Unexpected parsing error in shorthand lambda

[DedSec256]

let _ = 1 |> _.ToString()
1 |> _.ToString()

.NET 8.0.100-rc.2.23502.2

[abonie]

Can you share sdk version?

[DedSec256]

@abonie, reproducible in .NET 8.0.100-rc.2.23502.2
Also it can be reproduced via test in the latest main branch

[<Fact>]
let Test () =
    Fsx """
let _ = 1 |> _.ToString()
1 |> _.ToString()"""
    |> withLangVersion80
    |> typecheck
    |> shouldSucceed

[abonie]

Hmm... curious thing is that it does not repro for me in fsi or when I create a project with dotnet new console ... but it does repro when I create a new console app project with VS or with the unit test method @DedSec256 proposed.

[vzarytovskii]

Might be because it's on a top level, due to how we codegen/lift stuff? Is there a difference top level vs inside function/method?

[auduchinok]

Might be because it's on a top level, due to how we codegen/lift stuff? Is there a difference top level vs inside function/method?

Yes, there're some parsing differences IIRC, i.e. not every expression normally can be parsed at top level. However, here the lambda is inside a binary application expression, so I'd probably expect it to work (though, it depends on the implementation).

[abonie]

Yeah, if the code snippet is not top level it does not repro anymore

[T-Gro]

Yep, this is it.
This error message is done based on the shape of the parsed SyntaxTree - this is the error I added to make things like _."a" invalid, but the top-level statement situation needs special casing here.