UseValueTasksCorrectlyAnalyzer throws ArgumentNullException

[DavidZidar]

Analyzer package

Microsoft.CodeAnalysis.FxCopAnalyzers

Package Version

v3.0.0 (Latest)

Diagnostic ID

CA2012 UseValueTasksCorrectlyAnalyzer

Repro steps

using System;
using System.Threading.Tasks;

class C
{
    public void GuardThenAssignVariable()
    {
        if (false) throw new Exception();
        var vt = Helpers.ReturnsValueTask();
    }
}

Expected behavior

UseValueTasksCorrectly should not throw.

Actual behavior

An async method with a guard clause that throws an exception in combination with storing ValueTask in a variable causes UseValueTasksCorrectlyAnalyzer to throw ArgumentNullException.

It seems that block.FallThroughSuccessor.Destination is null when handling the fall through successor since it is a throw expression which results in the call to seen.TryGetValue throw
ArgumentNullException because the key is a null value.

[stephentoub]

Thanks for reporting this.

[DavidZidar]

No problem!