Unexpected behavior with struct multicase unions

[cartermp]

The latest F# 4.1 compiler fails to compile either of the following code programs on .NET Core:

[<Struct>]
type Foo = Bar | Baz

[<EntryPoint>]
let main argv =
    printfn "Hello World from F#!"
    0 // return an integer exit code

[<Struct>]
type Foo = 
    | Bar of int
    | Baz of int

[<EntryPoint>]
let main argv =
    printfn "Hello World from F#!"
    0 // return an integer exit code

With this error:

FSC : error FS2014: A problem occurred writing the binary '/Users/phillip/scratch/test/obj/Debug/netcoreapp2.0/test.dll': Error in pass2 for type Program, error: Error in pass2 for type Foo, error: duplicate entry '.ctor' in method table [/Users/phillip/scratch/test/test.fsproj]

This is one rel/2.0.0 of the .NET CLI.

--- Old Issue ---

In VS "15" Preview 5, if you have the following:

[<Struct>]
type Shape =
    | Circle of radius: float
    | Square of side: double
    | Rectangle of sides: double*double

The following error occurs:

Error in pass2 for type Program, error: Error in pass2 for type Shape, error: duplicate entry '.ctor' in method table

If I remove the Square case , or change it to be of type int, it compiles.

[neildanson]

You also get the same in the case with something like this

[<Struct>]
type DU = A | B

I've not taken a look at the implementation of struct multi case unions, but I'm guessing that a unique constructor is built per signature of each case? That would explain why it fails for cases with duplicate signatures ?

[cloudRoutine]

I just ran into this issue too.

While it shows up in the build output, it does not in the error list

[amongonz]

I just installed F# support for the latest VS2017 RC and hit this issue. It fails every time two or more cases have the same type.

Inspecting the IL emitted for struct unions I see a private constructor for each case. I think the easiest fix would be having a single constructor, with a parameter for every field.

[dsyme]

@mistiara Yes, we need to document this limitation, it is a bug in F# 4.1. We will fix it.