Attempting to create a new Quantum Register inside a custom gate definition crashes the server

[DRovara]

Description:

Trying to create a new register (qreg or creg) inside a custom gate definition causes the entire server to crash. It seems that the server's background process gets stuck in some very resource-intensive loop (eventually, it caused my entire system to crash), as the terminal displays no further logs and even trying to connect again through a new browser window or reloading the page doesn't work.

Expected Behavior:

While creating new registers inside a custom gate definition is not supported, it should not be enough to cause the server to crash. Instead, some error message should be displayed.

How to Reproduce:

The following minimal OpenQASM code example is enough to make the process crash:

qreg q[1];

gate test a {
  qreg crash[2];
  x a;
}

test q[0];

It will also crash if I create a creg instead.

[burgholzer]

Thanks for catching this! I fully agree that this should not be causing a server crash!
I would suspect that this is an issue with not catching an exception being thrown from the QASM parser in mqt-core.

I'll take a look!

[burgholzer]

This is being fixed in munich-quantum-toolkit/core#700

[burgholzer]

This is now live at https://www.cda.cit.tum.de/app/ddvis/ 🚀