Lower type ascriptions to HAIR and MIR

src/librustc_mir/build/expr/as_place.rs

@@ -16,6 +16,7 @@ use build::{BlockAnd, BlockAndExtension, Builder};
 use hair::*;
 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
 use rustc::mir::*;
+use rustc::ty::Variance;
 
 use rustc_data_structures::indexed_vec::Idx;
 
@@ -136,6 +137,40 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 ty: expr.ty,
             }))),
 
+            ExprKind::PlaceTypeAscription { source, user_ty } => {
+                let place = unpack!(block = this.as_place(block, source));
+                this.cfg.push(
+                    block,
+                    Statement {
+                        source_info,
+                        kind: StatementKind::AscribeUserType(
+                            place.clone(),
+                            Variance::Invariant,
+                            user_ty,
+                        ),
+                    },
+                );
+                block.and(place)
+            }
+            ExprKind::ValueTypeAscription { source, user_ty } => {
+                let source = this.hir.mirror(source);
+                let temp = unpack!(
+                    block = this.as_temp(block, source.temp_lifetime, source, mutability)
+                );
+                this.cfg.push(
+                    block,
+                    Statement {
+                        source_info,
+                        kind: StatementKind::AscribeUserType(
+                            Place::Local(temp.clone()),
+                            Variance::Invariant,
+                            user_ty,
+                        ),
+                    },
+                );
+                block.and(Place::Local(temp))
+            }
+
             ExprKind::Array { .. }
             | ExprKind::Tuple { .. }
             | ExprKind::Adt { .. }

src/librustc_mir/build/expr/as_rvalue.rs

@@ -386,7 +386,9 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             | ExprKind::Continue { .. }
             | ExprKind::Return { .. }
             | ExprKind::InlineAsm { .. }
-            | ExprKind::StaticRef { .. } => {
+            | ExprKind::StaticRef { .. }
+            | ExprKind::PlaceTypeAscription { .. }
+            | ExprKind::ValueTypeAscription { .. } => {
                 // these do not have corresponding `Rvalue` variants,
                 // so make an operand and then return that
                 debug_assert!(match Category::of(&expr.kind) {

src/librustc_mir/build/expr/category.rs

@@ -50,7 +50,9 @@ impl Category {
             | ExprKind::Index { .. }
             | ExprKind::SelfRef
             | ExprKind::VarRef { .. }
-            | ExprKind::StaticRef { .. } => Some(Category::Place),
+            | ExprKind::StaticRef { .. }
+            | ExprKind::PlaceTypeAscription { .. }
+            | ExprKind::ValueTypeAscription { .. } => Some(Category::Place),
 
             ExprKind::LogicalOp { .. }
             | ExprKind::If { .. }

src/librustc_mir/build/expr/into.rs

@@ -391,7 +391,9 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             | ExprKind::Adt { .. }
             | ExprKind::Closure { .. }
             | ExprKind::Literal { .. }
-            | ExprKind::Yield { .. } => {
+            | ExprKind::Yield { .. }
+            | ExprKind::PlaceTypeAscription { .. }
+            | ExprKind::ValueTypeAscription { .. } => {
                 debug_assert!(match Category::of(&expr.kind).unwrap() {
                     Category::Rvalue(RvalueFunc::Into) => false,
                     _ => true,

src/librustc_mir/hair/cx/expr.rs

@@ -718,7 +718,23 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                 ExprKind::Cast { source }
             }
         }
-        hir::ExprKind::Type(ref source, _) => return source.make_mirror(cx),
+        hir::ExprKind::Type(ref source, ref ty) => {
+            let user_provided_tys = cx.tables.user_provided_tys();
+            let user_ty = *user_provided_tys
+                .get(ty.hir_id)
+                .expect(&format!("{:?} not found in user_provided_tys, source: {:?}", ty, source));
+            if source.is_place_expr() {
+                ExprKind::PlaceTypeAscription {
+                    source: source.to_ref(),
+                    user_ty,
+                }
+            } else {
+                ExprKind::ValueTypeAscription {
+                    source: source.to_ref(),
+                    user_ty,
+                }
+            }
+        }
         hir::ExprKind::Box(ref value) => {
             ExprKind::Box {
                 value: value.to_ref(),

src/librustc_mir/hair/mod.rs

@@ -268,6 +268,16 @@ pub enum ExprKind<'tcx> {
         fields: Vec<FieldExprRef<'tcx>>,
         base: Option<FruInfo<'tcx>>
     },
+    PlaceTypeAscription {
+        source: ExprRef<'tcx>,
+        /// Type that the user gave to this expression
+        user_ty: CanonicalTy<'tcx>,
+    },
+    ValueTypeAscription {
+        source: ExprRef<'tcx>,
+        /// Type that the user gave to this expression
+        user_ty: CanonicalTy<'tcx>,
+    },
     Closure {
         closure_id: DefId,
         substs: UpvarSubsts<'tcx>,

src/librustc_typeck/check/mod.rs

@@ -4118,6 +4118,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             hir::ExprKind::Type(ref e, ref t) => {
                 let ty = self.to_ty(&t);
                 self.check_expr_eq_type(&e, ty);
+                let c_ty = self.infcx.canonicalize_response(&ty);
+                self.tables.borrow_mut().user_provided_tys_mut().insert(t.hir_id, c_ty);
                 ty
             }
             hir::ExprKind::Array(ref args) => {