`skip checkup` fails unless users manually install Android Studio

[dfabulich]

https://skiptools.slack.com/archives/C078X69G8F2/p1769285204483659

Two users report that skip checkup fails with this error in the logs:

SDK location not found. Define a valid SDK location with an ANDROID_HOME environment variable or by setting the sdk.dir path in your project's local properties file

One user reported that manually installing Android Studio fixes it

[dfabulich]

See also #605

[dfabulich]

https://github.com/orgs/skiptools/discussions/601#discussioncomment-15687677

I've done some testing now on a blank macOS install via UTM. It's not at all clear to me how any of this was supposed to work without Android Studio.

The 1.7.0 Skip Homebrew formula installs android-commandlinetools which is, itself, an Android SDK.

Default Android SDK root is $HOMEBREW_PREFIX/share/android-commandlinetools

That means that you could export ANDROID_HOME=/opt/homebrew/share/android-commandlinetools and it'll work. (You'd need to use the sdkmanager to accept licenses.)

But we never documented setting ANDROID_HOME to that, and no code in Skip is configured to automatically attempt to use that if $ANDROID_HOME isn't set. Instead, Skip is configured to automatically check ~/Library/Android/sdk (which is managed by Android Studio) and use that as an $ANDROID_HOME.

As far as I can tell, Skip is installing the android-commandlinetools but we're not actually using them for anything.

The only thing Skip is currently using is android-platform-tools, and for that, we're really just using adb. But if you try to actually use android-commandlinetools to build an Android app, it's going to install its own copy of adb in /opt/homebrew/share/android-commandlinetools/platform-tools/adb.

IMO, android-platform-tools kinda shouldn't exist. Anybody who wants them should use android-commandlinetools and then sdkmanager platform-tools to install the platform tools, including adb. I've filed two issues on this:

• Use adb from $ANDROID_HOME/platform-tools skipstone#178
• Stop installing android-platform-tools homebrew-skip#3

So, I can imagine a few different approaches here, listed here in order of my preference.

1. We could just tell users to install Android Studio. Skip "just works" like that today. That's what I've done in Add Android Studio requirement to getting started guide skip.dev#10 We could link to optional "non Android Studio" instructions to install android-commandlinetools and use sdkmanager, setting the ANDROID_HOME environment variable to its SDK root. If we fixed #178 then Skip would find adb in $ANDROID_HOME/platform-tools/adb. (I think, if we did it this way, we'd remove android-commandlinetools as well as android-platform-tools from the Skip Homebrew formula.)
2. We could make Skip try hard to use android-commandlinetools and avoid Android Studio. We'd tell users to (manually) set ANDROID_HOME to $HOMEBREW_PREFIX/share/android-commandlinetools, so gradle will work from the command line, but skip gradle would ignore the user's $ANDROID_HOME, and enforce the use of Homebrew's Android SDK. (The big drawback with this approach is that if users install Android Studio, they'll have a separate SDK folder, a separate collection of system images, etc. That can quickly add up to dozens of GB of wasted disk.)
3. We could check to see if ~/Library/Android/sdk exists and use it; if it doesn't, we could use $HOMEBREW_PREFIX/share/android-commandlinetools. But for anyone who does install Android Studio, that would still leave two SDKs on their machine, which is confusing.
4. We could check to see if ~/Library/Android/sdk exists and use it; if it doesn't, we could make a symlink from there to $HOMEBREW_PREFIX/share/android-commandlinetools, and then use that. (But if the user later installs Android Studio, I don't know what it's going to do. In the best-case scenario, Android Studio and Homebrew would share their Android SDK, but, in the worst case, they might conflict in weird ways.)