[ConstraintSystem] Add a locator element to represent a fallback type

Author: xedin

include/swift/Sema/ConstraintLocatorPathElts.def

@@ -281,6 +281,9 @@ SIMPLE_LOCATOR_PATH_ELT(ThrownErrorType)
 /// A type coercion operand.
 SIMPLE_LOCATOR_PATH_ELT(CoercionOperand)
 
+/// A fallback type for some AST location (i.e. key path literal).
+SIMPLE_LOCATOR_PATH_ELT(FallbackType)
+
 #undef LOCATOR_PATH_ELT
 #undef CUSTOM_LOCATOR_PATH_ELT
 #undef SIMPLE_LOCATOR_PATH_ELT

lib/Sema/ConstraintLocator.cpp

@@ -110,6 +110,7 @@ unsigned LocatorPathElt::getNewSummaryFlags() const {
   case ConstraintLocator::CoercionOperand:
   case ConstraintLocator::PackExpansionType:
   case ConstraintLocator::ThrownErrorType:
+  case ConstraintLocator::FallbackType:
     return 0;
 
   case ConstraintLocator::FunctionArgument:
@@ -524,6 +525,10 @@ void LocatorPathElt::dump(raw_ostream &out) const {
     out << "thrown error type";
     break;
   }
+  case ConstraintLocator::FallbackType: {
+    out << "fallback type";
+    break;
+  }
   }
 }
 

lib/Sema/ConstraintSystem.cpp

@@ -6044,6 +6044,7 @@ void constraints::simplifyLocator(ASTNode &anchor,
     case ConstraintLocator::WrappedValue:
     case ConstraintLocator::OptionalPayload:
     case ConstraintLocator::ImplicitlyUnwrappedDisjunctionChoice:
+    case ConstraintLocator::FallbackType:
       break;
     }