Thanks for your question Jay and thanks your answer Ali Afshar!
Unfortunately I do not understand how Google believes the following scenario should work without the email address of the users:
In Documents List API v3 you could copy a file A to file B, retrieve the ACL-information of file A (including the users email adresses) and simply add them as ACL to file B.
With Drive API you can retrieve almost the same Permission information, but without the user email address, which is still required to re-share file B to the same users.
As a sidenote: If you use GAS DefaultService DocsList, you can still receive the editor/viewers with getEditors() or getViewers(). If you manually share a file you can see all email addresses as well.
So if you ask me, the privacy issue is a valuable argument, but it does simply not apply here.
Jan
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