bug#34343: [PATCH] Make project--find-regexp-in-files work with remote files

[Dmitry Gutov <dgutov@yandex.ru>]

On 27.12.2019 10:24, Michael Albinus wrote:

> The patch looks reasonable to me. Since I don't use project-files, I
> can't say whether this works correctly.

Unless it's a religious position, you can test it with:

   M-x project-find-regexp

or

   M-x dired-do-find-regexp (also bound to 'A' in Dired)

(the latter since one of my yesterday's commits).

For now, I've done some testing myself. It prepended 'remote-id' twice, 
now fixed.

And some benchmarking.

While project-find-file (the command actually using project-files) 
completed fairly quickly with my remote connection (1 to 3 seconds), the 
regexp search took a while (like 50 seconds) when there are a lot of 
matches (~500).

Things I've noticed:

- (mapcar #'file-local-name files) takes like ~2 seconds when FILES only 
has ~3000 elements. The same code completes instantly on a local 
machine. Shouldn't it be the same?

- Most of the time is spent in 'find-buffer-visiting'. I wonder if that 
function's performance can be improved. For now I've decided to avoid 
calling it unless really necessary (so, no free syntax highlighting for 
Tramp users, even when the file is already visited).

Anyway, I also wanted to compare this to what we had before 
(dired-do-search), and that one doesn't work at all on remote 
directories. So it must be an improvement either way.

> Your use of remote-id reminds me of comint-file-name-prefix, which
> serves a similar purpose. Maybe you can check it in comint.el and the
> other packages where it is used, and steal some ideas from there :-)

Good suggestion, it could be a buffer-local var, or a field in 
xref-file-location. Or we could just avoid printing it in the group names.

The simplest fix is below, but it kind of requires file-local-name to be 
fast:

diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index bbd3940be4..5c38ae910c 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -142,7 +142,7 @@ xref-location-marker

  (cl-defmethod xref-location-group ((l xref-file-location))
    (cl-ecase xref-file-name-display
-    (abs (oref l file))
+    (abs (file-local-name (oref l file)))
      (nondirectory (file-name-nondirectory (oref l file)))))

  (defclass xref-buffer-location (xref-location)