How to use a local version of a package in spacemacs?

Question

This is similar to this question but the answer there seems to be deprecated.

Let's say I'm using a layer and want hack the code of a particular package that layer is using. How do I go about it?

---

To better illustrate what I want to accomplish in general, I present a specific example.

I try to get the spotify layer to work, but the current master branch in the helm-spotify package uses a deprecated web API. There is a pull request to fix this and I want to try it and maybe contribute something. My problem is, that I can not get the local copy of helm-spotify to load.

What I tried was to switch to the develop branch of spacemacs:

git branch --track develop origin/develop
git checkout develop

In ~/.emacs.d/layers/spotify/packages.el

I changed from

(setq spotify-packages '(spotify helm-spotify))

To

(setq spotify-packages
          '(    
                spotify
                (helm-spotify :location local)
           ))

And pulled the helm-spotify repository to ~/.emacs.d/layers/spotify/local/helm-spotify

When I restart spacemacs I get

File error: Cannot open load file, no such file or directory, multi

In when I look into helm-spotify.el there is:

(require 'multi)

So my guess is, that when installing helm-spotify from melpa the dependency on multi gets resolved prior to loading helm-spotify but of course not anymore when I use a local copy of helm-spotify.

So my questions are:

• How do resolve dependencies when using a local package?
• Or should I do this completely differently from what I described?

---

I also tried, without success, to add multi to dotspacemacs-additional-packages and to spotify-packages:

(setq spotify-packages '(
                         multi ;; I added this
                         spotify
                         (helm-spotify :location local) ;; I modified here
                         ))

;; I added this
(defun spotify/init-multi ()
  (use-package multi))

;; the rest is as it was

(defun spotify/init-spotify ()
  (use-package spotify
    :config (spacemacs/set-leader-keys
              "amsp" 'spotify-playpause
              "amsn" 'spotify-next
              "amsN" 'spotify-previous
              "amsQ" 'spotify-quit)))

(when (configuration-layer/layer-usedp 'spacemacs-helm)
  (defun spotify/init-helm-spotify ()
    (use-package helm-spotify
      :config (spacemacs/set-leader-keys
                "amsg" 'helm-spotify))))

in packages.el. Also tried without adding multi to dotspacemacs-additional-packages.

Answer 1

First, you should never modify the code in master branch, Spacemacs is designed to be hackable while keeping the master branch read-only, also not that force pushes to master branch may happen!. If you really want to modify the code you should use the develop branch and keep it up to date manually. Develop branch is never forced push.

EDIT: actually you were using the develop branch, my apologies, I let the paragraph for reference.

Now the answer :-) The correct way to do what you want is to overwrite the location in dotspacemacs-additional-packages. I just tried it by forking helm-spotify in my namespace and then added:

   dotspacemacs-additional-packages
     '((helm-spotify :location (recipe :fetcher github :repo "syl20bnr/helm-spotify")))

Then upon restart Spacemacs fetched the package from my fork correctly instead of reaching MELPA. Spacemacs uses quelpa to fetch repositories from GitHub based on MELPA recipes, package.el is used to install the packages so dependencies are correctly resolved.

Note that:

• you may have to manually delete the helm-spotify folder in ˜/.emacs.d/elpa directory and restart Emacs.
• You still have to add the spotify layer to your dotspacemacs-configuration-layers variable.