Incremental java compiler does not detect changes to classes used in type parameters in some cases

[big-guy]

Expected Behavior

Gradle build should fail when Java compilation should fail.

Current Behavior

Gradle build succeeds when Java compilation should fail.

Context

Given these classes:

interface Super <T> { 
	T getResult();
}

interface Sub extends Super<Deleted> { }

interface Deleted {}

If I delete Deleted, Sub should be recompiled (and fail compilation). I found this in the gradle/gradle codebase when deleting some classes.

The build fails if Sub has a reference to T or I disable incremental compilation.

A similar thing happens in a slightly simpler example:

interface Sub<T extends Deleted> { }

interface Deleted {}

It looks like we ignore the type parameters in some cases.

Steps to Reproduce

I reproduced the failure in a test:
#20479

Your Environment

This happens everywhere.

I tested 5.0, 6.0, 7.0 and 7.3/7.4/7.5. I think this has never worked.

[big-guy]

I poked around some more and there are more cases where this does the wrong thing:

interface Super<T extends Bar> { 
	T getResult();
}

interface Sub extends Super<Foo> { }

interface Bar {}
interface Foo extends Bar {}

If you change Foo so that it no longer extends Bar, Sub should be recompiled, but it isn't.