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bug#23223: 25.0.92; Can xref-find-references be sped up?

From: Dmitry Gutov
Subject: bug#23223: 25.0.92; Can xref-find-references be sped up?
Date: Thu, 7 Apr 2016 03:11:25 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0

On 04/06/2016 08:12 PM, Eli Zaretskii wrote:

But using plain Grep has the same problem: Grep reports the hits, and
we then go ahead and visit each hit, right?

Using Grep has the slowness problem, but it doesn't have this opportunity for optimization, since Grep definitely doesn't know what characters constitute a symbol in different languages. But your proposal may speed up Grep searches too, so that's a plus.

How do I find the appropriate 'buffer' match in this line?

You already have the code that looks for the match in each line.  What
I had in mind is looking in the output of Grep or lid, instead of
visiting the file and looking in that file's buffer.  Does this make

Yes, but the search for \_<eval-when\_> needs a properly set syntax table, syntax-propertize-function, and possibly other variables that the latter might depend on. Basically, it needs a buffer in the right major mode. And switching major modes is actually not cheap:

(benchmark 230 '(with-temp-buffer (c-mode)))

=> 1.20s

in my working Emacs instance (much faster in a pristine one, admittedly). But I'll have a try at doing this while reusing the temporary buffer.

Some major modes could also trip over incomplete source code, but we'll get to that when we see that. Syntax highlighting seems out of the question, though, with high likelihood of getting it wrong.

We also have the possibility of syntax-propertize-function not applying the correct syntax classes to the code fragment because it doesn't see the whole file, but I guess it's a small-ish price to pay for the performance improvement, and could be fixed on a case-by-case basis.

Or can we ask 'lid' (and, ideally, Grep too) to include the column of a
match in the output?

No, I don't think such an option exists.  It could be a great
enhancement request, though ;-)

I was hoping you could serve as a liaison in that, being the sole user of id-utils that I know of, so far.

But anyway, if there is no such feature now, we have to choose another solution in Emacs 25.1. Even if id-utils were to add this today, it would take time to trickle to the majority of our users.

The bar is actually higher: to make use of the enhancement, we'd need Global and CScope to support it, too, or at least to be able to detect the feature at runtime.

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