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

[Dmitry Gutov <dgutov@yandex.ru>]

On 27.11.2020 22:14, Daniel Martín via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> 
> Scenario: A package customizes xref-show-refs-function to use a
> different UI to show xref results.  If that function does not return a
> valid xref buffer, then Dired's dired-do-find-regexp-and-replace (bound
> to Q by default) won't work anymore because it calls
> xref-query-replace-in-results on the buffer returned by
> xref--show-xrefs.

Oh, indeed. Thanks for the report.

> A workaround is that the package explicitly calls
> xref--show-xref-buffer, which is done for example at
> https://github.com/alexmurray/ivy-xref/commit/aa97103ea8ce6ab8891e34deff7d43aa83fe36dd,
> but it doesn't feel like an ideal solution because of the duplicated
> work.

It's too bad this wasn't reported a year ago.

> Is there a way dired-do-find-regexp-and-replace could not depend on an
> actual xref buffer to perform the replacement?

Well, there are options like:

  - Mandate that any xref-show-refs-function alternative has a 
corresponding feature that performs replacements in the matches.
  - Reimplement dired-do-find-regexp-and-replace entirely in terms of a 
different UI (e.g. create a faster dired-do-query-replace-regexp).

But in this particular scenario we can just override 
xref-show-xrefs-function to use the default behavior, see below.

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.

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)