Propagation From Type Parameters

[IGI-111]

CS-FSSA-013

Sway's type system ignores some hints about the type of variables. Let us consider the following
example:

trait Build {
 fn build() -> Self;
}
fn produce<T>() -> T
where
 T: Build,
{
 T::build()
}
impl Build for u32 {
 fn build() -> Self {
 31
 }
}
impl Build for u64 {
 fn build() -> Self {
 63
 }
}
fn consume(a: u32) {}
fn main() {
 let x = produce();
 consume(x);
}

Here we instantiate variable x with the result of produce(). Since produce() returns a generic type,
the concrete type of x cannot be determined just yet: it can either be u64 or u32. Since x is later passed
to consume(), which only accepts u32, type inference should assign this type to x. However, the
compiler fails to use this information and rejects the program, as it assumes x to be of type u64.