Support ANSIBLE_COLLECTIONS_PATH environment var

[nre-ableton]

This commit adds supports for reading ANSIBLE_COLLECTIONS_PATH from the environment, in a similar manner to how ANSIBLE_ROLES_PATH is handled.

—---

Fixes #3663

[zhan9san]

Hi @nre-ableton

Thanks for your work.

IMHO, even if you extend the collection paths, the molecule will also install dependencies into ~/.cache/ansible-compat/hash-vaule/, which is an isolated cache path defined in ansible-compat package.

You can find more details in ansible-compat package.

Are you sure the test result is correct?

[nre-ableton]

@zhan9san Yes, molecule behaves the same with roles. I wish that molecule had proper offline support, but that is a separate discussion (see ansible/galaxy#2030).

For this to work, prerun: false must also be set in the scenario's molecule.yml file. With that in place, molecule will install collections to ANSIBLE_COLLECTIONS_PATH.

[zhan9san]

I wonder if we can introduce an offline mode, no need to install dependencies when run molecule. But instead, we can install them in a cache path on CI server in advance, and let molecule respect this cache path.

---
dependency:
  name: galaxy
  offline: true
  role-file: requirements.yml
  requirements-file: collections.yml

Please allow me to explain it in detail.

Internet access

Currently, there are two kinds of dependencies need to be downloaded from internet when run molecule dependency.

1. role dependencies which are defined in [project-root-dir]/requirements.yml
2. dependencies for testing the role in different scenarios, which are defined in role-file: requirements.yml and requirements-file: collections.yml in [project-root-dir]/molecule/[scenario-name]/molecule.yml, referring to molecule.dependency.ansible_galaxy.AnsibleGalaxy

Installation location

Assume the my role name is my_role_2.

For the 1st, the dependencies will be installed by ansible-compat in /Users/jackzhang/.cache/ansible-compat/0afefd/roles and /Users/jackzhang/.cache/ansible-compat/0afefd/collections.

For the 2nd, the dependencies for scenario test will be installed by molecule in /Users/jackzhang/.cache/molecule/my_role_2/default/roles and /Users/jackzhang/.cache/molecule/my_role_2/default/collections

Then, the installed location would be as below.

1. /Users/jackzhang/.cache/ansible-compat/0afefd/roles
2. /Users/jackzhang/.cache/ansible-compat/0afefd/collections
3. /Users/jackzhang/.cache/molecule/my_role_2/default/roles
4. /Users/jackzhang/.cache/molecule/my_role_2/default/collections
5. /Users/jackzhang/.cache/molecule/my_role_2/scenario-2/roles
6. /Users/jackzhang/.cache/molecule/my_role_2/scenario-2/collections
7. /Users/jackzhang/.cache/molecule/my_role_2/scenario-3/roles
8. /Users/jackzhang/.cache/molecule/my_role_2/scenario-3/collections
9. other scenaios, etc.

Unified location

As we can see, there are many different locations. If we install them in one unified location, and ensure molecule respects it, this issue would be solved.

Let me know what you think.

[nre-ableton]

@zhan9san I think that this would be a great idea, and I wouldn't mind to implement something like this. Offline mode would be very useful for us. However, I also think that it is a bit beyond the scope of this PR. 😁 I'll go ahead and un-draft this PR, unless you have any strong objections.

[zhan9san]

LGTM.
Go ahead please

[nre-ableton]

@zhan9san Thanks for the merge!