AST: Add TypePosition::Shape

Author: slavapestov

include/swift/AST/Type.h

@@ -214,7 +214,7 @@ enum class ForeignRepresentableKind : uint8_t {
 /// therefore, the result type is in covariant position relative to the function
 /// type.
 struct TypePosition final {
-  enum : uint8_t { Covariant, Contravariant, Invariant };
+  enum : uint8_t { Covariant, Contravariant, Invariant, Shape };
 
 private:
   decltype(Covariant) kind;
@@ -224,6 +224,7 @@ struct TypePosition final {
 
   TypePosition flipped() const {
     switch (kind) {
+    case Shape:
     case Invariant:
       return *this;
     case Covariant:

lib/AST/Type.cpp

@@ -4677,7 +4677,7 @@ case TypeKind::Id:
       return Type();
 
     Type transformedCount =
-        expand->getCountType().transformWithPosition(pos, fn);
+        expand->getCountType().transformWithPosition(TypePosition::Shape, fn);
     if (!transformedCount)
       return Type();
 

lib/Sema/ConstraintSystem.cpp

@@ -2199,6 +2199,7 @@ static Type typeEraseExistentialSelfReferences(Type refTy, Type baseTy,
 
           case TypePosition::Contravariant:
           case TypePosition::Invariant:
+          case TypePosition::Shape:
             return Type(t);
           }