bug#23179: 25.0.92; Restore `M-,' to continue etags search

[Dmitry Gutov]

On 04/02/2016 09:58 AM, Eli Zaretskii wrote:

> But we could have a tags-only command that presented an xref UI, I
> think.  (Its name could be "tags-search" ;-)

Probably not tags-search; we're only deprecating some etags commands, 
but not removing them (yet?). And why is etags so special that it needs 
its own find-regexp command, but other backends don't?

Anyway, this should get you going:

(defun tags-find-regexp (regexp)
  (interactive "sTags search (regexp): ")
  (let* ((files
          (save-excursion
            (let ((enable-recursive-minibuffers t))
              (visit-tags-table-buffer))
            (mapcar #'expand-file-name (tags-table-files))))
         (xrefs (cl-mapcan
                 (lambda (file)
                   (xref-collect-matches regexp "*" file nil))
                 files)))
    (unless xrefs
      (user-error "No matches for: %s" regexp))
    (xref--show-xrefs xrefs nil t)))

(I don't know if calling 'find' once per file is an actual problem, but 
it's likely suboptimal; we'll fix that in a unified fashion later).