Tsconfig of a dependent lib not considered when building an app

[devdamiano]

It seems to me that the libraries' tsconfig.json files are not considered when building/serving an application that's dependent on them.

How do I make the lib's tsconfig file to be considered during app build/serve?
I see that you can make the lib buildable. It's considered then.
What are the other options? Because I also see that when you generate a lib, then you don't need to make it buildable and it still generates the tsconfigs... So there must be other options.