Using `TailCallAttribute` on a function that uses `use` does not result in expected warning

[ljb]

Recently I discovered that we got a stack overflow for a function that we had the TailCallAttribute on. It seems that the check doesn't work well for functions that uses use to dispose resources.

Repro steps

// Causes as warning which is expected. Causes a stack overflow
[<TailCall>]
let rec example1 () =
    let path = Path.GetTempFileName()
    use file = File.Open(path, FileMode.Open)

    example1 ()

// Does not cause a warning even tough it causes a stack overflow
[<TailCall>]
let rec example2 () =
    let path = Path.GetTempFileName()
    use file = File.Open(path, FileMode.Open)
    printfn "Hi!"

    example2 ()

Compile the code above. example1 results in warning as expected. example2 does not result in a warning.

A zip-file with this example is attached. Running dotnet build only gives a warning for the first function.
RecursionExample.zip

Expected behavior

Both functions should result in warnings regarding the TailCallAttribute.

Actual behavior

Only example1 results in a warning.

Known workarounds

In code reviews manually check that functions marked with TailCallAttribute doesn't use use.

Related information

• Windows 11
• .NET SDK 8.0.403
• FSharp.Core 8.0.401

[dawedawe]

Thanks for reporting. Will take a look soon.