[IUO] Add a locator for the result of a cast to an IUO type.

Not used yet, so NFC.

lib/Sema/ConstraintLocator.cpp

@@ -78,6 +78,7 @@ void ConstraintLocator::Profile(llvm::FoldingSetNodeID &id, Expr *anchor,
     case KeyPathComponent:
     case ConditionalRequirement:
     case TypeParameterRequirement:
+    case ImplicitlyUnwrappedCoercionResult:
       if (unsigned numValues = numNumericValuesInPathElement(elt.getKind())) {
         id.AddInteger(elt.getValue());
         if (numValues > 1)
@@ -248,6 +249,10 @@ void ConstraintLocator::dump(SourceManager *sm, raw_ostream &out) {
     case TypeParameterRequirement:
       out << "type parameter requirement #" << llvm::utostr(elt.getValue());
       break;
+
+    case ImplicitlyUnwrappedCoercionResult:
+      out << "implictly unwrapped coercion result";
+      break;
     }
   }
 

lib/Sema/ConstraintLocator.h

@@ -127,6 +127,9 @@ public:
     ConditionalRequirement,
     /// A single requirement placed on the type parameters.
     TypeParameterRequirement,
+    /// \brief A coercion to an Optional type that can potentially be
+    /// force-unwrapped to the underlying type.
+    ImplicitlyUnwrappedCoercionResult,
   };
 
   /// \brief Determine the number of numeric values used for the given path
@@ -159,6 +162,7 @@ public:
     case Requirement:
     case Witness:
     case OpenedGeneric:
+    case ImplicitlyUnwrappedCoercionResult:
       return 0;
 
     case GenericArgument:
@@ -221,6 +225,7 @@ public:
     case KeyPathComponent:
     case ConditionalRequirement:
     case TypeParameterRequirement:
+    case ImplicitlyUnwrappedCoercionResult:
       return 0;
 
     case FunctionArgument: