erase types in the move-path abstract domain

Leaving types unerased would lead to 2 types with a different "name"
getting different move-paths, which would cause major brokenness (see
e.g. #42903).

This does not fix any *known* issue, but is required if we want to use
abs_domain with non-erased regions (because the same can easily
have different names). cc @RalfJung.

src/librustc/ich/impls_mir.rs

@@ -258,10 +258,11 @@ fn hash_stable<W: StableHasherResult>(&self,
     }
 }
 
-impl<'a, 'gcx, 'tcx, B, V> HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
-for mir::Projection<'tcx, B, V>
+impl<'a, 'gcx, 'tcx, B, V, T> HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
+for mir::Projection<'tcx, B, V, T>
     where B: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>,
-          V: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
+          V: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>,
+          T: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
 {
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'a, 'gcx, 'tcx>,
@@ -276,9 +277,10 @@ fn hash_stable<W: StableHasherResult>(&self,
     }
 }
 
-impl<'a, 'gcx, 'tcx, V> HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
-for mir::ProjectionElem<'tcx, V>
-    where V: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
+impl<'a, 'gcx, 'tcx, V, T> HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
+for mir::ProjectionElem<'tcx, V, T>
+    where V: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>,
+          T: HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
 {
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'a, 'gcx, 'tcx>,
@@ -286,7 +288,7 @@ fn hash_stable<W: StableHasherResult>(&self,
         mem::discriminant(self).hash_stable(hcx, hasher);
         match *self {
             mir::ProjectionElem::Deref => {}
-            mir::ProjectionElem::Field(field, ty) => {
+            mir::ProjectionElem::Field(field, ref ty) => {
                 field.hash_stable(hcx, hasher);
                 ty.hash_stable(hcx, hasher);
             }

src/librustc/mir/mod.rs

@@ -887,15 +887,15 @@ pub struct Static<'tcx> {
 /// shared between `Constant` and `Lvalue`. See the aliases
 /// `LvalueProjection` etc below.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
-pub struct Projection<'tcx, B, V> {
+pub struct Projection<'tcx, B, V, T> {
     pub base: B,
-    pub elem: ProjectionElem<'tcx, V>,
+    pub elem: ProjectionElem<'tcx, V, T>,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
-pub enum ProjectionElem<'tcx, V> {
+pub enum ProjectionElem<'tcx, V, T> {
     Deref,
-    Field(Field, Ty<'tcx>),
+    Field(Field, T),
     Index(V),
 
     /// These indices are generated by slice patterns. Easiest to explain
@@ -932,11 +932,11 @@ pub enum ProjectionElem<'tcx, V> {
 
 /// Alias for projections as they appear in lvalues, where the base is an lvalue
 /// and the index is an operand.
-pub type LvalueProjection<'tcx> = Projection<'tcx, Lvalue<'tcx>, Operand<'tcx>>;
+pub type LvalueProjection<'tcx> = Projection<'tcx, Lvalue<'tcx>, Operand<'tcx>, Ty<'tcx>>;
 
 /// Alias for projections as they appear in lvalues, where the base is an lvalue
 /// and the index is an operand.
-pub type LvalueElem<'tcx> = ProjectionElem<'tcx, Operand<'tcx>>;
+pub type LvalueElem<'tcx> = ProjectionElem<'tcx, Operand<'tcx>, Ty<'tcx>>;
 
 newtype_index!(Field, "field");
 
@@ -1720,8 +1720,8 @@ fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
     }
 }
 
-impl<'tcx, B, V> TypeFoldable<'tcx> for Projection<'tcx, B, V>
-    where B: TypeFoldable<'tcx>, V: TypeFoldable<'tcx>
+impl<'tcx, B, V, T> TypeFoldable<'tcx> for Projection<'tcx, B, V, T>
+    where B: TypeFoldable<'tcx>, V: TypeFoldable<'tcx>, T: TypeFoldable<'tcx>
 {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         use mir::ProjectionElem::*;
@@ -1729,7 +1729,7 @@ fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F)
         let base = self.base.fold_with(folder);
         let elem = match self.elem {
             Deref => Deref,
-            Field(f, ty) => Field(f, ty.fold_with(folder)),
+            Field(f, ref ty) => Field(f, ty.fold_with(folder)),
             Index(ref v) => Index(v.fold_with(folder)),
             ref elem => elem.clone()
         };
@@ -1745,7 +1745,7 @@ fn super_visit_with<Vs: TypeVisitor<'tcx>>(&self, visitor: &mut Vs) -> bool {
 
         self.base.visit_with(visitor) ||
             match self.elem {
-                Field(_, ty) => ty.visit_with(visitor),
+                Field(_, ref ty) => ty.visit_with(visitor),
                 Index(ref v) => v.visit_with(visitor),
                 _ => false
             }

src/librustc_mir/dataflow/move_paths/abs_domain.rs

@@ -23,11 +23,14 @@
 
 use rustc::mir::LvalueElem;
 use rustc::mir::{Operand, ProjectionElem};
+use rustc::ty::Ty;
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct AbstractOperand;
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+pub struct AbstractType;
 pub type AbstractElem<'tcx> =
-    ProjectionElem<'tcx, AbstractOperand>;
+    ProjectionElem<'tcx, AbstractOperand, AbstractType>;
 
 pub trait Lift {
     type Abstract;
@@ -37,6 +40,10 @@ impl<'tcx> Lift for Operand<'tcx> {
     type Abstract = AbstractOperand;
     fn lift(&self) -> Self::Abstract { AbstractOperand }
 }
+impl<'tcx> Lift for Ty<'tcx> {
+    type Abstract = AbstractType;
+    fn lift(&self) -> Self::Abstract { AbstractType }
+}
 impl<'tcx> Lift for LvalueElem<'tcx> {
     type Abstract = AbstractElem<'tcx>;
     fn lift(&self) -> Self::Abstract {
@@ -44,7 +51,7 @@ fn lift(&self) -> Self::Abstract {
             ProjectionElem::Deref =>
                 ProjectionElem::Deref,
             ProjectionElem::Field(ref f, ty) =>
-                ProjectionElem::Field(f.clone(), ty.clone()),
+                ProjectionElem::Field(f.clone(), ty.lift()),
             ProjectionElem::Index(ref i) =>
                 ProjectionElem::Index(i.lift()),
             ProjectionElem::Subslice {from, to} =>