Was https://lists.gnu.org/archive/html/emacs-devel/2021-08/msg00340.html

Some guys symlink their PATH emacs to src/emacs.

Other guys still prefer `make install`, and live in constant fear of
meta-dotting into a .gz file.  Well, live in fear no more.

emacs -Q --eval "(custom-set-variables '(xref-prefer-source-directory t))"