bug#49208: 28.0.50; project-find-regexp's xref-mode result buffer is not editable

[Christian Tietze]

TL;DR: The `xref-mode' results of `project-find-regexp' are not editable. 
Something like `occur-edit-mode' is missing. 

1) Open a project via C-x p p
2) Select 'g' to find in project (project-find-regexp)
3) Search for a phrase that produces results
4) In the resulting Xref buffer, try to edit the results

Invoking `occur-edit-mode' manually doesn't do the trick. There appears to
be no way to use this Xref facility to edit around search results in-place.

Other packages like `wgrep' or `ag' support this. The fantastic-looking Xref
results of `project-find-regexp' don't. Would be great if that was added.

Cheers,
Christian

----

In GNU Emacs 28.0.50 (build 2, x86_64-apple-darwin19.6.0, NS appkit-1894.60 
Version 10.15.7 (Build 19H524))
 of 2021-03-15 built on mbp20.local
Repository revision: f2b0cfff93afeeb1b6d84bfce4bde83dbe4862cb
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2022
System Description:  macOS 11.4

Configured using:
 'configure --enable-locallisppath=/usr/local/share/emacs/site-lisp
 --infodir=/usr/local/Cellar/emacs-head@28/28.0.50_1/share/info/emacs
 --prefix=/usr/local/Cellar/emacs-head@28/28.0.50_1 --without-x
 --with-dbus --with-imagemagick --with-modules --without-pop
 --with-gnutls --with-rsvg --with-xml2 --with-xwidgets --with-ns
 --disable-ns-self-contained'

Configured features:
ACL DBUS GIF GLIB GMP GNUTLS IMAGEMAGICK JPEG JSON LCMS2 LIBXML2 MODULES
NOTIFY KQUEUE NS PDUMPER PNG RSVG THREADS TIFF TOOLKIT_SCROLL_BARS
XWIDGETS ZLIB

Important settings:
  value of $LANG: en_DE.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Occur

Minor modes in effect:
  TeX-PDF-mode: t
  treemacs-filewatch-mode: t
  treemacs-git-mode: deferred
  treemacs-fringe-indicator-mode: t
  global-git-commit-mode: t
  magit-auto-revert-mode: t
  show-paren-mode: t
  marginalia-mode: t
  global-edit-server-edit-mode: t
  xah-fly-keys: t
  delete-selection-mode: t
  which-key-mode: t
  selectrum-prescient-mode: t
  real-auto-save-mode: t
  global-real-auto-save-mode: t
  popup-buffers-mode: t
  all-the-icons-ibuffer-mode: t
  doom-modeline-mode: t
  override-global-mode: t
  shell-dirtrack-mode: t
  projectile-mode: t
  global-emojify-mode: t
  emojify-mode: t
  auto-dim-other-buffers-mode: t
  selectrum-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  global-visual-line-mode: t
  visual-line-mode: t
  transient-mark-mode: t

Load-path shadows:
(here was a list of 'hides' about org-mode checked out from git)

Features:
(shadow emacsbug calc-map calc-stat calc-vec calc-ext calc-menu
calc-aent calc calc-loaddefs calc-macs consult-imenu repeat tramp-cmds
tramp-cache highlight-indent-guides timezone texinfo toolbar-x reporter
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which-func magit-diff smerge-mode diff git-commit log-edit pcvs-util
add-log magit-core magit-autorevert magit-margin magit-transient
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coolj notmuch-query goto-addr icalendar notmuch-tag notmuch-lib
notmuch-compat epa-file edit-server php-mode mode-local imenu
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the-org-mode-expansions python-el-fgallina-expansions
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speedbar ezimage dframe gnus-art mm-uu mml2015 mm-view mml-smime smime
dig gnus-sum shr kinsoku svg dom gnus-group gnus-undo gnus-start
gnus-dbus dbus xml gnus-cloud nnimap nnmail mail-source utf7 netrc nnoo
gnus-spec gnus-int gnus-range message rmc puny rfc822 mml mml-sec epa
derived epg epg-config mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader gnus-win gnus nnheader gnus-util rmail
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data-fileicons data-faicons data-alltheicons hl-line modus-themes
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cl-extra help-mode use-package-ensure use-package-core projectile grep
compile text-property-search comint ansi-color ring ibuf-ext ibuffer
ibuffer-loaddefs thingatpt emojify advice apropos tar-mode arc-mode
archive-mode pcase ht dash auto-dim-other-buffers face-remap cus-start
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Memory information:
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 (symbols 48 107327 9)
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 (string-bytes 1 18012918)
 (vectors 16 239340)
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