config.vagrant.plugins source does not resolve correctly

[polarissunshine]

Vagrant version = Vagrant 2.4.1
Host Machine = Windows 10

I have a local .gem plugin for my project. The plugin works. I would like to add it as required plugin in the Vagrantfile. Due to the structure of the project I want the gem file in a directory up from the Vagrantfile, so other Vagrantfiles can also access the plugin gem. So I would like do:

config.vagrant.plugins = {"own-plugin" => {"version" => "0.1.0", "sources" => "../own-plugin-0.1.0.gem"}}

But I get this error

Install local plugins (Y/N) [N]: Y
Installing the 'own-plugin' plugin. This can take a few minutes...
Vagrant failed to initialize at a very early stage:

Vagrant failed to properly resolve required dependencies. These
errors can commonly be caused by misconfigured plugin installations
or transient network issues. The reported error is:

Unable to resolve dependency: user requested 'own-plugin (= 0.1.0)'

But all of this work.

config.vagrant.plugins = {"own-plugin" => {"version" => "0.1.0", "sources" => "own-plugin-0.1.0.gem"}}

vagrant plugin install ..\own-plugin-0.1.0.gem

vagrant plugin install ..\own-plugin-0.1.0.gem --local

I'm not sure why moving the gem file one directory up does not work with the config.vagrant.plugins.

I also tried to pass in the absolute path to the gem in the Vagrantfile, but that does not work either. Any workarounds or solution?