add a Copyable conformance for PackExpansionType

lib/AST/Module.cpp

@@ -1724,6 +1724,16 @@ LookupConformanceInModuleRequest::evaluate(
     return getBuiltinBuiltinTypeConformance(type, builtinType, protocol);
   }
 
+  // Specific handling of Copyable for pack expansions.
+  if (auto packExpansion = type->getAs<PackExpansionType>()) {
+    if (protocol->isSpecificProtocol(KnownProtocolKind::Copyable)) {
+      auto patternType = packExpansion->getPatternType();
+      return (patternType->isTypeParameter()
+               ? ProtocolConformanceRef(protocol)
+               : mod->lookupConformance(patternType, protocol));
+    }
+  }
+
   auto nominal = type->getAnyNominal();
 
   // If we don't have a nominal type, there are no conformances.