Extend clauses.rs to support impl/dyn Trait

Author: KiChjang

chalk-solve/src/clauses.rs

@@ -3,6 +3,7 @@ use self::program_clauses::ToProgramClauses;
 use crate::RustIrDatabase;
 use chalk_ir::cast::{Cast, Caster};
 use chalk_ir::could_match::CouldMatch;
+use chalk_ir::fold::Subst;
 use chalk_ir::*;
 use rustc_hash::FxHashSet;
 use std::sync::Arc;
@@ -167,6 +168,17 @@ fn program_clauses_that_could_match(
                 }
             }
 
+            // Check for impl and dyn Traits so that we generate
+            // `Implemented(impl Foo + Bar) :- Implemented(Foo), Implemented(Bar)`
+            match trait_ref.self_type_parameter() {
+                Some(Ty::Opaque(qwc)) | Some(Ty::Dyn(qwc)) => {
+                    let self_ty = trait_ref.self_type_parameter().unwrap(); // This cannot be None
+                    let wc = Subst::apply(&[self_ty.cast()], &qwc.value);
+                    clauses.extend(wc.into_iter().casted());
+                }
+                _ => {}
+            }
+
             // TODO sized, unsize_trait, builtin impls?
         }
         DomainGoal::Holds(WhereClause::ProjectionEq(projection_predicate)) => {