[CSSimplify] Delay matching tuple types with at least 2 elements until

all pack type variables are resolved.

Author: hborla

lib/Sema/CSSimplify.cpp

@@ -6575,6 +6575,26 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
     }
 
     case TypeKind::Tuple: {
+       auto type1 = simplifyType(desugar1)->getDesugaredType();
+       auto type2 = simplifyType(desugar2)->getDesugaredType();
+
+      // FIXME: TuplePackMatcher doesn't correctly handle matching two
+       // abstract contextual tuple types in a generic context.
+       if (type1->isEqual(type2))
+         return getTypeMatchSuccess();
+
+      // If the tuple has more than one element, packs must be
+      // resolved before matching.
+      SmallPtrSet<TypeVariableType *, 2> typeVars;
+      type1->getTypeVariables(typeVars);
+      type2->getTypeVariables(typeVars);
+      if (desugar1->getAs<TupleType>()->getNumElements() > 1 &&
+          llvm::any_of(typeVars, [](auto *tv) {
+            return tv->getImpl().canBindToPack();
+          })) {
+        return formUnsolvedResult();
+      }
+
       // Add each tuple type to the locator before matching the element types.
       // This is useful for diagnostics, because the error message can use the
       // full tuple type for several element mismatches. Use the original types