Function check_orphan_rules 

pub fn check_orphan_rules<'db>(db: &'db dyn HirDatabase, impl_: ImplId) -> bool

Checks whether the impl satisfies the orphan rules.

Given impl<P1..=Pn> Trait<T1..=Tn> for T0, an impl is valid only if at least one of the following is true:

• Trait is a local trait
• All of
  • At least one of the types T0..=Tn must be a local type. Let Ti be the first such type.
  • No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)