Fix CallOpSet copy/assignment to reset cq_tag

include/grpcpp/impl/codegen/call.h

@@ -624,6 +624,19 @@ class CallOpSet : public CallOpSetInterface,
                   public Op6 {
  public:
   CallOpSet() : cq_tag_(this), return_tag_(this), call_(nullptr) {}
+
+  // The copy constructor and assignment operator reset the value of
+  // cq_tag_ and return_tag_ since those are only meaningful on a specific
+  // object, not across objects.
+  CallOpSet(const CallOpSet& other)
+      : cq_tag_(this), return_tag_(this), call_(other.call_) {}
+  CallOpSet& operator=(const CallOpSet& other) {
+    cq_tag_ = this;
+    return_tag_ = this;
+    call_ = other.call_;
+    return *this;
+  }
+
   void FillOps(grpc_call* call, grpc_op* ops, size_t* nops) override {
     this->Op1::AddOp(ops, nops);
     this->Op2::AddOp(ops, nops);

src/cpp/server/server_cc.cc

@@ -685,8 +685,8 @@ void Server::PerformOpsOnCall(internal::CallOpSetInterface* ops,
   size_t nops = 0;
   grpc_op cops[MAX_OPS];
   ops->FillOps(call->call(), cops, &nops);
-  // TODO(vjpai): Use ops->cq_tag once this case supports callbacks
-  auto result = grpc_call_start_batch(call->call(), cops, nops, ops, nullptr);
+  auto result =
+      grpc_call_start_batch(call->call(), cops, nops, ops->cq_tag(), nullptr);
   if (result != GRPC_CALL_OK) {
     gpr_log(GPR_ERROR, "Fatal: grpc_call_start_batch returned %d", result);
     grpc_call_log_batch(__FILE__, __LINE__, GPR_LOG_SEVERITY_ERROR,