Xcode 6.2 fails to download docsets, complains they're “untrusted”

Question

The docsets I seek are Xcode 6.2 and iOS 8.2 . The machine is running an old macOS and can't be upgraded. Every time I click on offered items under "Preferences->Downloads->Documentation" I see the progress bar showing my request is acknowledged but then it halts halfway with the alert Could not download and install Xcode 6.2. The package “DevToolsDocset.pkg” is untrusted. I tried setting the date several years back but got another more verbose and less helpful alert message.

"Untrusted package" alert (imgur)

So, do there exist direct download links for Xcode 6.2 and iOS 8.2 docsets? What's a workaround to get them?

Answer 1

The solution came by itself quite unexpectedly so I'm sharing my trial and error experience:

1. Under Preferences->Downloads->Documentation click on any link to start the download.
2. Launch Disk Utility . When the alert pops up watch closely for a mounted disk image to appear at the left in the source list box. At this point you may quit Xcode.
3. While in Disk Utility : with the mounted disk image icon and its hierarchy expanded hover over the greyed out icon of the displayed media, highlight it and choose the "Mount" command from the "File" dropdown menu.
4. The Disk Image Mounter window opens: it will contain the docset's package. Click on it to install and either make the certificate trustable (under View certificate ) or hit Continue . The docset file will be installed to the root of your volume at /
5. You now may safely copy the docset from / to /Applications/Xcode.app/Contents/Developer/Documentation/DocSets by simply dragging over existing objects and replacing with the dragged docset upon the prompt.
6. Launch Xcode . The documentation will now be available. Repeat steps 1-5 for every docset you need.
7. Eject the docset's disk image in Disk Utility .