Add support for quantified bounds on GATs

Author: scalexm

chalk-parse/src/ast.rs

@@ -62,7 +62,7 @@ pub struct TraitFlags {
 pub struct AssocTyDefn {
     pub name: Identifier,
     pub parameter_kinds: Vec<ParameterKind>,
-    pub bounds: Vec<InlineBound>,
+    pub bounds: Vec<QuantifiedInlineBound>,
     pub where_clauses: Vec<QuantifiedWhereClause>,
 }
 
@@ -85,6 +85,12 @@ pub enum InlineBound {
     ProjectionEqBound(ProjectionEqBound),
 }
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct QuantifiedInlineBound {
+    pub parameter_kinds: Vec<ParameterKind>,
+    pub bound: InlineBound,
+}
+
 #[derive(Clone, PartialEq, Eq, Debug)]
 /// Represents a trait bound on e.g. a type or type parameter.
 /// Does not know anything about what it's binding.

chalk-parse/src/parser.lalrpop

@@ -74,7 +74,7 @@ TraitDefn: TraitDefn = {
 };
 
 AssocTyDefn: AssocTyDefn = {
-    "type" <name:Id> <p:Angle<ParameterKind>> <b:(":" <Plus<InlineBound>>)?>
+    "type" <name:Id> <p:Angle<ParameterKind>> <b:(":" <Plus<QuantifiedInlineBound>>)?>
         <w:QuantifiedWhereClauses> ";" =>
     {
         AssocTyDefn {
@@ -114,6 +114,18 @@ ProjectionEqBound: ProjectionEqBound = {
     }
 };
 
+QuantifiedInlineBound: QuantifiedInlineBound = {
+    <b:InlineBound> => QuantifiedInlineBound {
+        parameter_kinds: vec![],
+        bound: b,
+    },
+
+    "forall" "<" <pk:Comma<ParameterKind>> ">" <b:InlineBound> => QuantifiedInlineBound {
+        parameter_kinds: pk,
+        bound: b,
+    },
+};
+
 Impl: Impl = {
     "impl" <p:Angle<ParameterKind>> <mark:"!"?> <t:Id> <a:Angle<Parameter>> "for" <s:Ty>
         <w:QuantifiedWhereClauses> "{" <assoc:AssocTyValue*> "}" =>

src/ir.rs

@@ -268,19 +268,34 @@ pub enum InlineBound {
     ProjectionEqBound(ProjectionEqBound),
 }
 
+pub type QuantifiedInlineBound = Binders<InlineBound>;
+
 impl InlineBound {
     /// Applies the `InlineBound` to `self_ty` and lowers to a [`DomainGoal`].
     ///
     /// Because an `InlineBound` does not know anything about what it's binding,
     /// you must provide that type as `self_ty`.
-    crate fn into_where_clauses(&self, self_ty: Ty) -> Vec<WhereClause> {
+    fn into_where_clauses(&self, self_ty: Ty) -> Vec<WhereClause> {
         match self {
             InlineBound::TraitBound(b) => b.into_where_clauses(self_ty),
             InlineBound::ProjectionEqBound(b) => b.into_where_clauses(self_ty),
         }
     }
 }
 
+impl QuantifiedInlineBound {
+    crate fn into_where_clauses(&self, self_ty: Ty) -> Vec<QuantifiedWhereClause> {
+        let self_ty = self_ty.up_shift(self.binders.len());
+        self.value.into_where_clauses(self_ty).into_iter().map(|wc| {
+            Binders {
+                binders: self.binders.clone(),
+                value: wc,
+            }
+        }).collect()
+    }
+}
+
+
 /// Represents a trait bound on e.g. a type or type parameter.
 /// Does not know anything about what it's binding.
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -290,7 +305,7 @@ pub struct TraitBound {
 }
 
 impl TraitBound {
-    crate fn into_where_clauses(&self, self_ty: Ty) -> Vec<WhereClause> {
+    fn into_where_clauses(&self, self_ty: Ty) -> Vec<WhereClause> {
         let trait_ref = self.as_trait_ref(self_ty);
         vec![WhereClause::Implemented(trait_ref)]
     }
@@ -303,7 +318,6 @@ impl TraitBound {
         }
     }
 }
-
 /// Represents a projection equality bound on e.g. a type or type parameter.
 /// Does not know anything about what it's binding.
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -316,7 +330,7 @@ pub struct ProjectionEqBound {
 }
 
 impl ProjectionEqBound {
-    crate fn into_where_clauses(&self, self_ty: Ty) -> Vec<WhereClause> {
+    fn into_where_clauses(&self, self_ty: Ty) -> Vec<WhereClause> {
         let trait_ref = self.trait_bound.as_trait_ref(self_ty);
 
         let mut parameters = self.parameters.clone();
@@ -354,7 +368,7 @@ pub struct AssociatedTyDatum {
     ///
     /// These must be proven by the implementer, for all possible parameters that
     /// would result in a well-formed projection.
-    crate bounds: Vec<InlineBound>,
+    crate bounds: Vec<QuantifiedInlineBound>,
 
     /// Where clauses that must hold for the projection to be well-formed.
     crate where_clauses: Vec<QuantifiedWhereClause>,
@@ -366,7 +380,7 @@ impl AssociatedTyDatum {
     /// ```notrust
     /// Implemented(<?0 as Foo>::Item<?1>: Sized)
     /// ```
-    crate fn bounds_on_self(&self) -> Vec<WhereClause> {
+    crate fn bounds_on_self(&self) -> Vec<QuantifiedWhereClause> {
         let parameters = self.parameter_kinds
                              .anonymize()
                              .iter()

src/ir/lowering.rs

@@ -412,17 +412,11 @@ impl LowerWhereClauses for Impl {
     }
 }
 
-trait LowerWhereClauseVec<T> {
-    fn lower(&self, env: &Env) -> Result<Vec<T>>;
+trait LowerWhereClauseVec {
+    fn lower(&self, env: &Env) -> Result<Vec<ir::QuantifiedWhereClause>>;
 }
 
-impl LowerWhereClauseVec<ir::WhereClause> for [WhereClause] {
-    fn lower(&self, env: &Env) -> Result<Vec<ir::WhereClause>> {
-        self.iter().flat_map(|wc| wc.lower(env).apply_result()).collect()
-    }
-}
-
-impl LowerWhereClauseVec<ir::QuantifiedWhereClause> for [QuantifiedWhereClause] {
+impl LowerWhereClauseVec for [QuantifiedWhereClause] {
     fn lower(&self, env: &Env) -> Result<Vec<ir::QuantifiedWhereClause>> {
         self.iter()
             .flat_map(|wc| match wc.lower(env) {
@@ -712,12 +706,26 @@ impl LowerInlineBound for InlineBound {
     }
 }
 
-trait LowerInlineBounds {
-    fn lower(&self, env: &Env) -> Result<Vec<ir::InlineBound>>;
+trait LowerQuantifiedInlineBound {
+    fn lower(&self, env: &Env) -> Result<ir::QuantifiedInlineBound>;
+}
+
+impl LowerQuantifiedInlineBound for QuantifiedInlineBound {
+    fn lower(&self, env: &Env) -> Result<ir::QuantifiedInlineBound> {
+        let parameter_kinds = self.parameter_kinds.iter().map(|pk| pk.lower());
+        let binders = env.in_binders(parameter_kinds, |env| {
+            Ok(self.bound.lower(env)?)
+        })?;
+        Ok(binders)
+    }
+}
+
+trait LowerQuantifiedInlineBoundVec {
+    fn lower(&self, env: &Env) -> Result<Vec<ir::QuantifiedInlineBound>>;
 }
 
-impl LowerInlineBounds for Vec<InlineBound> {
-    fn lower(&self, env: &Env) -> Result<Vec<ir::InlineBound>> {
+impl LowerQuantifiedInlineBoundVec for [QuantifiedInlineBound] {
+    fn lower(&self, env: &Env) -> Result<Vec<ir::QuantifiedInlineBound>> {
         self.iter()
             .map(|b| b.lower(env))
             .collect()

src/ir/lowering/test.rs

@@ -354,6 +354,21 @@ fn gat_parse() {
     }
 }
 
+#[test]
+fn gat_higher_ranked_bound() {
+    lowering_success! {
+        program {
+            trait Fn<T> {}
+            trait Ref<'a, T> {}
+            trait Sized {}
+
+            trait Foo {
+                type Item<T>: forall<'a> Fn<Ref<'a, T>> + Sized;
+            }
+        }
+    }
+}
+
 #[test]
 fn duplicate_parameters() {
     lowering_error! {
@@ -377,6 +392,19 @@ fn duplicate_parameters() {
             "duplicate parameters"
         }
     }
+
+    lowering_error! {
+        program {
+            trait Fn<T> {}
+            trait Ref<'a, T> {}
+
+            trait Foo<'a> {
+                type Item<T>: forall<'a> Fn<Ref<'a, T>>;
+            }
+        } error_msg {
+            "duplicate parameters"
+        }
+    }
 }
 
 #[test]

src/rules.rs

@@ -614,12 +614,14 @@ impl AssociatedTyDatum {
         //        FromEnv(<T as Foo>::Assoc: Bounds) :- FromEnv(Self: Foo)
         //    }
         clauses.extend(self.bounds_on_self().into_iter().map(|bound| {
+            // Same as above in case of higher-ranked inline bounds.
+            let shift = bound.binders.len();
             Binders {
-                binders: binders.clone(),
+                binders: bound.binders.iter().chain(binders.iter()).cloned().collect(),
                 value: ProgramClauseImplication {
-                    consequence: bound.into_from_env_goal(),
+                    consequence: bound.value.clone().into_from_env_goal(),
                     conditions: vec![
-                        FromEnv::Trait(trait_ref.clone()).cast()
+                        FromEnv::Trait(trait_ref.clone()).up_shift(shift).cast()
                     ],
                 }
             }.cast()

src/rules/wf.rs

@@ -216,7 +216,8 @@ impl WfSolver {
 
             let wf_goals =
                 input_types.into_iter()
-                           .map(|ty| DomainGoal::WellFormed(WellFormed::Ty(ty)));
+                           .map(|ty| DomainGoal::WellFormed(WellFormed::Ty(ty)))
+                           .casted();
 
             let trait_ref = trait_ref.up_shift(assoc_ty.value.binders.len());
 
@@ -233,9 +234,10 @@ impl WfSolver {
                 bounds.iter()
                       .map(|b| Subst::apply(&all_parameters, b))
                       .flat_map(|b| b.into_where_clauses(assoc_ty.value.value.ty.clone()))
-                      .map(|g| g.into_well_formed_goal());
+                      .map(|wc| wc.map(|bound| bound.into_well_formed_goal()))
+                      .casted();
 
-            let goals = wf_goals.chain(bound_goals).casted();
+            let goals = wf_goals.chain(bound_goals);
             let goal = match goals.fold1(|goal, leaf| Goal::And(Box::new(goal), Box::new(leaf))) {
                 Some(goal) => goal,
                 None => return None,

src/rules/wf/test.rs

@@ -519,3 +519,45 @@ fn higher_ranked_cyclic_requirements() {
         }
     }
 }
+
+#[test]
+fn higher_ranked_inline_bound_on_gat() {
+    lowering_success! {
+        program {
+            trait Fn<T> { }
+            struct Ref<'a, T> { }
+            struct i32 {}
+
+            struct fn<T> { }
+
+            impl<'a, T> Fn<Ref<'a, T>> for for<'b> fn<Ref<'b, T>> { }
+
+            trait Bar {
+                type Item<T>: forall<'a> Fn<Ref<'a, T>>;
+            }
+
+            impl Bar for i32 {
+                type Item<T> = for<'a> fn<Ref<'a, T>>;
+            }
+        }
+    }
+
+    lowering_error! {
+        program {
+            trait Fn<T, U> { }
+            struct i32 {}
+
+            struct fn<T, U> { }
+
+            trait Bar {
+                type Item<T>: forall<U> Fn<T, U>;
+            }
+
+            impl Bar for i32 {
+                type Item<T> = fn<T, i32>;
+            }
+        } error_msg {
+            "trait impl for \"Bar\" does not meet well-formedness requirements"
+        }
+    }
+}

src/solve/test.rs

@@ -798,6 +798,30 @@ fn gat_implied_bounds() {
             "No possible solution"
         }
     }
+
+    test! {
+        program {
+            trait Fn<T> { }
+            struct Ref<'a, T> { }
+            trait Sized { }
+
+            trait Foo {
+                type Item<T>: forall<'a> Fn<Ref<'a, T>> + Sized;
+            }
+        }
+
+        goal {
+            forall<Type> {
+                if (Type: Foo) {
+                    forall<'a, T> {
+                        <Type as Foo>::Item<T>: Fn<Ref<'a, T>>
+                    }
+                }
+            }
+        } yields {
+            "Unique"
+        }
+    }
 }
 
 #[test]