Removing empty lines in a class can remove all errors from that file

Version Used: 17.4.0 Preview 6.0 (and I’m pretty sure that this wasn’t an issue in Preview 2.1)

Steps to Reproduce:

I have a small example C# file in my normal project. This file has errors (unimplemented interface and missing async):

internal class Test : IEnumerable<int>
{
    public Task Method()
    {
        await Task.Delay(1000);
    }
}

I add a couple of empty lines in that file above the Method and then remove them randomly using Shift+Del.

Expected Behavior: Nothing weird should happen.

Actual Behavior: Each time I remove lines, one of three things that can happen in addition to the lines being gone:

1. Nothing else (most of the time)
2. Briefly, all red squiggles are gone and then come back (a couple of times)
3. All red squiggles vanish and don’t come back until the next edit (rarely)

The gif starts with 2. then shows a couple of 1. and ends with a 3.

[mavasani]

@Youssef1313 https://github.com/dotnet/roslyn/pull/64885 shouldn’t be causing this. I am seeing similar slowness in diagnostic computation in latest intpreview builds. Seems like an unrelated regression. I’ll investigate

[Tragetaschen]

I would say that the IDE feels a whole lot smoother in 17.5.0 Preview 4 and I haven’t seen anything like in the OP