Tags: patch

0. cd "$(mktemp -d)"
1. touch .dir-locals.el
2. HOME="${PWD}" XDG_CONFIG_HOME="${PWD}/.config" emacs-28.2
3. M-x toggle-debug-on-error RET
4. M-: (setq project-vc-extra-root-markers (list dir-locals-file)) RET
5. M-x package-install RET eglot RET
6. C-x p g Package-Requires RET

Debugger entered--Lisp error: (void-function xref-show-xrefs)
  xref-show-xrefs(#f(compiled-function (&rest args2) #<bytecode -0xac14b28472c08a0>) nil)
  project-find-regexp("Package-Requires")
  funcall-interactively(project-find-regexp "Package-Requires")
  call-interactively(project-find-regexp nil nil)
  command-execute(project-find-regexp)

Emacs 28 ships with Xref 1.3.0, and without Eglot.  Eglot depends on
Project 0.9.3 directly and on Xref 1.4.0 transitively.  Yet package.el
for some reason deems that the built-in Xref 1.3.0 satisfies this
requirement, and does not pull a more recent version from GNU ELPA.

[ BTW, there is nothing special about steps 1, 4, 6 in the recipe above:
  they just demonstrate that the expected version of Xref is missing. ]

At first glance this sounds like a package.el bug, but since there won't
be an Emacs 28.3, and until someone checks whether it's present in Emacs
29+, perhaps something like the following is needed as a workaround?