SDK 7.0.200 creates false positive CS0165, Use of unassigned local variable

[pieter-venter]

Version Used:
SDK 7.0.200

Steps to Reproduce:

1. Create a new console application with this in Program.cs

class Program
{
    static async Task Main(string[] args)
    {
        DateTime timestamp;

        async Task DoSomething()
        {
            timestamp = DateTime.UtcNow;
            await Task.Delay(1);
        }

        await DoSomething();
        Console.WriteLine(timestamp);
    }
}

2. Run dotnet build
3. Observe the error:

MSBuild version 17.5.0-preview-23061-01+040e2a90e for .NET
  Determining projects to restore...
  All projects are up-to-date for restore.
/home/myuser/cs0165/Program.cs(14,27): error CS0165: Use of unassigned local variable 'timestamp' [/home/myuser/cs0165/cs0165.csproj]

Diagnostic Id:

cs0165

Compare to previous version
I compared using a docker image of the previous version of the SDK.

docker run -it mcr.microsoft.com/dotnet/sdk:7.0.103-jammy

Once inside, confirm version:

root@5328a15698be:/# dotnet --version
7.0.103

Then I created the same console app.

dotnet new console -n cs0165

and replace the contents of Program.cs with the code above.

dotnet build
MSBuild version 17.4.1+fedecea9d for .NET
  Determining projects to restore...
  All projects are up-to-date for restore.
  cs0165 -> /cs0165/bin/Debug/net7.0/cs0165.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:03.12

Also confirmed that it runs

root@5328a15698be:/cs0165# dotnet run
02/21/2023 21:52:21

[pieter-venter]

Leaving this here for posterity's sake:

• Duplicate of Definite assignment bug when not awaiting an async closure #43697
  Some more explanations here:
• Definite assignment bug when not awaiting an async closure #43697 (comment)
• Caller of an async local function cannot expect any of the callee’s code to execute #64482

The language rules are defined here. I think it could be clarified but I'm not a language/rules designer :)