[TypeChecker] Add method to check whether a type variable represents a code completion token

Author: ahoppen

include/swift/Sema/ConstraintSystem.h

@@ -386,6 +386,10 @@ class TypeVariableType::Implementation {
 
   bool isTypeSequence() const;
 
+  /// Determine whether this type variable represents a code completion
+  /// expression.
+  bool isCodeCompletionToken() const;
+
   /// Retrieve the representative of the equivalence class to which this
   /// type variable belongs.
   ///

lib/Sema/TypeCheckConstraints.cpp

@@ -130,6 +130,10 @@ bool TypeVariableType::Implementation::isTypeSequence() const {
       && locator->getGenericParameter()->isTypeSequence();
 }
 
+bool TypeVariableType::Implementation::isCodeCompletionToken() const {
+  return locator && locator->directlyAt<CodeCompletionExpr>();
+}
+
 void *operator new(size_t bytes, ConstraintSystem& cs,
                    size_t alignment) {
   return cs.getAllocator().Allocate(bytes, alignment);