Warning FS3536: "(interface) is normally used as a type constraint in generic code" for extension method on interface in .NET 7 SDK #14480
Description
When compiling an extension method for an interface using .NET SDK 7 you now get a confusing FS3536 warning about type constraints. With .NET SDK 6 there was no such warning. I don't see anything wrong with the code, so as far as I can tell the warning is a bug.
Repro steps
Try to compile the following console EXE:
type INormalInterface =
abstract member IntMember: int
module INormalInterfaceExtensions =
type INormalInterface with
static member extMethod (a: INormalInterface) =
()
printfn "Hello from F#"
Project file:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net6.0</TargetFramework>
</PropertyGroup>
<ItemGroup>
<Compile Include="Program.fs" />
</ItemGroup>
</Project>
Expected behavior
Compiles with no warnings, same as with .NET 6 SDK.
Actual behavior
$ dotnet build
MSBuild version 17.4.0+18d5aef85 for .NET
Determining projects to restore...
Restored /home/em/src/FS3536/FS3536.fsproj (in 468 ms).
/home/em/src/FS3536/Program.fs(6,37): warning FS3536: 'INormalInterface' is normally used as a type constraint in generic code, e.g. "'T when ISomeInterface<'T>" or "let f (x: #ISomeInterface<_>)". See https://aka.ms/fsharp-iwsams for guidance. You can disable this warning by using '#nowarn "3536"' or '--nowarn:3536'. [/home/em/src/FS3536/FS3536.fsproj]
Known workarounds
Use .NET 6 SDK by creating a global.json file or suppress that specific warning like the message says.
- Operating system: Ubuntu 18.04
- .NET Runtime kind (.NET Core, .NET Framework, Mono): .NET 6.0.12
- .NET SDK: 7.0.101