A GPL app can absolutely link to proprietary software and still be covered under the GPL.
From the GPLv3 itself.
> The “System Libraries” of an executable work include anything, other than the work as a whole, that (a) is included in the normal form of packaging a Major Component, but which is not part of that Major Component, and (b) serves only to enable use of the work with that Major Component, or to implement a Standard Interface for which an implementation is available to the public in source code form. A “Major Component”, in this context, means a major essential component (kernel, window system, and so on) of the specific operating system (if any) on which the executable work runs, or a compiler used to produce the work, or an object code interpreter used to run it.
Now you can't just go and include random proprietary jars in your app for whatever reason but but linking to the jar for the purposes of using the system notifications and background services seems to me like it would definitely count.
I personally would consider notifications and the ability to run in the background to be essential but there's a better test which is the reason that this exception exists in the first place.
From copyleft.org:
> The system library exception is designed to allow copylefted software to link with these libraries when prohibition of that linking would hurt software freedom more than it would hurt proprietary software.
This is really the core of it -- who is hurt more by disallowing this linking: Google or FOSS apps?
As a daily reminder, this piece of junk will be countermanded by Samsung, Lenovo and Huawei and whoever deploys AOSP as they use their own push platforms.
Note the GPLv2 doesn't allow the exception to apply if the library is distributed with the app. GPLv3 doesn't draw a distinction between distributing with the app or linking to something already on the system. But IANAL.
From the GPLv3 itself.
> The “System Libraries” of an executable work include anything, other than the work as a whole, that (a) is included in the normal form of packaging a Major Component, but which is not part of that Major Component, and (b) serves only to enable use of the work with that Major Component, or to implement a Standard Interface for which an implementation is available to the public in source code form. A “Major Component”, in this context, means a major essential component (kernel, window system, and so on) of the specific operating system (if any) on which the executable work runs, or a compiler used to produce the work, or an object code interpreter used to run it.
Now you can't just go and include random proprietary jars in your app for whatever reason but but linking to the jar for the purposes of using the system notifications and background services seems to me like it would definitely count.