How do I use xref-find-definitions with multiple source directories?

Question

I'm attempting to make changes to an Emacs package. I currently have the version in use installed in ~/.emacs.d/elpa/<package> and the source checked out from git in /src/<package>.

When I navigate to, for example, fileA.el in /src/<package> and press M-. (xref-find-definitions) on an identifier in fileB.el, Emacs will jump into ~/.emacs.d/elpa/<package>/fileB.el. I would prefer if it instead jumped to /src/<package>/fileB.el.

Now, I've created a TAGS file, and that seems to work correctly if I call M-x xref-etags-mode prior to using M-.. However, I don't want to remember to do that for every buffer that I open. Is there an easier solution?

For clarity, /src/<package> is /not/ on my load-path (and I would like to keep it that way).

Answer 1

While working on its code, you can open /src/<packages>/fileA.el and call M-x eval-buffer. Do the same for the rest of the files in the said package that you might want to navigate to. That will make Emacs remember the new locations of the functions in this package.

This is a solution for the built-in elisp xref backend. Not need for xref-etags-mode for that.

Answer 2

Evaluating buffers proposed by Dmitry is what doesn't require any configuration.
But it may create additional mental load to remember eval-buffers.
Also it makes pristine installed package's functions inaccessible(without another eval-buffer).

A method with package system setup

Example with installed Helm package and a dev git repository. Code snippet in Emacs init.

(if (getenv "MYDEV")
    (progn
      ;; disable activation of some installed packages
      (setq package-load-list
            (append '((helm nil))
                    '((helm-core nil))
                    package-load-list))

      ;; add dev repository to `load-path'
      (add-to-list 'load-path "~/some_path_to_repo/helm")

      (package-initialize)

      ;; now load code from dev repository as its docs recommend
      (load "helm-config.el"))
  ;; else
  (package-initialize))

Then to launch in terminal an instance of Emacs that will use dev git repository:

[user@user-pc ~]$ MYDEV=on emacs

xref will jump to definitions of symbols in loaded files(git repo)