AST: TupleType::get() asserts if pack expansion type is followed by an unlabeled element

Author: slavapestov

lib/AST/ASTContext.cpp

@@ -3135,6 +3135,15 @@ TupleType *TupleType::get(ArrayRef<TupleTypeElt> Fields, const ASTContext &C) {
     properties |= eltTy->getRecursiveProperties();
   }
 
+  // Enforce an invariant.
+  for (unsigned i = 0, e = Fields.size(); i < e; ++i) {
+    if (Fields[i].getType()->is<PackExpansionType>()) {
+      assert(i == e - 1 || Fields[i + 1].hasName() &&
+             "Tuple element with pack expansion type cannot be followed "
+             "by an unlabeled element");
+    }
+  }
+
   auto arena = getArena(properties);
 
   void *InsertPos = nullptr;

lib/AST/Type.cpp

@@ -5702,9 +5702,16 @@ case TypeKind::Id:
         anyChanged = true;
       }
 
+      // "Splat" the elements of the transformed pack expansion into the tuple.
       if (auto *transformedPack = transformedEltTy->getAs<PackType>()) {
-        elements.append(transformedPack->getElementTypes().begin(),
-                        transformedPack->getElementTypes().end());
+        auto transformedEltTypes = transformedPack->getElementTypes();
+        if (!transformedEltTypes.empty()) {
+          // Keep the label on the first element.
+
+          elements.push_back(elt.getWithType(transformedEltTypes.front()));
+          elements.append(transformedEltTypes.begin() + 1,
+                          transformedEltTypes.end());
+        }
       } else {
         // Add the new tuple element, with the transformed type.
         elements.push_back(elt.getWithType(transformedEltTy));