TL;DR: It appears that Xcode now auto-updates overnight if your Mac is connected to power. I did a manual install, but the (stalled) auto-update still tries overnight. How do I kill this zombie? (Yes, I can turn off auto-update in App Store, but I don't want to. And anyway, the problem would persist when/if I turned it back on.)
Longer: The following steps happened
- Yesterday morning my Mac had the error dialog (paraphrasing here) "Could not update, you must quit Xcode"
- I quit Xcode
- Clicked "Update" in App Store app
- Update stalled at 90%, App Store said "Pending"
- (Simulator was still running; could have been the problem)
This stalling is a common problem, dealt with in many posts here, notably
Xcode update stuck after updating macOS
Xcode update stuck on "update"
- I went to https://developer.apple.com/download/more/ and got and installed the update by hand
- That wasn't the end of my problems; see Broken xib with xcode 10.3
- This morning, I was welcomed with the same "Could not update, you must quit Xcode" error dialog.
The App Store app still says "Pending" for this update. Apparently you used to be able to press the Option or Control-Option keys to reveal a "Cancel" button, but no longer.
Q: How do I cancel this pending update, short of de-installing current Xcode and re-starting the App Store process? (See How to Completely Uninstall Xcode and Clear All Settings)
Note: FWIW the file
~/Library/Application Support/App Store/updatejournal.plist seems to say my latest version is 9.2.
Note: another suggestion at https://apple.stackexchange.com/questions/345910/how-to-delete-partially-downloaded-updates-in-high-sierra is to delete all contents of $TMPDIR../C/com.apple.appstore/ but that seems drastic.
Note: In Launchpad, the Xcode icon has a blue dot next to it. Could my solution really be as simple as deleting the Xcode icon? Plenty of similar suggestions all over the web...
