FS3511 warning when using `for...in` in task CE with .NET SDK 6.0.400 in Release builds

In the latest SDK (6.0.400), I’m receiving a FS3511 warning with for...in loops in task when building for Release. This warning wasn’t present in previous SDKs (e.g. 6.0.302)

Repro steps

1. In a new console application, replace Program.fs with the following code:

let v =
    task {
        for value in [1;2;3] do
            printfn $"{value}"
    }
    
printfn "Hello from F#"

1. dotnet build -c Release

Can repro with https://github.com/sasmithjr/FS3511-repro-for..in

Expected behavior

Builds without warning

Actual behavior

Receive the warning warning FS3511: This state machine is not statically compilable. A resumable code invocation at '(2,4--2,8)' could not be reduced. An alternative dynamic implementation will be used, which may be slower. Consider adjusting your code to ensure this state machine is statically compilable, or else suppress this warning.

Known workarounds

Suppressing the warning or using collection iter functions.

Related information

• Operating system: macOS 12.5 on an M1 MBP
• .NET Runtime kind (.NET Core, .NET Framework, Mono) .NET Core, SDK 6.0.400

Thanks for the help, and please let me know if I can provide anymore info.

[vzarytovskii]

Might be worth checking if this fixed in VS and VS4Mac 17.3 as I think there was a fix a similar code generation BUG see #13415 ?

No, I pretty sure it’s a different issue. But that fix might’ve caused it to break in .400.

[TimLariviere]

I encountered the exact same issue a few days ago, but it only shows up when I build in Release mode. Debug mode doesn’t seem to give me any warning.

Tried today building against dotnet 6.0.303 and 6.0.400. Both have the same behavior: no warning in debug build, warning FS3511 in release mode because of for .. in .. do inside a task.