Auto merge of #43128 - ibabushkin:master, r=eddyb

Implemented `TypeFoldable` for `TypeError`s.

This is quite handy in some user code, for instance to pull out type errors from an inference context when `fresh_substs_for_item` has been used before.

src/librustc/ty/structural_impls.rs

@@ -960,6 +960,20 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::error::ExpectedFoun
     }
 }
 
+impl<'tcx> TypeFoldable<'tcx> for type_variable::Default<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        type_variable::Default {
+            ty: self.ty.fold_with(folder),
+            origin_span: self.origin_span,
+            def_id: self.def_id
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.ty.visit_with(visitor)
+    }
+}
+
 impl<'tcx, T: TypeFoldable<'tcx>, I: Idx> TypeFoldable<'tcx> for IndexVec<I, T> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         self.iter().map(|x| x.fold_with(folder)).collect()
@@ -969,3 +983,79 @@ impl<'tcx, T: TypeFoldable<'tcx>, I: Idx> TypeFoldable<'tcx> for IndexVec<I, T>
         self.iter().any(|t| t.visit_with(visitor))
     }
 }
+
+impl<'tcx> TypeFoldable<'tcx> for ty::error::TypeError<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        use ty::error::TypeError::*;
+
+        match *self {
+            Mismatch => Mismatch,
+            UnsafetyMismatch(x) => UnsafetyMismatch(x.fold_with(folder)),
+            AbiMismatch(x) => AbiMismatch(x.fold_with(folder)),
+            Mutability => Mutability,
+            TupleSize(x) => TupleSize(x),
+            FixedArraySize(x) => FixedArraySize(x),
+            ArgCount => ArgCount,
+            RegionsDoesNotOutlive(a, b) => {
+                RegionsDoesNotOutlive(a.fold_with(folder), b.fold_with(folder))
+            },
+            RegionsNotSame(a, b) => {
+                RegionsNotSame(a.fold_with(folder), b.fold_with(folder))
+            },
+            RegionsNoOverlap(a, b) => {
+                RegionsNoOverlap(a.fold_with(folder), b.fold_with(folder))
+            },
+            RegionsInsufficientlyPolymorphic(a, b, ref c) => {
+                let c = c.clone();
+                RegionsInsufficientlyPolymorphic(a, b.fold_with(folder), c)
+            },
+            RegionsOverlyPolymorphic(a, b, ref c) => {
+                let c = c.clone();
+                RegionsOverlyPolymorphic(a, b.fold_with(folder), c)
+            },
+            IntMismatch(x) => IntMismatch(x),
+            FloatMismatch(x) => FloatMismatch(x),
+            Traits(x) => Traits(x),
+            VariadicMismatch(x) => VariadicMismatch(x),
+            CyclicTy => CyclicTy,
+            ProjectionNameMismatched(x) => ProjectionNameMismatched(x),
+            ProjectionBoundsLength(x) => ProjectionBoundsLength(x),
+            Sorts(x) => Sorts(x.fold_with(folder)),
+            TyParamDefaultMismatch(ref x) => TyParamDefaultMismatch(x.fold_with(folder)),
+            ExistentialMismatch(x) => ExistentialMismatch(x.fold_with(folder)),
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        use ty::error::TypeError::*;
+
+        match *self {
+            UnsafetyMismatch(x) => x.visit_with(visitor),
+            AbiMismatch(x) => x.visit_with(visitor),
+            RegionsDoesNotOutlive(a, b) |
+            RegionsNotSame(a, b) |
+            RegionsNoOverlap(a, b) => {
+                a.visit_with(visitor) || b.visit_with(visitor)
+            },
+            RegionsInsufficientlyPolymorphic(_, b, _) |
+            RegionsOverlyPolymorphic(_, b, _) => {
+                b.visit_with(visitor)
+            },
+            Sorts(x) => x.visit_with(visitor),
+            TyParamDefaultMismatch(ref x) => x.visit_with(visitor),
+            ExistentialMismatch(x) => x.visit_with(visitor),
+            Mismatch |
+            Mutability |
+            TupleSize(_) |
+            FixedArraySize(_) |
+            ArgCount |
+            IntMismatch(_) |
+            FloatMismatch(_) |
+            Traits(_) |
+            VariadicMismatch(_) |
+            CyclicTy |
+            ProjectionNameMismatched(_) |
+            ProjectionBoundsLength(_) => false,
+        }
+    }
+}