How to reproduce:
1. Open the attached project
2. Open AssetBundles -> OSX folder which is in the project
3. Delete created asset bundle and its manifests
4. In the editor build asset bundles Assets -> AssetBundles -> BuildAssetBundles
5. Notice a prompt "Moving file failed" (you will get it twice)
6. Click on cancel
7. Notice the errors "Building AssetBundle failed because hash collision was detected in the deterministic id generation."

This issue requires a refactor of a core system, which is currently in-progress. The development team expects this refactor to be complete in version 2018.1.0. At that time, this issue will be automatically re-opened and re-tested to verify the fix. In the interim, the Asset Bundle Browser (https://www.assetstore.unity3d.com/en/#!/content/93571) will detect and warn in most situations similar to this.

WON'T FIX: Contrary to our original plan, the new bundle build pipeline will not actually support variants at the low level. Variant support will be something dealt with at a higher level and will not actually utilize this same sort of file matching. As such we will not fix this exact case here, but the relevant use-case will be supported by the future high-level system.