bug#74738: 31.0.50; Freezes in Python-mode on some Python file when searching or scrolling

[rehan malak <rehan.malak@gmail.com>]

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thanks kobarity, with your patch, I confirm that :
- I can open gef.py and scroll
- I get the correct font-lock-string-face in the f-string after a "#" in
the format

On Wed, Dec 11, 2024 at 3:24 PM kobarity <kobarity@gmail.com> wrote:

> rehan malak wrote:
> > Deleting all the "#" in the f-string of the gef.py file removes the
> problem on my side.
> >  sed -i -e 's/#0{align/0{align/g' gef.py
> >  sed -i -e 's/#0{width/0{width/g' gef.py
> >  sed -i -e 's/#07x}/07x}/g' gef.py
> >  sed -i -e 's/#06x}/06x}/g' gef.py
> >  sed -i -e 's/#04x}/04x}/g' gef.py
> >  sed -i -e 's/#4x}/4x}/g' gef.py
> >  sed -i -e 's/#8x}/8x}/g' gef.py
> >  sed -i -e 's/#10x}/10x}/g' gef.py
> >  sed -i -e 's/#x}/x}/g' gef.py
> >
> > Your smaller example Eli also contains a f-string with the "#".
> >
> > This python f-string format specifier is described here:
> >
> https://docs.python.org/3/library/string.html#format-specification-mini-language
> >
> > Is this format specifier supported from the beginning ?
> >
> > For example :
> >
> > value = 0xab
> > print(f"{value:x} is a value")
> >
> > => color syntax : is a value    has the color defined by
> font-lock-string-face
> >
> > while
> >
> > value = 0xab
> > print(f"{value:#x} is a value")
> >
> > => color are messed up... is has color defined by font-lock-keyword-face
> and a value has color defined by default face
>
> The mechanism of the hang is still unclear, but I found the cause of
> the font-lock malfunction: when using `up-list' to find the
> corresponding closing brace for an opening brace in an f-string, if
> the format specifier contains "#", the rest of the string is
> considered a comment and the search fails.  Therefore, it can be
> worked around by temporarily binding `parse-sexp-ignore-comments' to
> nil, as in the attached patch.
>
> Hangs on gef.py can also be avoided with this patch, but it assumes
> that the braces are properly closed.  If you remove the closing braces
> of expressions containing "#", it will eventually hang.
>

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