C# 11 required properties do not compile on dotnet 6

[Varorbc]

[Update(jcouv):] The ask is that required properties not be recommended by the IDE on .NET 6 or lower.

Describe the bug

When I want to use required properties in a project targeting net6.0 with LangVersion set to latest I face some compile errors.

To Reproduce

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>net6.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <LangVersion>latest</LangVersion>
    </PropertyGroup>

</Project>

namespace Csharp11OnDotnet6;

public class Person
{
    public required string Name { get; init; }
}

2.dotnet build

Exceptions (if any)

error CS0656: Missing compiler required member 'System.Runtime.CompilerServices.RequiredMemberAttribute..ctor'
error CS0656: Missing compiler required member 'System.Runtime.CompilerServices.CompilerFeatureRequi
redAttribute..ctor'

Expected Behavior: build successful

[jcouv]

Those errors are expected. The "required members" feature is part of C# 11 and is only supported on .NET 7 and up.

[Varorbc]

@jcouv

1.use The "required members" feature is part of C# 11 and is only supported on .NET 7 and up instead of Missing compiler required member 'System.Runtime.CompilerServices.RequiredMemberAttribute..ctor' for the error

2.In .net 6 projects, IntelliSense should not recommend "required members"

[CyrusNajmabadi]

1.use The "required members" feature is part of C# 11 and is only supported on .NET 7 and up instead of

That's not the case here though. That's what we support (and so we don't do additional work in non-supported scenarios). If you added that attribute somehow, it would work (though we still dont' support that scenario), we don't block it. So the error you're getting is correct. The issue here is that those attributes are missing.

2.In .net 6 projects, IntelliSense should not recommend "required members"

Could you clarify what you mean? We def show things in the completion list to help speed up typing, regardless of version. We don't keep things out of the completion list as that can both be confusing, and it means if you try to type this, you can end up with some other piece of completed text.

[Varorbc]

So the error you're getting is correct. The issue here is that those attributes are missing.

Although I am aware of missing RequiredMemberAttribute, I am not aware that the root cause is that the "required members" feature is part of C# 11 and is only supported on .NET 7 and up, and if this can be explained, it would be better rather than asking questions

Could you clarify what you mean?

[Varorbc]

@CyrusNajmabadi @jcouv Please re-open

[jcouv]

Added a summary to OP: "The ask is that required properties not be recommended by the IDE on .NET 6 or lower." and assigned to the IDE team to take a look.

[CyrusNajmabadi]

The ide behavior is expected here. This is a viable way to fix the issue. And if we don't offer it, it could be confusing to the user (I believe we had this Convo when creating the feature). The user is not told to pick this option. They choose it, if appropriate, from the options offered. And if they want this, that means they're ok with moving forward.

[Varorbc]

when cleaning up code, should use Declare as nullable. not Make Property 'required'

[CyrusNajmabadi]

That is one of the options offered :-)

[Varorbc]

The cleanup worked fine when I hadn't updated vs to the latest version, but now that I've updated vs to the latest version, the project has a build error after the cleanup because required is used

[CyrusNajmabadi]

Can you give an example of what you mean? What was your code, and which fix did you pick?

[Varorbc]

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>net6.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <LangVersion>latest</LangVersion>
    </PropertyGroup>

</Project>

namespace Csharp11OnDotnet6;

public class Person
{
    public string Name { get; init; }
}

2.

3. run code clean(Profile 1)

[CyrusNajmabadi]

@mavasani Do you know how 'code cleanup' does this work?

[mavasani]

Also adding @sharwell

Choosing "Fix all warnings and errors set in EditorConfig" in the code cleanup profile leads to code cleanup sequentially attempting to fix all analyzer and compiler warnings and errors in code and considers all code fixer as potential candidates for providing a fix. It seems that we may need to add logic such that a code fixer can declaratively state that it shouldn't be included in code cleanup, and all fixers that fall in this bucket of "application introduces further compiler errors" should be marked for exclusion in code cleanup. @sharwell thoughts?

[CyrusNajmabadi]

Another option is to make this low-pri. Or order after "declare as nullable".

That said, neither of these is truly better than the other. So it's unclear to me what would be hte right behavior here as it depends on hte user.

[sharwell]

<TargetFramework>net6.0</TargetFramework>
<LangVersion>latest</LangVersion>

This is explicitly instructing the compiler to ignore the official support matrix and force required members to be allowed for a mismatched target framework, and as such is not an officially supported scenario. As a result, the analyzers related to required members may report diagnostics, and those diagnostics would be fixed if the configuration instructs it to. The change expected here would be the analyzer(s) code fix which suggests the use of required members should only do so when the necessary attribute is present. It sounds like we already check language version, so only the attribute check would be new.