bug#53758: 28.0.91; Recursive edit during dired-do-find-regexp-and-replace breaks isearch

[Juri Linkov <juri@linkov.net>]

> isearch-forward (C-s) while in a recursive edit (C-r) triggered from
> dired-do-find-regexp-and-replace (Q in a dired buffer) always fails to
> find any matches for any string, even if there are matches in the
> buffer.
>
> Steps to reproduce:
> 1. Open a dired buffer in a directory containing at least one file which
> contains some text (e.g. "Hello world")
> 2. Run dired-do-find-regexp-and-replace to replace "Hello" with
> "Goodbye" ("Q Hello RET Goodbye RET"); this will switch buffers
> to the first matching file.
> 3. Type C-r to enter a recursive edit (I'm guessing this runs
> (recursive-edit)?)
> 4. At the start of the buffer, run isearch-forward searching for "world"
> ("C-s world RET")
> 5. Note that the isearch fails despite "world" being in the buffer.
>
> For what it's worth, this interestingly doesn't happen with
> project-query-regexp-replace (which also does multi-file query-replace).

This is because of these lines in xref--query-replace-1:

         ;; Counteract the "do the next match now" hack in
         ;; `perform-replace'.  And still, it'll report that those
         ;; matches were "filtered out" at the end.
         (isearch-filter-predicate
          (lambda (beg end)
            (and current-beg
                 (>= beg current-beg)
                 (<= end current-end))))

Dmitry, could you please explain the comment above.
What I don't understand is where this
"the next match now" hack is in `perform-replace'?