Bootloop update from CM12 to CM13 without GApps

After upgrading from CM12.1 to CM13 on my OnePlus One (bacon), my phone got in a bootloop. It would start optimizing apps, and reboot, over and over again.

I realized that this was because I forgot to also flash the latest GApps (I used the built-in CM updater):

If you are on a 12.1 nightly, you can ‘dirty flash’ CM13 (read update like any sane person) as long as you also update your third party addons in the same pass. This means, if you use Xposed, OpenGapps, etc. flash a Marshmallow compatible version of them immediately after your CM13 flash. Source: A Marshmallowy CM.

However, simply flashing them after it didn’t help. The most important thing for me was that I could use the phone again.

After trying many things, I found a solution. I downgraded back to CM12.1, but at least the phone is booting again.

Note: I don’t know if this may result in some data loss. Please create a full backup just in case.

1. Get the latest CM 12.1 nightly from CyanogenMod Downloads
2. Start your device in recovery (volume down + power)
3. Connect your device to your PC
4. Transfer the CyanogenMod ZIP to your phone
5. Use adb to delete all GApps:

   adb shell
   rm -rf /data/app/com.google*
   rm -r /data/media/0/Android/data/com.google.*
   

6. Install the CyanogenMod ZIP
7. Reboot

Now your device should boot successfully. After this I could also flash the GApps for CM12.1 again, and it would still boot.