Features thus far seem to be used specifically in ndk-sys to prevent linking against additional libraries, for content that is provided outside of libandroid.so:

https://github.com/rust-windowing/android-ndk-rs/blob/d104d01f116b537babdc94d8c9889581f8d63a02/ndk-sys/src/lib.rs#L43-L53

However, hardware_buffer and trace have their content available directly in libandroid.so - making these features only guard Rust code, in my eyes unnecessarily. It seems much more clear to enable everything libandroid.so has to offer solely when a certain API level is turned on. After all, we don't replicate this feature guarding pattern for other "subsystems" of the Android API, only for tracing and hardware_buffer.

@JasperDeSutter What's your thought on this?