Discriminated union .Is* properties causing compile time error

[p5ych08illy]

Compile time error since Visual Studio update: "Error in pass2 for type Foo, error: duplicate entry 'get_IsSZ' in method table."

Repro steps

Create blank F# class library

namespace FSharpClassLibrary4

module Say =
    let hello name =
        printfn "Hello %s" name

    type Foo = 
    | SZ
    | STZ
    | ZS
    | ASZ

Expected behavior

The example compiles successfully.

Actual behavior

Compile time error:
"A problem occurred writing the binary 'C:...\FSharpClassLibrary4\FSharpClassLibrary4\obj\Debug\net6.0\FSharpClassLibrary4.dll': Error in pass2 for type FSharpClassLibrary4.Say, error: Error in pass2 for type Foo, error: duplicate entry 'get_IsSZ' in method table"

Known workarounds

1. Use Language version 8
2. Rename SZ type not to begin with SZ

Related information

.NET SDK: 9.0.102
Visual Studio: 17.12.4

[T-Gro]

Hi @p5ych08illy ,

could you also share a project file for this repro?
I tried the posted sample (.NET 9 SDK) and did not get the mentioned error.

Is this a standalone repro, or is there additional code in the same file?

[p5ych08illy]

Hi @T-Gro ,

I attached the project. It contains only the code snippet I provided above.

FSharpClassLibrary4.zip

[T-Gro]

Do you by any chance have a Directory.props or Directory.targets in the folder hiearchy?

I tried a dotnet build of the project and it passes at me.
I also enforced the SDK via an added global.json file to be "version": "9.0.102" and it also passes.

Among others, your file specified a net9 target framework, but the error message below does have net6.0 in it - which gives me the idea of some parent folder affecting msbuild properties perharps?

[p5ych08illy]

I do not have any props or targets file.

I can successfully compile the project with dotnet build too.

If I try msbuild from a Developer Command prompt, I get the same error: "FSC : error FS2014: A problem occurred writing the binary 'obj\Debug\net9.0\refint\FSharpClassLibrary4.dll': Error in pass2 for type FSharpClassLibrary4.Say, error: Error in pass2 for type Foo, error: duplicate entry 'get_IsSZ' in method table [c:...\FSharpClassLibrary4\FSharpClassLibrary4\FSharpClassLibrary4.fsproj]"

I tried a lot of SDK and .NET version and I don't remember where I copied that error message (net6.0) from.

[vzarytovskii]

17.12 had an issue with ref assemblies and generating case testers. You can either update to latest (17.13 probably), or turn off reference assemblies <ProduceReferenceAssembly>false</ProduceReferenceAssembly>.

[p5ych08illy]

I can not test the Preview version (17.13) right now but the <ProduceReferenceAssembly>false</ProduceReferenceAssembly> did not help.

[vzarytovskii]

I can not test the Preview version (17.13) right now but the <ProduceReferenceAssembly>false</ProduceReferenceAssembly> did not help.

Hm, that is weird. This should've turned refassemblies emit off completely.