bug#62837: [PATCH] Add a semantic-symref backend which uses xref-matches-in-files

[Dmitry Gutov <dgutov@yandex.ru>]

On 16/04/2023 00:56, sbaugh@catern.com wrote:

>> Perhaps you could describe your case where you *did* see a significant
>> improvement from this patch, and we can discuss the best steps to
>> address that.
> 
> In short: I have a project.el backend for a large monorepo which has a
> project-files backend which returns only the subset of files which are
> relevant to work happening in a given clone.  (Generally a user will
> have many clones and be doing different work in each one.)  The
> relevant-files subset is determined by integration with the build
> system.
> 
> So running find returns a vast number of files and then searches over
> those, whereas running a search over project-files searches a much
> smaller number of files.

Neat.

> Regarding your medium-term plans to improve project-files performance -
> wildly guessing, but perhaps you have in mind a way to run a subprocess
> that outputs the project-files list?  Let's call it
> "project-files-process".  And then project-files-process could be piped
> to grep instead, for maximum efficiency?  If that was the idea, then my
> own backend could certainly have a project-files-process implementation
> too, for maximum efficiency.

That might be step number 3, although I'm not sure yet which kind of 
code will be required for the piping to be done efficiently enough.

The other two things I was looking at are:

- Use relative file names (less text to parse, memory to allocate, GC to 
thrash). The awkward part is how to merge that with the idea that 
project-files can include files from directories ("external roots"). 
Split those off into a different method? Treat them as separate projects 
to flat-map the lists of files at?

- Add arguments to allow filtering the files using the underlying tool. 
That can also result is much fewer files to parse in the output under 
suitable circumstances (e.g. we'd be able to pass a list of globs here).

There is one implementation of the second item in the branch 
scratch/etags-regen.

And both items need to be done carefully enough to maintain some 
backward compatibility.

So unless you're in a hurry, give me a few weeks to get around to this.

Further suggestions and patches are welcome, of course.