Custom plugins should now be placed in snap/plugins.

introduced in snapcraft 2.26

Originally snapcraft custom plugins were designed to be put in parts/plugins to avoid over-polluting the local directory with too many artifacts. A few problems manifested with this approach:

  1. Many just deleted the parts directory where the plugins lived in to start over and were confused when their plugins suddenly weren’t found.
  2. The need for new files in the layout.

As a result, a new schema was needed. The new design introduces the snap directory to hold all specific snapcraft assets,

with this in mind a new location was set for custom plugins, and that is snap/plugins/<plugin-name>.

To move to the new schema, for plugins all you need to do is:

mkdir snap
mv parts/plugins snap/

and apply those changes to your VCS if you are using one.