[ConstraintLocator] Add a new element - pattern binding element

The new element points to an index of a particular pattern in a
pattern binding declaration.

Author: xedin

include/swift/Sema/ConstraintLocator.h

@@ -1058,6 +1058,19 @@ class LocatorPathElt::ClosureBodyElement final
   }
 };
 
+class LocatorPathElt::PatternBindingElement final
+    : public StoredIntegerElement<1> {
+public:
+  PatternBindingElement(unsigned index)
+      : StoredIntegerElement(ConstraintLocator::PatternBindingElement, index) {}
+
+  unsigned getIndex() const { return getValue(); }
+
+  static bool classof(const LocatorPathElt *elt) {
+    return elt->getKind() == ConstraintLocator::PatternBindingElement;
+  }
+};
+
 namespace details {
   template <typename CustomPathElement>
   class PathElement {

include/swift/Sema/ConstraintLocatorPathElts.def

@@ -232,6 +232,9 @@ SIMPLE_LOCATOR_PATH_ELT(ImplicitDynamicMemberSubscript)
 /// The element of the closure body e.g. statement, declaration, or expression.
 CUSTOM_LOCATOR_PATH_ELT(ClosureBodyElement)
 
+/// The element of the pattern binding declaration.
+CUSTOM_LOCATOR_PATH_ELT(PatternBindingElement)
+
 #undef LOCATOR_PATH_ELT
 #undef CUSTOM_LOCATOR_PATH_ELT
 #undef SIMPLE_LOCATOR_PATH_ELT

lib/Sema/ConstraintLocator.cpp

@@ -96,6 +96,7 @@ unsigned LocatorPathElt::getNewSummaryFlags() const {
   case ConstraintLocator::ClosureBodyElement:
   case ConstraintLocator::PackType:
   case ConstraintLocator::PackElement:
+  case ConstraintLocator::PatternBindingElement:
     return 0;
 
   case ConstraintLocator::FunctionArgument:
@@ -578,6 +579,14 @@ void ConstraintLocator::dump(SourceManager *sm, raw_ostream &out) const {
       out << "pack element #" << llvm::utostr(packElt.getIndex());
       break;
     }
+
+    case PatternBindingElement: {
+      auto patternBindingElt =
+          elt.castTo<LocatorPathElt::PatternBindingElement>();
+      out << "pattern binding element #"
+          << llvm::utostr(patternBindingElt.getIndex());
+      break;
+    }
     }
   }
   out << ']';