Type checker incorrectly allows passing of non-pointer values to pointers

[yorickpeterse]

Please describe the bug

When passing non-pointer values, such as a Foo or ref Foo, the type checker allows such values to be passed when a Pointer[T] is expected:

class Thing {}

fn example[T](value: Pointer[T]) -> Pointer[T] {
  value
}

class async Main {
  fn async main {
    example(Thing())
  }
}

This should produce a compile-time error, but it doesn't.

We should disallow passing anything to a Pointer unless the value itself is already a pointer.

Operating system

Fedora

Inko version

main