Question about dired-do-find-regexp and xref-collect-matches

[Eric Abrahamsen]

A while ago I switched to the fish shell, which I generally like better
than bash.

A bit after that I noticed that marking files in Dired and using "A"
(dired-do-find-regexp) to search them was extraordinarily slow. Going up
a level to the parent directory and only marking the child directory,
the search was nearly instantaneous. But that meant I had to search all
the files in the child directory.

I suspected it was something to do with fish, and indeed setting
shell-file-name to "/usr/bin/bash" sped it up a little -- but that's a
bug report for another day.

While poking around I also noticed that dired-do-find-regexp calls
xref-collect-matches once per marked file. That means a full find+grep
call for each file, when a single find+grep call (or even just a single
grep call!) would do the trick.

The search hits are collected as:

(mapcan
 (lambda (file)
   (xref-collect-matches regexp "*" file
                         (and (file-directory-p file)
                              ignores)))
 files)

But the second argument to `xref-collect-matches' can be a
space-separated string of file names -- wouldn't it be easier just to
call `xref-collect-matches' once?

Eric