When should type markers be attached?

[JustusAdam]

In #119 we decided to restore the old behavior on when markers are attached to types. This means a value only gets marked with it's type if it the return value of an external or marked function or if it is input to a controller.

Update: The old policy was unsound. Marker semantics have been made consistent and simplified. This is made possible by improved field sensitivity. Markers are now attached to every node of the marked type as well as

• nodes which are children (e.g. fields) of a marked type
• nodes which are parents of the marked type if it the children of this node are not separately tracked (overapproximation)

There are some residual questions as to how references are handled. For instance in the following case, should c be considered marked?

#[paralegal::marker(dangerous)]
struct Parent<'a> {
    child: &'a mut Child,
}

struct Child {
    field: usize,
}

#[paralegal::marker(sink, arguments = [0])]
fn sink<T>(_: T) {}

#[paralegal::analyze]
fn main() {
    let mut c = Child { field: 0 };
    let p = Parent { child: &mut c };
    sink(c);
}