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

   1 use crate::coherence::CoherenceError;
   2 use crate::ext::GoalExt;
   3 use crate::solve::Solver;
   4 use crate::RustIrDatabase;
   5 use chalk_ir::cast::*;
   6 use chalk_ir::interner::Interner;
   7 use chalk_ir::*;
   8 use tracing::{debug, instrument};
   9
  10 // Test if a local impl violates the orphan rules.
  11 //
  12 // For `impl<T> Trait for MyType<T>` we generate:
  13 //
  14 //     forall<T> { LocalImplAllowed(MyType<T>: Trait) }
  15 //
  16 // This must be provable in order to pass the orphan check.
  17 #[instrument(level = "debug", skip(db, solver))]
  18 pub fn perform_orphan_check<I: Interner>(
  19     db: &dyn RustIrDatabase<I>,
  20     solver: &mut dyn Solver<I>,
  21     impl_id: ImplId<I>,
  22 ) -> Result<(), CoherenceError<I>> {
  23     let impl_datum = db.impl_datum(impl_id);
  24     debug!(?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.solve(db, canonical_goal).is_some();
  36     debug!("overlaps = {:?}", is_allowed);
  37
  38     if !is_allowed {
  39         let trait_id = impl_datum.trait_id();
  40         return Err(CoherenceError::FailedOrphanCheck(trait_id));
  41     }
  42
  43     Ok(())
  44 }