Add chalk rules related to associated type defs

* Rule ProjectionEq-Skolemize
* Rule WellFormed-AssocTy
* Rule Implied-Trait-From-AssocTy

Author: scalexm

src/librustc_traits/lowering.rs

@@ -362,7 +362,7 @@ fn program_clauses_for_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId
                 .map(|wc| tcx.mk_goal(GoalKind::from_poly_domain_goal(wc, tcx))),
         ),
     };
-    tcx.intern_clauses(&[Clause::ForAll(ty::Binder::dummy(clause))])
+    tcx.mk_clauses(iter::once(Clause::ForAll(ty::Binder::dummy(clause))))
 }
 
 pub fn program_clauses_for_type_def<'a, 'tcx>(
@@ -430,10 +430,86 @@ pub fn program_clauses_for_type_def<'a, 'tcx>(
 }
 
 pub fn program_clauses_for_associated_type_def<'a, 'tcx>(
-    _tcx: TyCtxt<'a, 'tcx, 'tcx>,
-    _item_id: DefId,
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    item_id: DefId,
 ) -> Clauses<'tcx> {
-    unimplemented!()
+    // Rule ProjectionEq-Skolemize
+    //
+    // ```
+    // trait Trait<P1..Pn> {
+    //     type AssocType<Pn+1..Pm>;
+    // }
+    // ```
+    //
+    // `ProjectionEq` can succeed by skolemizing, see "associated type"
+    // chapter for more:
+    // ```
+    // forall<Self, P1..Pn, Pn+1..Pm> {
+    //     ProjectionEq(
+    //         <Self as Trait<P1..Pn>>::AssocType<Pn+1..Pm> =
+    //         (Trait::AssocType)<Self, P1..Pn, Pn+1..Pm>
+    //     )
+    // }
+    // ```
+
+    let item = tcx.associated_item(item_id);
+    debug_assert_eq!(item.kind, ty::AssociatedKind::Type);
+    let trait_id = match item.container {
+        ty::AssociatedItemContainer::TraitContainer(trait_id) => trait_id,
+        _ => bug!("not an trait container"),
+    };
+    let trait_ref = ty::TraitRef::identity(tcx, trait_id);
+
+    let projection_ty = ty::ProjectionTy::from_ref_and_name(tcx, trait_ref, item.ident);
+    let placeholder_ty = tcx.mk_ty(ty::UnnormalizedProjection(projection_ty));
+    let projection_eq = WhereClause::ProjectionEq(ty::ProjectionPredicate {
+        projection_ty,
+        ty: placeholder_ty,
+    });
+
+    let projection_eq_clause = ProgramClause {
+        goal: DomainGoal::Holds(projection_eq),
+        hypotheses: &ty::List::empty(),
+    };
+
+    // Rule WellFormed-AssocTy
+    // ```
+    // forall<Self, P1..Pn, Pn+1..Pm> {
+    //     WellFormed((Trait::AssocType)<Self, P1..Pn, Pn+1..Pm>)
+    //         :- Implemented(Self: Trait<P1..Pn>)
+    // }
+    // ```
+
+    let trait_predicate = ty::TraitPredicate { trait_ref };
+    let hypothesis = tcx.mk_goal(
+        DomainGoal::Holds(WhereClause::Implemented(trait_predicate)).into_goal()
+    );
+    let wf_clause = ProgramClause {
+        goal: DomainGoal::WellFormed(WellFormed::Ty(placeholder_ty)),
+        hypotheses: tcx.mk_goals(iter::once(hypothesis)),
+    };
+
+    // Rule Implied-Trait-From-AssocTy
+    // ```
+    // forall<Self, P1..Pn, Pn+1..Pm> {
+    //     FromEnv(Self: Trait<P1..Pn>)
+    //         :- FromEnv((Trait::AssocType)<Self, P1..Pn, Pn+1..Pm>)
+    // }
+    // ```
+
+    let hypothesis = tcx.mk_goal(
+        DomainGoal::FromEnv(FromEnv::Ty(placeholder_ty)).into_goal()
+    );
+    let from_env_clause = ProgramClause {
+        goal: DomainGoal::FromEnv(FromEnv::Trait(trait_predicate)),
+        hypotheses: tcx.mk_goals(iter::once(hypothesis)),
+    };
+
+    let clauses = iter::once(projection_eq_clause)
+        .chain(iter::once(wf_clause))
+        .chain(iter::once(from_env_clause));
+    let clauses = clauses.map(|clause| Clause::ForAll(ty::Binder::dummy(clause)));
+    tcx.mk_clauses(clauses)
 }
 
 pub fn program_clauses_for_associated_type_value<'a, 'tcx>(
@@ -442,10 +518,11 @@ pub fn program_clauses_for_associated_type_value<'a, 'tcx>(
 ) -> Clauses<'tcx> {
     // Rule Normalize-From-Impl (see rustc guide)
     //
-    // ```impl<P0..Pn> Trait<A1..An> for A0
-    // {
+    // ```
+    // impl<P0..Pn> Trait<A1..An> for A0 {
     //     type AssocType<Pn+1..Pm> = T;
-    // }```
+    // }
+    // ```
     //
     // FIXME: For the moment, we don't account for where clauses written on the associated
     // ty definition (i.e. in the trait def, as in `type AssocType<T> where T: Sized`).
@@ -492,7 +569,7 @@ pub fn program_clauses_for_associated_type_value<'a, 'tcx>(
                 .map(|wc| tcx.mk_goal(GoalKind::from_poly_domain_goal(wc, tcx))),
         ),
     };
-    tcx.intern_clauses(&[Clause::ForAll(ty::Binder::dummy(clause))])
+    tcx.mk_clauses(iter::once(Clause::ForAll(ty::Binder::dummy(clause))))
 }
 
 pub fn dump_program_clauses<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {

src/test/ui/chalkify/lower_trait.rs

@@ -10,11 +10,12 @@
 
 #![feature(rustc_attrs)]
 
+trait Bar { }
+
 #[rustc_dump_program_clauses] //~ ERROR program clause dump
-trait Foo<S, T, U> {
-    fn s(_: S) -> S;
-    fn t(_: T) -> T;
-    fn u(_: U) -> U;
+trait Foo<S, T: ?Sized> {
+    #[rustc_dump_program_clauses] //~ ERROR program clause dump
+    type Assoc: Bar + ?Sized;
 }
 
 fn main() {

src/test/ui/chalkify/lower_trait.stderr

@@ -1,14 +1,23 @@
 error: program clause dump
-  --> $DIR/lower_trait.rs:13:1
+  --> $DIR/lower_trait.rs:15:1
    |
 LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: FromEnv(S: std::marker::Sized) :- FromEnv(Self: Foo<S, T, U>).
-   = note: FromEnv(T: std::marker::Sized) :- FromEnv(Self: Foo<S, T, U>).
-   = note: FromEnv(U: std::marker::Sized) :- FromEnv(Self: Foo<S, T, U>).
-   = note: Implemented(Self: Foo<S, T, U>) :- FromEnv(Self: Foo<S, T, U>).
-   = note: WellFormed(Self: Foo<S, T, U>) :- Implemented(Self: Foo<S, T, U>), WellFormed(S: std::marker::Sized), WellFormed(T: std::marker::Sized), WellFormed(U: std::marker::Sized).
+   = note: FromEnv(<Self as Foo<S, T>>::Assoc: Bar) :- FromEnv(Self: Foo<S, T>).
+   = note: FromEnv(S: std::marker::Sized) :- FromEnv(Self: Foo<S, T>).
+   = note: Implemented(Self: Foo<S, T>) :- FromEnv(Self: Foo<S, T>).
+   = note: WellFormed(Self: Foo<S, T>) :- Implemented(Self: Foo<S, T>), WellFormed(S: std::marker::Sized), WellFormed(<Self as Foo<S, T>>::Assoc: Bar).
 
-error: aborting due to previous error
+error: program clause dump
+  --> $DIR/lower_trait.rs:17:5
+   |
+LL |     #[rustc_dump_program_clauses] //~ ERROR program clause dump
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: FromEnv(Self: Foo<S, T>) :- FromEnv(Unnormalized(<Self as Foo<S, T>>::Assoc)).
+   = note: ProjectionEq(<Self as Foo<S, T>>::Assoc == Unnormalized(<Self as Foo<S, T>>::Assoc)).
+   = note: WellFormed(Unnormalized(<Self as Foo<S, T>>::Assoc)) :- Implemented(Self: Foo<S, T>).
+
+error: aborting due to 2 previous errors