9 files changed, 86 insertions, 40 deletions

diff --git a/crates/hir_ty/src/builder.rs b/crates/hir_ty/src/builder.rs
index 9b2c6975a..791915fe0 100644
--- a/crates/hir_ty/src/builder.rs
+++ b/crates/hir_ty/src/builder.rs
@@ -12,8 +12,8 @@ use smallvec::SmallVec;
 
 use crate::{
     db::HirDatabase, primitive, to_assoc_type_id, to_chalk_trait_id, utils::generics, Binders,
-    CallableSig, FnPointer, FnSig, GenericArg, Interner, ProjectionTy, Substitution, TraitRef, Ty,
-    TyDefId, TyKind, TypeWalk, ValueTyDefId,
+    CallableSig, FnPointer, FnSig, FnSubst, GenericArg, Interner, ProjectionTy, Substitution,
+    TraitRef, Ty, TyDefId, TyKind, TypeWalk, ValueTyDefId,
 };
 
 /// This is a builder for `Ty` or anything that needs a `Substitution`.
@@ -78,9 +78,12 @@ impl TyBuilder<()> {
 
     pub fn fn_ptr(sig: CallableSig) -> Ty {
         TyKind::Function(FnPointer {
-            num_args: sig.params().len(),
+            num_binders: 0,
             sig: FnSig { abi: (), safety: Safety::Safe, variadic: sig.is_varargs },
-            substs: Substitution::from_iter(&Interner, sig.params_and_return.iter().cloned()),
+            substitution: FnSubst(Substitution::from_iter(
+                &Interner,
+                sig.params_and_return.iter().cloned(),
+            )),
         })
         .intern(&Interner)
     }
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 185a2dfc3..a2a7236a8 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -22,8 +22,8 @@ use crate::{
     to_chalk_trait_id,
     traits::{chalk::from_chalk, FnTrait},
     utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, InEnvironment, Interner, ProjectionTyExt,
-    Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyKind,
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
+    ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyKind,
 };
 
 use super::{
@@ -260,9 +260,9 @@ impl<'a> InferenceContext<'a> {
                 };
                 sig_tys.push(ret_ty.clone());
                 let sig_ty = TyKind::Function(FnPointer {
-                    num_args: sig_tys.len() - 1,
+                    num_binders: 0,
                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
-                    substs: Substitution::from_iter(&Interner, sig_tys.clone()),
+                    substitution: FnSubst(Substitution::from_iter(&Interner, sig_tys.clone())),
                 })
                 .intern(&Interner);
                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index c90a16720..2f9523325 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -7,7 +7,7 @@ use ena::unify::{InPlaceUnificationTable, NoError, UnifyKey, UnifyValue};
 
 use super::{DomainGoal, InferenceContext};
 use crate::{
-    AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds, DebruijnIndex, FnPointer,
+    AliasEq, AliasTy, BoundVar, Canonical, CanonicalVarKinds, DebruijnIndex, FnPointer, FnSubst,
     InEnvironment, InferenceVar, Interner, Scalar, Substitution, Ty, TyKind, TypeWalk, WhereClause,
 };
 
@@ -308,8 +308,8 @@ impl InferenceTable {
                 (TyKind::Adt(_, substs1), TyKind::Adt(_, substs2))
                 | (TyKind::FnDef(_, substs1), TyKind::FnDef(_, substs2))
                 | (
-                    TyKind::Function(FnPointer { substs: substs1, .. }),
-                    TyKind::Function(FnPointer { substs: substs2, .. }),
+                    TyKind::Function(FnPointer { substitution: FnSubst(substs1), .. }),
+                    TyKind::Function(FnPointer { substitution: FnSubst(substs2), .. }),
                 )
                 | (TyKind::Tuple(_, substs1), TyKind::Tuple(_, substs2))
                 | (TyKind::OpaqueType(_, substs1), TyKind::OpaqueType(_, substs2))
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index f74b22b58..c3ec12352 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -142,10 +142,11 @@ impl CallableSig {
         CallableSig {
             // FIXME: what to do about lifetime params? -> return PolyFnSig
             params_and_return: fn_ptr
-                .substs
+                .substitution
                 .clone()
                 .shifted_out_to(DebruijnIndex::ONE)
                 .expect("unexpected lifetime vars in fn ptr")
+                .0
                 .interned()
                 .iter()
                 .map(|arg| arg.assert_ty_ref(&Interner).clone())
@@ -239,9 +240,9 @@ impl Ty {
                 mutability == mutability2
             }
             (
-                TyKind::Function(FnPointer { num_args, sig, .. }),
-                TyKind::Function(FnPointer { num_args: num_args2, sig: sig2, .. }),
-            ) => num_args == num_args2 && sig == sig2,
+                TyKind::Function(FnPointer { num_binders, sig, .. }),
+                TyKind::Function(FnPointer { num_binders: num_binders2, sig: sig2, .. }),
+            ) => num_binders == num_binders2 && sig == sig2,
             (TyKind::Tuple(cardinality, _), TyKind::Tuple(cardinality2, _)) => {
                 cardinality == cardinality2
             }
@@ -314,11 +315,11 @@ impl Ty {
         match self.kind(&Interner) {
             TyKind::Adt(_, substs)
             | TyKind::FnDef(_, substs)
-            | TyKind::Function(FnPointer { substs, .. })
             | TyKind::Tuple(_, substs)
             | TyKind::OpaqueType(_, substs)
             | TyKind::AssociatedType(_, substs)
             | TyKind::Closure(.., substs) => Some(substs),
+            TyKind::Function(FnPointer { substitution: substs, .. }) => Some(&substs.0),
             _ => None,
         }
     }
@@ -327,11 +328,11 @@ impl Ty {
         match self.interned_mut() {
             TyKind::Adt(_, substs)
             | TyKind::FnDef(_, substs)
-            | TyKind::Function(FnPointer { substs, .. })
             | TyKind::Tuple(_, substs)
             | TyKind::OpaqueType(_, substs)
             | TyKind::AssociatedType(_, substs)
             | TyKind::Closure(.., substs) => Some(substs),
+            TyKind::Function(FnPointer { substitution: substs, .. }) => Some(&mut substs.0),
             _ => None,
         }
     }
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 6cef8095f..20bb7dd59 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -34,9 +34,9 @@ use crate::{
         variant_data, Generics,
     },
     AliasEq, AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, DynTy, FnPointer, FnSig,
-    ImplTraitId, OpaqueTy, PolyFnSig, ProjectionTy, QuantifiedWhereClause, QuantifiedWhereClauses,
-    ReturnTypeImplTrait, ReturnTypeImplTraits, Substitution, TraitEnvironment, TraitRef, Ty,
-    TyBuilder, TyKind, TypeWalk, WhereClause,
+    FnSubst, ImplTraitId, OpaqueTy, PolyFnSig, ProjectionTy, QuantifiedWhereClause,
+    QuantifiedWhereClauses, ReturnTypeImplTrait, ReturnTypeImplTraits, Substitution,
+    TraitEnvironment, TraitRef, Ty, TyBuilder, TyKind, TypeWalk, WhereClause,
 };
 
 #[derive(Debug)]
@@ -181,9 +181,9 @@ impl<'a> TyLoweringContext<'a> {
                 let substs =
                     Substitution::from_iter(&Interner, params.iter().map(|tr| self.lower_ty(tr)));
                 TyKind::Function(FnPointer {
-                    num_args: substs.len(&Interner) - 1,
+                    num_binders: 0, // FIXME lower `for<'a> fn()` correctly
                     sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
-                    substs,
+                    substitution: FnSubst(substs),
                 })
                 .intern(&Interner)
             }
diff --git a/crates/hir_ty/src/method_resolution.rs b/crates/hir_ty/src/method_resolution.rs
index d6de844a8..6d65d3eb9 100644
--- a/crates/hir_ty/src/method_resolution.rs
+++ b/crates/hir_ty/src/method_resolution.rs
@@ -46,18 +46,18 @@ impl TyFingerprint {
     /// have impls: if we have some `struct S`, we can have an `impl S`, but not
     /// `impl &S`. Hence, this will return `None` for reference types and such.
     pub fn for_impl(ty: &Ty) -> Option<TyFingerprint> {
-        let fp = match *ty.kind(&Interner) {
+        let fp = match ty.kind(&Interner) {
             TyKind::Str => TyFingerprint::Str,
             TyKind::Never => TyFingerprint::Never,
             TyKind::Slice(..) => TyFingerprint::Slice,
             TyKind::Array(..) => TyFingerprint::Array,
-            TyKind::Scalar(scalar) => TyFingerprint::Scalar(scalar),
-            TyKind::Adt(AdtId(adt), _) => TyFingerprint::Adt(adt),
-            TyKind::Tuple(cardinality, _) => TyFingerprint::Tuple(cardinality),
-            TyKind::Raw(mutability, ..) => TyFingerprint::RawPtr(mutability),
-            TyKind::Foreign(alias_id, ..) => TyFingerprint::ForeignType(alias_id),
-            TyKind::Function(FnPointer { num_args, sig, .. }) => {
-                TyFingerprint::FnPtr(num_args, sig)
+            TyKind::Scalar(scalar) => TyFingerprint::Scalar(*scalar),
+            TyKind::Adt(AdtId(adt), _) => TyFingerprint::Adt(*adt),
+            TyKind::Tuple(cardinality, _) => TyFingerprint::Tuple(*cardinality),
+            TyKind::Raw(mutability, ..) => TyFingerprint::RawPtr(*mutability),
+            TyKind::Foreign(alias_id, ..) => TyFingerprint::ForeignType(*alias_id),
+            TyKind::Function(FnPointer { sig, substitution: substs, .. }) => {
+                TyFingerprint::FnPtr(substs.0.len(&Interner) - 1, *sig)
             }
             TyKind::Dyn(_) => ty.dyn_trait().map(|trait_| TyFingerprint::Dyn(trait_))?,
             _ => return None,
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 9f10b889f..13d8d1111 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -24,8 +24,8 @@ impl ToChalk for Ty {
         match self.into_inner() {
             TyKind::Ref(m, ty) => ref_to_chalk(db, m, ty),
             TyKind::Array(ty) => array_to_chalk(db, ty),
-            TyKind::Function(FnPointer { sig, substs, .. }) => {
-                let substitution = chalk_ir::FnSubst(substs.to_chalk(db).shifted_in(&Interner));
+            TyKind::Function(FnPointer { sig, substitution: substs, .. }) => {
+                let substitution = chalk_ir::FnSubst(substs.0.to_chalk(db).shifted_in(&Interner));
                 chalk_ir::TyKind::Function(chalk_ir::FnPointer {
                     num_binders: 0,
                     sig,
@@ -132,11 +132,11 @@ impl ToChalk for Ty {
                 ..
             }) => {
                 assert_eq!(num_binders, 0);
-                let substs: Substitution = from_chalk(
+                let substs = crate::FnSubst(from_chalk(
                     db,
                     substitution.0.shifted_out(&Interner).expect("fn ptr should have no binders"),
-                );
-                TyKind::Function(FnPointer { num_args: (substs.len(&Interner) - 1), sig, substs })
+                ));
+                TyKind::Function(FnPointer { num_binders, sig, substitution: substs })
             }
             chalk_ir::TyKind::BoundVar(idx) => TyKind::BoundVar(idx),
             chalk_ir::TyKind::InferenceVar(_iv, _kind) => TyKind::Error,
diff --git a/crates/hir_ty/src/types.rs b/crates/hir_ty/src/types.rs
index 4a626d5e7..d4e07a6b8 100644
--- a/crates/hir_ty/src/types.rs
+++ b/crates/hir_ty/src/types.rs
@@ -11,7 +11,7 @@ use smallvec::SmallVec;
 
 use crate::{
     AssocTypeId, CanonicalVarKinds, ChalkTraitId, ClosureId, FnDefId, FnSig, ForeignDefId,
-    InferenceVar, Interner, OpaqueTyId, PlaceholderIndex, TypeWalk, VariableKinds,
+    InferenceVar, Interner, OpaqueTyId, PlaceholderIndex, TypeWalk, VariableKind, VariableKinds,
 };
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
@@ -43,9 +43,36 @@ pub struct DynTy {
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct FnPointer {
-    pub num_args: usize,
+    pub num_binders: usize,
     pub sig: FnSig,
-    pub substs: Substitution,
+    pub substitution: FnSubst,
+}
+/// A wrapper for the substs on a Fn.
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
+pub struct FnSubst(pub Substitution);
+
+impl FnPointer {
+    /// Represent the current `Fn` as if it was wrapped in `Binders`
+    pub fn into_binders(self, interner: &Interner) -> Binders<FnSubst> {
+        Binders::new(
+            VariableKinds::from_iter(
+                interner,
+                (0..self.num_binders).map(|_| VariableKind::Lifetime),
+            ),
+            self.substitution,
+        )
+    }
+
+    /// Represent the current `Fn` as if it was wrapped in `Binders`
+    pub fn as_binders(&self, interner: &Interner) -> Binders<&FnSubst> {
+        Binders::new(
+            VariableKinds::from_iter(
+                interner,
+                (0..self.num_binders).map(|_| VariableKind::Lifetime),
+            ),
+            &self.substitution,
+        )
+    }
 }
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
diff --git a/crates/hir_ty/src/walk.rs b/crates/hir_ty/src/walk.rs
index b85e6ab4d..963eb12c8 100644
--- a/crates/hir_ty/src/walk.rs
+++ b/crates/hir_ty/src/walk.rs
@@ -6,8 +6,9 @@ use std::mem;
 use chalk_ir::DebruijnIndex;
 
 use crate::{
-    utils::make_mut_slice, AliasEq, AliasTy, Binders, CallableSig, GenericArg, GenericArgData,
-    Interner, OpaqueTy, ProjectionTy, Substitution, TraitRef, Ty, TyKind, WhereClause,
+    utils::make_mut_slice, AliasEq, AliasTy, Binders, CallableSig, FnSubst, GenericArg,
+    GenericArgData, Interner, OpaqueTy, ProjectionTy, Substitution, TraitRef, Ty, TyKind,
+    WhereClause,
 };
 
 /// This allows walking structures that contain types to do something with those
@@ -381,3 +382,17 @@ impl TypeWalk for AliasEq {
         }
     }
 }
+
+impl TypeWalk for FnSubst {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
+        self.0.walk(f)
+    }
+
+    fn walk_mut_binders(
+        &mut self,
+        f: &mut impl FnMut(&mut Ty, DebruijnIndex),
+        binders: DebruijnIndex,
+    ) {
+        self.0.walk_mut_binders(f, binders)
+    }
+}