vendor/chalk-solve/src/coherence/orphan.rs

   1 use crate::coherence::CoherenceError;
   2 use crate::ext::GoalExt;
   3 use crate::solve::SolverChoice;
   4 use crate::RustIrDatabase;
   5 use chalk_ir::cast::*;
   6 use chalk_ir::interner::Interner;
   7 use chalk_ir::*;
   8
   9 // Test if a local impl violates the orphan rules.
  10 //
  11 // For `impl<T> Trait for MyType<T>` we generate:
  12 //
  13 //     forall<T> { LocalImplAllowed(MyType<T>: Trait) }
  14 //
  15 // This must be provable in order to pass the orphan check.
  16 pub fn perform_orphan_check<I: Interner>(
  17     db: &dyn RustIrDatabase<I>,
  18     solver_choice: SolverChoice,
  19     impl_id: ImplId<I>,
  20 ) -> Result<(), CoherenceError<I>> {
  21     debug_heading!("orphan_check(impl={:#?})", impl_id);
  22
  23     let impl_datum = db.impl_datum(impl_id);
  24     debug!("impl_datum={:#?}", impl_datum);
  25
  26     let impl_allowed: Goal<I> = impl_datum
  27         .binders
  28         .map_ref(|bound_impl| {
  29             // Ignoring the polarization of the impl's polarized trait ref
  30             DomainGoal::LocalImplAllowed(bound_impl.trait_ref.clone())
  31         })
  32         .cast(db.interner());
  33
  34     let canonical_goal = &impl_allowed.into_closed_goal(db.interner());
  35     let is_allowed = solver_choice
  36         .into_solver()
  37         .solve(db, canonical_goal)
  38         .is_some();
  39     debug!("overlaps = {:?}", is_allowed);
  40
  41     if !is_allowed {
  42         let trait_id = impl_datum.trait_id();
  43         Err(CoherenceError::FailedOrphanCheck(trait_id))?;
  44     }
  45
  46     Ok(())
  47 }