Share Chatter files across communities... or not

"One version of the truth" is the holy grail in content management. Chatter Files is salesforce.com's solution for allowing users to manage document revisions in Salesforce, while making sure that links to the file always give people the latest version. But with Communities, "one version of the truth" becomes more difficult to achieve.

Take the following scenario:

1. John Doe collaborates with internal users to create a pitch deck for a new product.
2. John uploads the file to the Competitive Advantage Chatter group in his org's internal community.
3. Several iterations later, the deck is ready to be shared in his company's partner community, called AllianceNet.
4. John uses the Global Header to switch from his org's internal community to the AllianceNet community.
5. John goes to the All AllianceNet group to share the file, already stored in Chatter, with the group, but... where's the file?

As it stands in Winter '15, files created or uploaded to one community, internal or external, can only be shared within that same community in Chatter. So, to share a file across communities, users effectively have to recreate a duplicate instance of the file by uploading it again as a new file to the new community.

The only way that files can be shared or seen across communities is to create a Salesforce CRM Content library that's shared with users who have access to multiple communities. But even then, users will not be able to attach the file to a Chatter post. They'll be able to find the file in Global Search, and share URL links to the file, but unfortunately "native" Chatter file attachments will not be possible.

If this limitation with file sharing across communities affects or bothers you, please promote the idea, "Sharing Files from Chatter to Communities".