Auto merge of #49626 - fanzier:chalk-lowering, r=scalexm

Implement Chalk lowering rule Normalize-From-Impl

This extends the Chalk lowering pass with the "Normalize-From-Impl" rule for generating program clauses from a trait definition as part of #49177.

r? @nikomatsakis

Author: bors

Diff for: src/librustc/ich/impls_ty.rs

@@ -1373,6 +1373,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for traits::DomainGoal<'tcx>
             FromEnv(where_clause) => where_clause.hash_stable(hcx, hasher),
 
             WellFormedTy(ty) => ty.hash_stable(hcx, hasher),
+            Normalize(projection) => projection.hash_stable(hcx, hasher),
             FromEnvTy(ty) => ty.hash_stable(hcx, hasher),
             RegionOutlives(predicate) => predicate.hash_stable(hcx, hasher),
             TypeOutlives(predicate) => predicate.hash_stable(hcx, hasher),

Diff for: src/librustc/traits/mod.rs

@@ -267,6 +267,7 @@ pub enum DomainGoal<'tcx> {
     WellFormed(WhereClauseAtom<'tcx>),
     FromEnv(WhereClauseAtom<'tcx>),
     WellFormedTy(Ty<'tcx>),
+    Normalize(ty::ProjectionPredicate<'tcx>),
     FromEnvTy(Ty<'tcx>),
     RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
     TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),

Diff for: src/librustc/traits/structural_impls.rs

@@ -449,6 +449,7 @@ impl<'tcx> fmt::Display for traits::DomainGoal<'tcx> {
             FromEnv(Implemented(trait_ref)) => write!(fmt, "FromEnv({})", trait_ref),
             FromEnv(ProjectionEq(projection)) => write!(fmt, "FromEnv({})", projection),
             WellFormedTy(ty) => write!(fmt, "WellFormed({})", ty),
+            Normalize(projection) => write!(fmt, "Normalize({})", projection),
             FromEnvTy(ty) => write!(fmt, "FromEnv({})", ty),
             RegionOutlives(predicate) => write!(fmt, "RegionOutlives({})", predicate),
             TypeOutlives(predicate) => write!(fmt, "TypeOutlives({})", predicate),
@@ -537,6 +538,7 @@ EnumTypeFoldableImpl! {
         (traits::DomainGoal::WellFormed)(wc),
         (traits::DomainGoal::FromEnv)(wc),
         (traits::DomainGoal::WellFormedTy)(ty),
+        (traits::DomainGoal::Normalize)(projection),
         (traits::DomainGoal::FromEnvTy)(ty),
         (traits::DomainGoal::RegionOutlives)(predicate),
         (traits::DomainGoal::TypeOutlives)(predicate),

Diff for: src/librustc_traits/lowering.rs

@@ -106,6 +106,7 @@ impl<'tcx> IntoFromEnvGoal for DomainGoal<'tcx> {
             FromEnv(..) |
             WellFormedTy(..) |
             FromEnvTy(..) |
+            Normalize(..) |
             RegionOutlives(..) |
             TypeOutlives(..) => self,
         }
@@ -116,10 +117,20 @@ crate fn program_clauses_for<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefI
     -> Lrc<Vec<Clause<'tcx>>>
 {
     let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
-    let item = tcx.hir.expect_item(node_id);
-    match item.node {
-        hir::ItemTrait(..) => program_clauses_for_trait(tcx, def_id),
-        hir::ItemImpl(..) => program_clauses_for_impl(tcx, def_id),
+    let node = tcx.hir.find(node_id).unwrap();
+    match node {
+        hir::map::Node::NodeItem(item) => match item.node {
+            hir::ItemTrait(..) => program_clauses_for_trait(tcx, def_id),
+            hir::ItemImpl(..) => program_clauses_for_impl(tcx, def_id),
+            _ => Lrc::new(vec![]),
+        }
+        hir::map::Node::NodeImplItem(item) => {
+            if let hir::ImplItemKind::Type(..) = item.node {
+                program_clauses_for_associated_type_value(tcx, def_id)
+            } else {
+                Lrc::new(vec![])
+            }
+        },
 
         // FIXME: other constructions e.g. traits, associated types...
         _ => Lrc::new(vec![]),
@@ -229,6 +240,56 @@ fn program_clauses_for_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId
     Lrc::new(vec![Clause::ForAll(ty::Binder::dummy(clause))])
 }
 
+pub fn program_clauses_for_associated_type_value<'a, 'tcx>(
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    item_id: DefId,
+) -> Lrc<Vec<Clause<'tcx>>> {
+    // Rule Normalize-From-Impl (see rustc guide)
+    //
+    // ```impl<P0..Pn> Trait<A1..An> for A0
+    // {
+    //     type AssocType<Pn+1..Pm> where WC = T;
+    // }```
+    //
+    // ```
+    // forall<P0..Pm> {
+    //   forall<Pn+1..Pm> {
+    //     Normalize(<A0 as Trait<A1..An>>::AssocType<Pn+1..Pm> -> T) :-
+    //       Implemented(A0: Trait<A1..An>) && WC
+    //   }
+    // }
+    // ```
+
+    let item = tcx.associated_item(item_id);
+    debug_assert_eq!(item.kind, ty::AssociatedKind::Type);
+    let impl_id = if let ty::AssociatedItemContainer::ImplContainer(impl_id) = item.container {
+        impl_id
+    } else {
+        bug!()
+    };
+    // `A0 as Trait<A1..An>`
+    let trait_ref = tcx.impl_trait_ref(impl_id).unwrap();
+    // `T`
+    let ty = tcx.type_of(item_id);
+    // `Implemented(A0: Trait<A1..An>)`
+    let trait_implemented = ty::Binder::dummy(ty::TraitPredicate { trait_ref }.lower());
+    // `WC`
+    let item_where_clauses = tcx.predicates_of(item_id).predicates.lower();
+    // `Implemented(A0: Trait<A1..An>) && WC`
+    let mut where_clauses = vec![trait_implemented];
+    where_clauses.extend(item_where_clauses);
+    // `<A0 as Trait<A1..An>>::AssocType<Pn+1..Pm>`
+    let projection_ty = ty::ProjectionTy::from_ref_and_name(tcx, trait_ref, item.name);
+    // `Normalize(<A0 as Trait<A1..An>>::AssocType<Pn+1..Pm> -> T)`
+    let normalize_goal = DomainGoal::Normalize(ty::ProjectionPredicate { projection_ty, ty });
+    // `Normalize(... -> T) :- ...`
+    let clause = ProgramClause {
+        goal: normalize_goal,
+        hypotheses: where_clauses.into_iter().map(|wc| wc.into()).collect(),
+    };
+    Lrc::new(vec![Clause::ForAll(ty::Binder::dummy(clause))])
+}
+
 pub fn dump_program_clauses<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
     if !tcx.features().rustc_attrs {
         return;

Diff for: src/test/ui/chalkify/lower_impl.rs

@@ -15,6 +15,15 @@ trait Foo { }
 #[rustc_dump_program_clauses] //~ ERROR Implemented(T: Foo) :-
 impl<T: 'static> Foo for T where T: Iterator<Item = i32> { }
 
+trait Bar {
+    type Assoc;
+}
+
+impl<T> Bar for T where T: Iterator<Item = i32> {
+    #[rustc_dump_program_clauses] //~ ERROR Normalize(<T as Bar>::Assoc == std::vec::Vec<T>) :-
+    type Assoc = Vec<T>;
+}
+
 fn main() {
     println!("hello");
 }

Diff for: src/test/ui/chalkify/lower_impl.stderr

@@ -4,5 +4,11 @@ error: Implemented(T: Foo) :- ProjectionEq(<T as std::iter::Iterator>::Item == i
 LL | #[rustc_dump_program_clauses] //~ ERROR Implemented(T: Foo) :-
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: Normalize(<T as Bar>::Assoc == std::vec::Vec<T>) :- Implemented(T: Bar).
+  --> $DIR/lower_impl.rs:23:5
+   |
+LL |     #[rustc_dump_program_clauses] //~ ERROR Normalize(<T as Bar>::Assoc == std::vec::Vec<T>) :-
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors