Ensure recovery supports installing Ubuntu Touch

[amartinz]

See: ubports/halium_bootable_recovery#22

[NeoTheThird]

recoveries are updated over systemimage, right? so we can assume it to be there after the next ota? we'll probably also have to update some configs (eg https://github.com/ubports/installer-configs/blob/master/v2/devices/FP2.yml#L48) to make sure we're downloading the right version.

[amartinz]

this depends on the device.

what do you think about adding a new method to call in the installer config to verify recovery?
devices with supported recovery could then opt-in to check recovery.

until most devices are updated and we can move the check to be opt-out.

[NeoTheThird]

Some prerequisites for this in ubports/promise-android-tools#61.

Making it opt-in during the rollout is a good idea. I can imagine two ways this could be done.

a) The systemimage:install step could be given an optional verify_recovery property, which could trigger a global handler

      - actions:
          - systemimage:install:
                verify_recovery: true

b) A special systemimage:assert_capable_recovery step or generic adb:assert_prop step

      - actions:
          - adb:assert_prop:
              property: "ro.ubuntu.recovery"
              value: "true"
          - systemimage:assert_capable_recovery:
        fallback:
          - <steps needed to install a capable recovery>

[amartinz]

i really like the potential scaling and possibilities of an assert_prop call.
something like this would be really useful, especially if extented a bit, like being able to check if:

• equal (every type, also allows for checking if empty)
• greater than (numeric)
• less than (numeric)
• starts with
• ends with
• contains

then it we can also reuse that to also implement a), which does the ro.ubuntu.recovery check under the hood.

[NeoTheThird]

i think we should be able to implement regex support there, that way all of those things could be done! Also, very good point, it doesn't have to be one or the other! the systemimage step is already implemented as a sort of meta-step that just "creates" steps to be executed by other plugins, so the actual logic does not need to be duplicated. kinda excited about the possibilities of this :]