How do you build one piece of the Android platform?

Question

I want to enhance Android app and I've cloned its source from android.git.kernel.org. During compile I find dependencies on platform components external to the tree, for example

com.google.android.collect.*

It turns out that most of these are resolved in platform/frameworks/base.git.

Which raises several questions:

• is grabbing a piece of the tree just asking for trouble, generally?
• can this be fixed with a .jar?
• how would one know which .jar and where to get it?
• is there a place that cross-references packages to .git trees?
• how do you detect? [and follow? [and resolve?]] dependencies?

Answer 1

is grabbing a piece of the tree just asking for trouble, generally?

If the "piece" is an app, and you are trying to build it as an app (and not as part of the overall firmware), I'd say "yes".

can this be fixed with a .jar?

Not that I am aware of. The firmware is not designed to be built piecemeal.