from elesewhere import ... line.
2. Press Enter
3. Type:
def function():
    """

4. At this point, CPU usage goes to 100%, I cannot type anything else
into the buffer, but I can send a USR2 signal to end the 100% CPU
usage, but the buffer has only partial syntax colouring.
> > 3. Near the top, type the following:
> >
> > def function():
> >     """
> >
> > 4. No further input is accepted.
> > 5. CPU usage is 100% as shown in /usr/bin/top
> > 6. type kill -USR2 {process_id_of_emacs-Q}
> >     and the emacs window closes.
> > 7. From my emacs started without '-Q', when I type
> >     killall -USR2 emacs
> >     I see:
> > Debugger entered--entering a function:
>
> I suspect this is already fixed in Emacs 29, but I cannot verify
> without a file that reproduces the problem in Emacs 28.

I will build an RPM package of emacs 29 and test that.
--
Nick Urbanik             http://nicku.org           nicku@nicku.org
GPG: 7FFA CDC7 5A77 0558 DC7A 790A 16DF EC5B BB9D 2C24 ID: BB9D2C24

head-a.py
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