[NLL] Clean up handling of type annotations

src/librustc/ich/impls_ty.rs

@@ -1242,7 +1242,7 @@ impl_stable_hash_for!(
 
 impl_stable_hash_for!(
     struct ty::CanonicalUserTypeAnnotation<'tcx> {
-        user_ty, span
+        user_ty, span, inferred_ty
     }
 );
 

src/librustc/mir/tcx.rs

@@ -75,21 +75,20 @@ impl<'a, 'gcx, 'tcx> PlaceTy<'tcx> {
                          elem: &PlaceElem<'tcx>)
                          -> PlaceTy<'tcx>
     {
-        self.projection_ty_core(tcx, elem, |_, _, ty| -> Result<Ty<'tcx>, ()> { Ok(ty) })
-            .unwrap()
+        self.projection_ty_core(tcx, elem, |_, _, ty| ty)
     }
 
     /// `place_ty.projection_ty_core(tcx, elem, |...| { ... })`
     /// projects `place_ty` onto `elem`, returning the appropriate
     /// `Ty` or downcast variant corresponding to that projection.
     /// The `handle_field` callback must map a `Field` to its `Ty`,
     /// (which should be trivial when `T` = `Ty`).
-    pub fn projection_ty_core<V, T, E>(
+    pub fn projection_ty_core<V, T>(
         self,
         tcx: TyCtxt<'a, 'gcx, 'tcx>,
         elem: &ProjectionElem<'tcx, V, T>,
-        mut handle_field: impl FnMut(&Self, &Field, &T) -> Result<Ty<'tcx>, E>)
-        -> Result<PlaceTy<'tcx>, E>
+        mut handle_field: impl FnMut(&Self, &Field, &T) -> Ty<'tcx>)
+        -> PlaceTy<'tcx>
     where
         V: ::std::fmt::Debug, T: ::std::fmt::Debug
     {
@@ -140,10 +139,10 @@ impl<'a, 'gcx, 'tcx> PlaceTy<'tcx> {
                     }
                 },
             ProjectionElem::Field(ref f, ref fty) =>
-                PlaceTy::Ty { ty: handle_field(&self, f, fty)? },
+                PlaceTy::Ty { ty: handle_field(&self, f, fty) },
         };
         debug!("projection_ty self: {:?} elem: {:?} yields: {:?}", self, elem, answer);
-        Ok(answer)
+        answer
     }
 }
 

src/librustc/mir/visit.rs

@@ -887,6 +887,7 @@ macro_rules! make_mir_visitor {
                 ty: & $($mutability)* CanonicalUserTypeAnnotation<'tcx>,
             ) {
                 self.visit_span(& $($mutability)* ty.span);
+                self.visit_ty(& $($mutability)* ty.inferred_ty, TyContext::UserTy(ty.span));
             }
 
             fn super_ty(&mut self, _ty: & $($mutability)* Ty<'tcx>) {
@@ -967,6 +968,9 @@ pub enum TyContext {
         source_info: SourceInfo,
     },
 
+    /// The inferred type of a user type annotation.
+    UserTy(Span),
+
     /// The return type of the function.
     ReturnTy(SourceInfo),
 

src/librustc/traits/query/type_op/ascribe_user_type.rs

@@ -1,28 +1,23 @@
 use infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
 use traits::query::Fallible;
 use hir::def_id::DefId;
-use mir::ProjectionKind;
-use ty::{self, ParamEnvAnd, Ty, TyCtxt};
+use ty::{ParamEnvAnd, Ty, TyCtxt};
 use ty::subst::UserSubsts;
 
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub struct AscribeUserType<'tcx> {
     pub mir_ty: Ty<'tcx>,
-    pub variance: ty::Variance,
     pub def_id: DefId,
     pub user_substs: UserSubsts<'tcx>,
-    pub projs: &'tcx ty::List<ProjectionKind<'tcx>>,
 }
 
 impl<'tcx> AscribeUserType<'tcx> {
     pub fn new(
         mir_ty: Ty<'tcx>,
-        variance: ty::Variance,
         def_id: DefId,
         user_substs: UserSubsts<'tcx>,
-        projs: &'tcx ty::List<ProjectionKind<'tcx>>,
     ) -> Self {
-        Self { mir_ty, variance, def_id, user_substs, projs }
+        Self { mir_ty,  def_id, user_substs }
     }
 }
 
@@ -52,19 +47,19 @@ impl<'gcx: 'tcx, 'tcx> super::QueryTypeOp<'gcx, 'tcx> for AscribeUserType<'tcx>
 
 BraceStructTypeFoldableImpl! {
     impl<'tcx> TypeFoldable<'tcx> for AscribeUserType<'tcx> {
-        mir_ty, variance, def_id, user_substs, projs
+        mir_ty, def_id, user_substs
     }
 }
 
 BraceStructLiftImpl! {
     impl<'a, 'tcx> Lift<'tcx> for AscribeUserType<'a> {
         type Lifted = AscribeUserType<'tcx>;
-        mir_ty, variance, def_id, user_substs, projs
+        mir_ty, def_id, user_substs
     }
 }
 
 impl_stable_hash_for! {
     struct AscribeUserType<'tcx> {
-        mir_ty, variance, def_id, user_substs, projs
+        mir_ty, def_id, user_substs
     }
 }

src/librustc/ty/context.rs

@@ -813,18 +813,19 @@ pub type CanonicalUserTypeAnnotations<'tcx> =
 pub struct CanonicalUserTypeAnnotation<'tcx> {
     pub user_ty: CanonicalUserType<'tcx>,
     pub span: Span,
+    pub inferred_ty: Ty<'tcx>,
 }
 
 BraceStructTypeFoldableImpl! {
     impl<'tcx> TypeFoldable<'tcx> for CanonicalUserTypeAnnotation<'tcx> {
-        user_ty, span
+        user_ty, span, inferred_ty
     }
 }
 
 BraceStructLiftImpl! {
     impl<'a, 'tcx> Lift<'tcx> for CanonicalUserTypeAnnotation<'a> {
         type Lifted = CanonicalUserTypeAnnotation<'tcx>;
-        user_ty, span
+        user_ty, span, inferred_ty
     }
 }
 

src/librustc_mir/borrow_check/nll/constraint_generation.rs

@@ -7,7 +7,7 @@ use rustc::infer::InferCtxt;
 use rustc::mir::visit::TyContext;
 use rustc::mir::visit::Visitor;
 use rustc::mir::{BasicBlock, BasicBlockData, Location, Mir, Place, Rvalue};
-use rustc::mir::{Statement, Terminator};
+use rustc::mir::{SourceInfo, Statement, Terminator};
 use rustc::mir::UserTypeProjection;
 use rustc::ty::fold::TypeFoldable;
 use rustc::ty::subst::Substs;
@@ -66,11 +66,12 @@ impl<'cg, 'cx, 'gcx, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'cx, 'gcx
     /// call. Make them live at the location where they appear.
     fn visit_ty(&mut self, ty: &ty::Ty<'tcx>, ty_context: TyContext) {
         match ty_context {
-            TyContext::ReturnTy(source_info)
-            | TyContext::YieldTy(source_info)
-            | TyContext::LocalDecl { source_info, .. } => {
+            TyContext::ReturnTy(SourceInfo { span, .. })
+            | TyContext::YieldTy(SourceInfo { span, .. })
+            | TyContext::UserTy(span)
+            | TyContext::LocalDecl { source_info: SourceInfo { span, .. }, .. } => {
                 span_bug!(
-                    source_info.span,
+                    span,
                     "should not be visiting outside of the CFG: {:?}",
                     ty_context
                 );

src/librustc_mir/borrow_check/nll/renumber.rs

@@ -1,8 +1,5 @@
 use rustc::ty::subst::Substs;
-use rustc::ty::{
-    self, ClosureSubsts, GeneratorSubsts, Ty, TypeFoldable,
-    UserTypeAnnotationIndex, CanonicalUserTypeAnnotation
-};
+use rustc::ty::{self, ClosureSubsts, GeneratorSubsts, Ty, TypeFoldable};
 use rustc::mir::{Location, Mir};
 use rustc::mir::visit::{MutVisitor, TyContext};
 use rustc::infer::{InferCtxt, NLLRegionVariableOrigin};
@@ -58,18 +55,6 @@ impl<'a, 'gcx, 'tcx> MutVisitor<'tcx> for NLLVisitor<'a, 'gcx, 'tcx> {
         debug!("visit_ty: ty={:?}", ty);
     }
 
-    fn visit_user_type_annotation(
-        &mut self,
-        _index: UserTypeAnnotationIndex,
-        _ty: &mut CanonicalUserTypeAnnotation,
-    ) {
-        // User type annotations represent the types that the user
-        // wrote in the progarm. We don't want to erase the regions
-        // from these types: rather, we want to add them as
-        // constraints at type-check time.
-        debug!("visit_user_type_annotation: skipping renumber");
-    }
-
     fn visit_substs(&mut self, substs: &mut &'tcx Substs<'tcx>, location: Location) {
         debug!("visit_substs(substs={:?}, location={:?})", substs, location);
 

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -748,7 +748,7 @@ struct TypeChecker<'a, 'gcx: 'tcx, 'tcx: 'a> {
     /// annotations. Part of the reason for this setup is that it allows us to enforce basic
     /// WF criteria on the types even if the code that referenced them is dead
     /// code (see #54943).
-    instantiated_type_annotations: FxHashMap<UserTypeAnnotationIndex, UserType<'tcx>>,
+    instantiated_type_annotations: FxHashMap<UserTypeAnnotationIndex, Ty<'tcx>>,
 }
 
 struct BorrowCheckContext<'a, 'tcx: 'a> {
@@ -920,17 +920,58 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
              self.mir.user_type_annotations
         );
         for annotation_index in self.mir.user_type_annotations.indices() {
-            let CanonicalUserTypeAnnotation { span, ref user_ty } =
+            let CanonicalUserTypeAnnotation { span, ref user_ty, inferred_ty } =
                 self.mir.user_type_annotations[annotation_index];
-            let (mut annotation, _) = self.infcx.instantiate_canonical_with_fresh_inference_vars(
+            let (annotation, _) = self.infcx.instantiate_canonical_with_fresh_inference_vars(
                 span, user_ty
             );
             match annotation {
-                UserType::Ty(ref mut ty) =>
-                    *ty = self.normalize(ty, Locations::All(span)),
-                _ => {},
+                UserType::Ty(mut ty) => {
+                    ty = self.normalize(ty, Locations::All(span));
+
+                    if let Err(terr) = self.eq_types(
+                        ty,
+                        inferred_ty,
+                        Locations::All(span),
+                        ConstraintCategory::BoringNoLocation,
+                    ) {
+                        span_mirbug!(
+                            self,
+                            self.mir.user_type_annotations[annotation_index],
+                            "bad user type ({:?} = {:?}): {:?}",
+                            ty,
+                            inferred_ty,
+                            terr
+                        );
+                    }
+
+                    self.prove_predicate(
+                        ty::Predicate::WellFormed(inferred_ty),
+                        Locations::All(span),
+                        ConstraintCategory::TypeAnnotation,
+                    );
+                },
+                UserType::TypeOf(def_id, user_substs) => {
+                    if let Err(terr) = self.fully_perform_op(
+                        Locations::All(span),
+                        ConstraintCategory::BoringNoLocation,
+                        self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
+                            inferred_ty, def_id, user_substs,
+                        )),
+                    ) {
+                        span_mirbug!(
+                            self,
+                            self.mir.user_type_annotations[annotation_index],
+                            "bad user type AscribeUserType({:?}, {:?} {:?}): {:?}",
+                            inferred_ty,
+                            def_id,
+                            user_substs,
+                            terr
+                        );
+                    }
+                },
             }
-            self.instantiated_type_annotations.insert(annotation_index, annotation);
+            self.instantiated_type_annotations.insert(annotation_index, inferred_ty);
         }
         debug!(
             "instantiate_user_type_annotations: instantiated_type_annotations={:?}",
@@ -1067,58 +1108,23 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
             a, v, user_ty, locations,
         );
 
-        let type_annotation = self.instantiated_type_annotations[&user_ty.base];
-        match type_annotation {
-            UserType::Ty(ty) => {
-                // The `TypeRelating` code assumes that "unresolved inference
-                // variables" appear in the "a" side, so flip `Contravariant`
-                // ambient variance to get the right relationship.
-                let v1 = ty::Contravariant.xform(v);
-                let tcx = self.infcx.tcx;
+        let annotated_type = self.instantiated_type_annotations[&user_ty.base];
+        let mut curr_projected_ty = PlaceTy::from_ty(annotated_type);
 
-                // We need to follow any provided projetions into the type.
-                //
-                // if we hit a ty var as we descend, then just skip the
-                // attempt to relate the mir local with any type.
-                #[derive(Debug)] struct HitTyVar;
-                let mut curr_projected_ty: Result<PlaceTy, HitTyVar>;
-
-                curr_projected_ty = Ok(PlaceTy::from_ty(ty));
-                for proj in &user_ty.projs {
-                    let projected_ty = if let Ok(projected_ty) = curr_projected_ty {
-                        projected_ty
-                    } else {
-                        break;
-                    };
-                    curr_projected_ty = projected_ty.projection_ty_core(
-                        tcx, proj, |this, field, &()| {
-                            if this.to_ty(tcx).is_ty_var() {
-                                Err(HitTyVar)
-                            } else {
-                                let ty = this.field_ty(tcx, field);
-                                Ok(self.normalize(ty, locations))
-                            }
-                        });
-                }
-                debug!("user_ty base: {:?} freshened: {:?} projs: {:?} yields: {:?}",
-                       user_ty.base, ty, user_ty.projs, curr_projected_ty);
+        let tcx = self.infcx.tcx;
 
-                if let Ok(projected_ty) = curr_projected_ty {
-                    let ty = projected_ty.to_ty(tcx);
-                    self.relate_types(ty, v1, a, locations, category)?;
-                }
-            }
-            UserType::TypeOf(def_id, user_substs) => {
-                let projs = self.infcx.tcx.intern_projs(&user_ty.projs);
-                self.fully_perform_op(
-                    locations,
-                    category,
-                    self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
-                        a, v, def_id, user_substs, projs,
-                    )),
-                )?;
-            }
+        for proj in &user_ty.projs {
+            let projected_ty = curr_projected_ty.projection_ty_core(tcx, proj, |this, field, &()| {
+                let ty = this.field_ty(tcx, field);
+                self.normalize(ty, locations)
+            });
+            curr_projected_ty = projected_ty;
         }
+        debug!("user_ty base: {:?} freshened: {:?} projs: {:?} yields: {:?}",
+                user_ty.base, annotated_type, user_ty.projs, curr_projected_ty);
+
+        let ty = curr_projected_ty.to_ty(tcx);
+        self.relate_types(a, v, ty, locations, category)?;
 
         Ok(())
     }

src/librustc_mir/build/expr/as_constant.rs

@@ -31,10 +31,11 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 value,
             } => this.as_constant(value),
             ExprKind::Literal { literal, user_ty } => {
-                let user_ty = user_ty.map(|ty| {
+                let user_ty = user_ty.map(|user_ty| {
                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
                         span,
-                        user_ty: ty,
+                        user_ty,
+                        inferred_ty: ty,
                     })
                 });
                 Constant {

src/librustc_mir/build/expr/as_place.rs

@@ -134,7 +134,11 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 let place = unpack!(block = this.as_place(block, source));
                 if let Some(user_ty) = user_ty {
                     let annotation_index = this.canonical_user_type_annotations.push(
-                        CanonicalUserTypeAnnotation { span: source_info.span, user_ty }
+                        CanonicalUserTypeAnnotation {
+                            span: source_info.span,
+                            user_ty,
+                            inferred_ty: expr.ty,
+                        }
                     );
                     this.cfg.push(
                         block,
@@ -157,7 +161,11 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 );
                 if let Some(user_ty) = user_ty {
                     let annotation_index = this.canonical_user_type_annotations.push(
-                        CanonicalUserTypeAnnotation { span: source_info.span, user_ty }
+                        CanonicalUserTypeAnnotation {
+                            span: source_info.span,
+                            user_ty,
+                            inferred_ty: expr.ty,
+                        }
                     );
                     this.cfg.push(
                         block,

src/librustc_mir/build/expr/as_rvalue.rs

@@ -331,10 +331,12 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                         .collect()
                 };
 
+                let inferred_ty = expr.ty;
                 let user_ty = user_ty.map(|ty| {
                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
                         span: source_info.span,
                         user_ty: ty,
+                        inferred_ty,
                     })
                 });
                 let adt = box AggregateKind::Adt(