allowing dead code should be transitive

[metajack]

Currently if you have some dead_code and you want to preserve it, you have to annotate every function you want to preserve and all the dead code that function calls.

I think we should consider annotated code to be alive, and then all the code that touches to be alive as well.

[alexcrichton]

cc @ktt3ja, sounds like a cool idea to me.

[ktt3ja]

By "annotate", do you mean putting an #[allow(dead_code)] attribute above the function you want to preserve?

[metajack]

@ktt3ja yes.