Partial evaluation, and therefore QIR generation, is inherently susceptible to infinite loops and out-of-memory conditions since we're executing user code. So we can't prevent these fully.

However, the way these conditions are surfaced in the UI is not helpful. It looks like a bug in the extension, rather than a problem in the user code. I think we can do better by catching some of these fatal conditions and wrap them in a more helpful user message that tells them what to look for.

(If we wanted to get fancy, we can emit warnings from the evaluator itself if we detect that no progress is being made, but that would be pretty fancy. This issue is just about the UI.)

Current UI:

infinite loops (after a rather long timeout):

while 0 == 0 {}

infinite recursion in classical functions:

function Foo() : Unit {
    Foo();
}

infinite recursion in operations:

operation Foo() : Unit {
    Foo();
}