[ConstraintSystem] Add a locator path element for pack shapes, and use it for

type variables representing pack shapes.

Author: hborla

include/swift/Sema/ConstraintLocatorPathElts.def

@@ -195,6 +195,9 @@ CUSTOM_LOCATOR_PATH_ELT(PackType)
 /// An element of a pack type - the T in <T, U, V, ...>
 CUSTOM_LOCATOR_PATH_ELT(PackElement)
 
+/// The shape of a parameter pack.
+SIMPLE_LOCATOR_PATH_ELT(PackShape)
+
 /// An unresolved member.
 SIMPLE_LOCATOR_PATH_ELT(UnresolvedMember)
 

lib/Sema/CSSimplify.cpp

@@ -2498,10 +2498,9 @@ ConstraintSystem::matchPackExpansionTypes(PackExpansionType *expansion1,
                                           ConstraintKind kind, TypeMatchOptions flags,
                                           ConstraintLocatorBuilder locator) {
   // The count types of two pack expansion types must have the same shape.
-  //
-  // FIXME: Locator for diagnostics.
-  auto *loc = getConstraintLocator(locator);
-  auto *shapeTypeVar = createTypeVariable(loc, TVO_CanBindToPack);
+  auto *shapeLoc = getConstraintLocator(
+      locator.withPathElement(ConstraintLocator::PackShape));
+  auto *shapeTypeVar = createTypeVariable(shapeLoc, TVO_CanBindToPack);
   addConstraint(ConstraintKind::ShapeOf,
                 expansion1->getCountType(), shapeTypeVar, locator);
   addConstraint(ConstraintKind::ShapeOf,
@@ -14156,8 +14155,9 @@ void ConstraintSystem::addConstraint(Requirement req,
     auto type1 = req.getFirstType();
     auto type2 = req.getSecondType();
 
-    // FIXME: Locator for diagnostics
-    auto typeVar = createTypeVariable(getConstraintLocator(locator),
+    auto *shapeLoc = getConstraintLocator(
+        locator.withPathElement(ConstraintLocator::PackShape));
+    auto typeVar = createTypeVariable(shapeLoc,
                                       TVO_CanBindToPack);
 
     addConstraint(ConstraintKind::ShapeOf, type1, typeVar, locator);

lib/Sema/ConstraintLocator.cpp

@@ -97,6 +97,7 @@ unsigned LocatorPathElt::getNewSummaryFlags() const {
   case ConstraintLocator::SyntacticElement:
   case ConstraintLocator::PackType:
   case ConstraintLocator::PackElement:
+  case ConstraintLocator::PackShape:
   case ConstraintLocator::PatternBindingElement:
   case ConstraintLocator::NamedPatternDecl:
   case ConstraintLocator::AnyPatternDecl:
@@ -444,6 +445,11 @@ void LocatorPathElt::dump(raw_ostream &out) const {
     break;
   }
 
+  case ConstraintLocator::PackShape: {
+    out << "pack shape";
+    break;
+  }
+
   case ConstraintLocator::PatternBindingElement: {
     auto patternBindingElt =
         elt.castTo<LocatorPathElt::PatternBindingElement>();

lib/Sema/ConstraintSystem.cpp

@@ -5327,6 +5327,7 @@ void constraints::simplifyLocator(ASTNode &anchor,
       break;
 
     case ConstraintLocator::PackElement:
+    case ConstraintLocator::PackShape:
       break;
 
     case ConstraintLocator::PatternBindingElement: {