JClass::from, JString::from, JThrowable::from, etc. safety

[uvlad7]

Shouldn't these be unsafe, as there are no is_instance_of/is_assignable_from checks inside?

[rib]

In general it's not expected to be a Rust/JNI safety issue to mix up object reference types (e.g. calling methods against the wrong class), since that usually leads to an exception which would be considered safe, even though it likely implies a bug.

Some specific JNI functions are more strict about the object types they are passed and jni-rs should (hopefully) already be using is_instance_of or similar for those cases.

[uvlad7]

I don't see any of these checks anywhere in the source code other than the tests.