bug#44905: 27.1; Packages that customize xref-show-xrefs-function can break Dired's dired-do-find-regexp-and-replace

[Dmitry Gutov]

On 29.11.2020 14:57, Daniel Martín via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> Dmitry Gutov <dgutov@yandex.ru> writes:
> > While this change in the Right Thing(tm), I have to question the
> > wisdom of setting xref-show-xrefs-function to an Ivy or Helm-based
> > function, though. Those UIs serve to help you choose one item, whereas
> > commands like dired-do-find-regexp and project-find-regexp show the
> > user a list of matches, to interact with (usually) several of them.
>
> I agree with you, Ivy/Helm may not be the best UX for Xref, but this
> particular problem can still happen even if the user returns a buffer
> that represents the Xref data in a different way.  I think that
> xref-query-replace-in-results assumes certain invariants from the
> original *xref* buffer that are not documented.

True.

> > diff --git a/lisp/dired-aux.el b/lisp/dired-aux.el
> > index 94a2bbf1f3..4caafc8df6 100644
> > --- a/lisp/dired-aux.el
> > +++ b/lisp/dired-aux.el
> > @@ -3140,7 +3140,10 @@ dired-do-find-regexp-and-replace
> >             (query-replace-read-args
> >              "Query replace regexp in marked files" t t)))
> >        (list (nth 0 common) (nth 1 common))))
> > -  (with-current-buffer (dired-do-find-regexp from)
> > +  (defvar xref-show-xrefs-function)
> > +  (with-current-buffer
> > +      (let ((xref-show-xrefs-function 'xref--show-xref-buffer))
> > +        (dired-do-find-regexp from))
> >       (xref-query-replace-in-results from to)))
> >
> >   (defun dired-nondirectory-p (file)
>
> LGTM, thanks.

Eli, is this OK for Emacs 27.2?

Here's also a slightly more future-proofed version that avoids 
referencing the function we might want to rename/change later:

diff --git a/lisp/dired-aux.el b/lisp/dired-aux.el
index 94a2bbf1f3..26155190d4 100644
--- a/lisp/dired-aux.el
+++ b/lisp/dired-aux.el
@@ -3140,7 +3140,13 @@ dired-do-find-regexp-and-replace
           (query-replace-read-args
            "Query replace regexp in marked files" t t)))
      (list (nth 0 common) (nth 1 common))))
-  (with-current-buffer (dired-do-find-regexp from)
+  (require 'xref)
+  (defvar xref-show-xrefs-function)
+  (with-current-buffer
+      (let ((xref-show-xrefs-function
+             ;; Some future-proofing (bug#44905).
+             (eval (car (get 'xref-show-xrefs-function 'standard-value)))))
+        (dired-do-find-regexp from))
     (xref-query-replace-in-results from to)))

 (defun dired-nondirectory-p (file)