[ConstraintLocator] Add a new locator accessor to check whether it belongs to key path component result

Author: xedin

include/swift/Sema/ConstraintLocator.h

@@ -204,6 +204,10 @@ class ConstraintLocator : public llvm::FoldingSetNode {
   /// components.
   bool isForKeyPathComponent() const;
 
+  /// Determine whether this locator points to a result type of
+  /// a key path component.
+  bool isForKeyPathComponentResult() const;
+
   /// Determine whether this locator points to the generic parameter.
   bool isForGenericParameter() const;
 

lib/Sema/ConstraintLocator.cpp

@@ -177,6 +177,10 @@ bool ConstraintLocator::isForKeyPathComponent() const {
   });
 }
 
+bool ConstraintLocator::isForKeyPathComponentResult() const {
+  return isLastElement<LocatorPathElt::KeyPathComponentResult>();
+}
+
 bool ConstraintLocator::isForGenericParameter() const {
   return isLastElement<LocatorPathElt::GenericParameter>();
 }