[AST] containsPackExpansion should not be used when type variables are involved

The constraint solver has its own version of this method which
know how to deal with pack expansion type variables.

Author: xedin

lib/AST/ParameterPack.cpp

@@ -117,8 +117,11 @@ unsigned TupleType::getNumScalarElements() const {
 }
 
 bool TupleType::containsPackExpansionType() const {
+  assert(!hasTypeVariable());
   for (auto elt : getElements()) {
-    if (elt.getType()->is<PackExpansionType>())
+    auto eltTy = elt.getType();
+    assert(!eltTy->hasTypeVariable());
+    if (eltTy->is<PackExpansionType>())
       return true;
   }
 
@@ -144,7 +147,9 @@ bool TupleType::isSingleUnlabeledPackExpansion() const {
 
 bool AnyFunctionType::containsPackExpansionType(ArrayRef<Param> params) {
   for (auto param : params) {
-    if (param.getPlainType()->is<PackExpansionType>())
+    auto paramTy = param.getPlainType();
+    assert(!paramTy->hasTypeVariable());
+    if (paramTy->is<PackExpansionType>())
       return true;
   }