Added `mir::UserTypeProjection`, a stub for a structure that projects *into* a given UserTypeAnnotation.

(That is, it will pull out some component type held or referenced by
the type annotation.)

Note: this still needs to actually do projection itself. That comes in
a later commit

3 files changed, 36 insertions, 6 deletions

diff --git a/src/librustc/ich/impls_mir.rs b/src/librustc/ich/impls_mir.rs
index 4f68569c600..94b85247bb8 100644
--- a/src/librustc/ich/impls_mir.rs
+++ b/src/librustc/ich/impls_mir.rs
@@ -606,3 +606,5 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for mir::UserTypeAnnotation<
         }
     }
 }
+
+impl_stable_hash_for!(struct mir::UserTypeProjection<'tcx> { base });
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index 7c3d4713572..d2f67a74420 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -710,7 +710,7 @@ pub struct LocalDecl<'tcx> {
     /// e.g. via `let x: T`, then we carry that type here. The MIR
     /// borrow checker needs this information since it can affect
     /// region inference.
-    pub user_ty: Option<(UserTypeAnnotation<'tcx>, Span)>,
+    pub user_ty: Option<(UserTypeProjection<'tcx>, Span)>,
 
     /// Name of the local, used in debuginfo and pretty-printing.
     ///
@@ -1741,7 +1741,7 @@ pub enum StatementKind<'tcx> {
     /// - `Contravariant` -- requires that `T_y :> T`
     /// - `Invariant` -- requires that `T_y == T`
     /// - `Bivariant` -- no effect
-    AscribeUserType(Place<'tcx>, ty::Variance, Box<UserTypeAnnotation<'tcx>>),
+    AscribeUserType(Place<'tcx>, ty::Variance, Box<UserTypeProjection<'tcx>>),
 
     /// No-op. Useful for deleting instructions without affecting statement indices.
     Nop,
@@ -2449,6 +2449,17 @@ EnumLiftImpl! {
     }
 }
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
+pub struct UserTypeProjection<'tcx> {
+    pub base: UserTypeAnnotation<'tcx>,
+}
+
+BraceStructTypeFoldableImpl! {
+    impl<'tcx> TypeFoldable<'tcx> for UserTypeProjection<'tcx> {
+        base
+    }
+}
+
 newtype_index! {
     pub struct Promoted {
         DEBUG_FORMAT = "promoted[{}]"
diff --git a/src/librustc/mir/visit.rs b/src/librustc/mir/visit.rs
index 1a879ce5f7b..acca7ddcd3f 100644
--- a/src/librustc/mir/visit.rs
+++ b/src/librustc/mir/visit.rs
@@ -147,7 +147,7 @@ macro_rules! make_mir_visitor {
             fn visit_ascribe_user_ty(&mut self,
                                      place: & $($mutability)* Place<'tcx>,
                                      variance: & $($mutability)* ty::Variance,
-                                     user_ty: & $($mutability)* UserTypeAnnotation<'tcx>,
+                                     user_ty: & $($mutability)* UserTypeProjection<'tcx>,
                                      location: Location) {
                 self.super_ascribe_user_ty(place, variance, user_ty, location);
             }
@@ -213,6 +213,13 @@ macro_rules! make_mir_visitor {
                 self.super_ty(ty);
             }
 
+            fn visit_user_type_projection(
+                &mut self,
+                ty: & $($mutability)* UserTypeProjection<'tcx>,
+            ) {
+                self.super_user_type_projection(ty);
+            }
+
             fn visit_user_type_annotation(
                 &mut self,
                 ty: & $($mutability)* UserTypeAnnotation<'tcx>,
@@ -639,10 +646,10 @@ macro_rules! make_mir_visitor {
             fn super_ascribe_user_ty(&mut self,
                                      place: & $($mutability)* Place<'tcx>,
                                      _variance: & $($mutability)* ty::Variance,
-                                     user_ty: & $($mutability)* UserTypeAnnotation<'tcx>,
+                                     user_ty: & $($mutability)* UserTypeProjection<'tcx>,
                                      location: Location) {
                 self.visit_place(place, PlaceContext::Validate, location);
-                self.visit_user_type_annotation(user_ty);
+                self.visit_user_type_projection(user_ty);
             }
 
             fn super_place(&mut self,
@@ -737,7 +744,7 @@ macro_rules! make_mir_visitor {
                     source_info: *source_info,
                 });
                 if let Some((user_ty, _)) = user_ty {
-                    self.visit_user_type_annotation(user_ty);
+                    self.visit_user_type_projection(user_ty);
                 }
                 self.visit_source_info(source_info);
                 self.visit_source_scope(visibility_scope);
@@ -784,6 +791,16 @@ macro_rules! make_mir_visitor {
                 self.visit_source_scope(scope);
             }
 
+            fn super_user_type_projection(
+                &mut self,
+                ty: & $($mutability)* UserTypeProjection<'tcx>,
+            ) {
+                let UserTypeProjection {
+                    ref $($mutability)* base,
+                } = *ty;
+                self.visit_user_type_annotation(base)
+            }
+
             fn super_user_type_annotation(
                 &mut self,
                 _ty: & $($mutability)* UserTypeAnnotation<'tcx>,