From: Naofumi Yasufuku <naofumi@yasufuku.dev>
To: Alan Mackenzie <acm@muc.de>
Cc: 57318@debbugs.gnu.org
Subject: bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization
Date: Thu, 01 Sep 2022 01:01:56 +0900 [thread overview]
Message-ID: <m11qsw8kqz.fsf@yasufuku.dev> (raw)
In-Reply-To: <Yw5sQJcT9ypvMX14@ACM>
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Hello Alan,
Alan Mackenzie <acm@muc.de> writes:
> Hello, Naofumi.
>
> Thank you indeed for your bug report, and thanks even more for
> diagnosing the cause and writing a patch!
>
> I'm truly astounded that you managed to debug this problem, hidden as it
> was in the fontification parts of CC Mode, which are difficult to run
> with the debugger. Respect!
>
Thank you, I'm glad to hear that.
> Looking at your patch, I can see one or two problems with it. The main
> one is that after encountering a template opener "<", I'm a bit worried
> about the accuracy of checking for the matching ">".
>
> Looking further into the problem, it seems the misfontification bug was
> triggered by the commas in the template expressions. When there's a
> comma there, the (c-forward-<>-arglist ...) call (which "; Should always
> work") fails. This failure is caused by the dynamic binding of
> c-restricted-<>-arglists to t.
>
> When this dynamic binding is instead at nil (rather than t), the
> fontification works properly, with functions fontified as functions.
> The reason for this faulty binding was fixing a bug report where
> scrolling a buffer containing lots of templates was very slow. Binding
> c-restricted-<>-arglists to t "solved" that slowness.
>
Indeed. I confirmed that avoiding (c-restricted-<>-arglists t) binding
solves this misfontification problem at least, but it makes scrolling
terribly slow...
> That slowness had been caused by inefficient scanning of the template
> structures. I've now identified and implemented an alternative
> optimisation, which doesn't cause problems with commas in templates.
>
[..snip..]
> Can I ask you, please, to apply and test my proposed patch, which I
> enclose below. Would you please test it on your real C++ source code,
> and either confirm it really works, or say what's still faulty about it.
> If there are any problems with applying the patch, feel free to send me
> personal email.
>
I've applied your patch. It works well and solves misfontification
problem. At the same time, I've not seen any noticeable performance
degradation by this patch so far. Great.
attachment: fix_c-restricted--arglists_verification.png
I came across this problem when I tried to compare the current
tree-sitter's fontification quality and performance with familiar
cc-mode by using very-fast flat_hash_map code [1][2]. Now problematic
fontification has gone.
> So I must apologize that I won't be using your patch, but I thoroughly
> appreciate the time you must have spent debugging the problem.
>
That's just fine with me. I don't mind at all because I'm not an
expert. Fixing the root cause should be done.
Best regards,
Naofumi
[1] https://github.com/skarupke/flat_hash_map/blob/master/flat_hash_map.hpp
[2] https://probablydance.com/2017/02/26/i-wrote-the-fastest-hashtable/
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next prev parent reply other threads:[~2022-08-31 16:01 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-21 13:27 bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization Naofumi Yasufuku
2022-08-28 5:33 ` Naofumi Yasufuku
2022-08-30 20:00 ` Alan Mackenzie
2022-08-31 16:01 ` Naofumi Yasufuku [this message]
2022-08-31 19:26 ` Alan Mackenzie
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