Re: vc-git-grep vs project-find-regexp

[Dmitry Gutov]

Hi!

On 21/08/2023 18:29, Nicolás Ojeda Bär wrote:
> While it seems to work well, project-find-regexp seems much slower
> than vc-git-grep. After you execute the command, it pauses for what it
> feels a long time (~2s in a medium-size codebase) before showing the
> results. vc-git-grep on the other hand, starts displaying results
> immediately.

Have you tried measuring the time until Grep finishes too (not just 
until the output buffer is shown)? It's likely to be faster by that 
measure as well (for the moment), but that's not a certainty. Just 
curious how those compare as well.

> Is there a good reason for this difference? The only visible
> difference between both commands is that project-find-regexp's results
> are displayed in a XREF buffer while vc-git-grep uses Grep mode.

Xref uses a couple of abstractions to be able to show information from 
different sources. That has a cost, however. To be able to show the 
results buffer right away (while the search is in progress), requires 
more effort, including:

- Listing files in a project asynchronously (so that intermediate 
reporting is possible) with performance comparable to the synchronous 
approach, simply is order not to regress on that speed (there is some 
progress, I think, in the latest messages in bug#64735).

- To build on that, using some more advanced data structures than just 
lists for project files and search matches. Lazy sequences of futures, 
maybe.

The ability to abort a search in progress will require some thought too: 
currently it comes for free with 'C-g' in Xref; in Grep it's one 'C-c 
C-c' away because the reference to the process is available; but if we 
do an opaque data structure, it could need an "abort" primitive as well.