CA1508 is triggered despite value being set

[ericstj]

Version Used:
.NET SDK:
Version: 10.0.100-rc.2.25462.101
Commit: 26861c107e
Workload version: 10.0.100-manifests.663d2eb1
MSBuild version: 17.15.0-preview-25462-101+26861c107

Steps to Reproduce:

1. Compile attached sample:

string? testValue = null;

var class2 = new Class2
{
    action = (value) => testValue = value
};

class2.Indirection();

if (testValue != null)
{
    // Do something
    Console.WriteLine(testValue);
}

public class Class2()
{
    public Action<string>? action { get; init; }
    public void Indirection()
    {
        if (action != null)
            action("Hello World!");
    }
}

repro_CA1508.zip

Diagnostic Id:
CA1508: Avoid dead conditional code

Expected Behavior:
Compile without warning

Actual Behavior:
Warning

warning CA1508: 'testValue != null' is always 'false'. Remove or refactor the condition(s) to avoid dead code. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1508)

This warning is clearly false, since running the application shows that testValue is not null. The analyzer is not able to see enough about the possibility of modification to testValue.

[bdukes]

Here's another variant that causes this warning incorrectly:

namespace CA1508Example;

public static class Class1
{
    public static async Task<int> GetValue(bool hasObject, bool reassign)
    {
        Func<object?> getObject = () => null;
        if (reassign)
        {
            getObject = () => hasObject ? null : new { };
        }

        var theObject = getObject();
        return theObject is null ? 0 : 1;
    }
}

This does not trigger the warning if the function is not async.