[API Proposal]: Add System.Runtime.CompilerServices.RefSafetyRulesAttribute

[cston]

Background and motivation

The C# compiler emits a [module: RefSafetyRules(11)] attribute to modules compiled with -langversion:11 or above, or compiled with .NET 7 or above, to indicate that the module was compiled with C#11 ref safety rules.

The RefSafetyRulesAttribute type definition should be added to the BCL to avoid having the compiler emit the attribute definition to each module.

See RefSafetyRulesAttribute.

API Proposal

namespace System.Runtime.CompilerServices
{
    [AttributeUsage(AttributeTargets.Module, AllowMultiple = false, Inherited = false)]
    public sealed class RefSafetyRulesAttribute : Attribute
    {
        public RefSafetyRulesAttribute(int version) { Version = version; }
        public int Version;
    }
}

API Usage

The RefSafetyRulesAttribute type is for compiler use only - it is not permitted in source.

Alternative Designs

No response

Risks

No response

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Issue Details

---

Background and motivation

The C# compiler emits a [module: RefSafetyRules(11)] attribute to modules compiled with -langversion:11 or above, or compiled with .NET 7 or above, to indicate that the module was compiled with C#11 ref safety rules.

The RefSafetyRulesAttribute type definition should be added to the BCL to avoid having the compiler emit the attribute definition to each module.

See RefSafetyRulesAttribute.

API Proposal

namespace System.Runtime.CompilerServices
{
    [AttributeUsage(AttributeTargets.Module, AllowMultiple = false, Inherited = false)]
    public sealed class RefSafetyRulesAttribute : Attribute
    {
        public RefSafetyRulesAttribute(int version) { Version = version; }
        public int Version;
    }
}

API Usage

The RefSafetyRulesAttribute type is for compiler use only - it is not permitted in source.

Alternative Designs

No response

Risks

No response

Author:	cston
Assignees:	-
Labels:	api-suggestion, area-System.Runtime.CompilerServices
Milestone:	-

[cston]

cc @jaredpar, @AaronRobinsonMSFT

[AaronRobinsonMSFT]

@cston This looks like a .NET 7 need, correct?

[cston]

@AaronRobinsonMSFT, this can wait until .NET 8.

[stephentoub]

There are other attributes the compiler will emit as internal into an assembly and that we haven't exposed from corelib, e.g. NullableAttribute, NullableContextAttribute, EmbeddedAttribute, maybe others? They are similarly not meant to be uttered in source. Are we interested in bringing them all into corelib as public? I'm wondering if/how RefSafetyRules is special.

[jaredpar]

I'm wondering if/how RefSafetyRules is special

The other ones require some level of opt in. For instance you aren't going to see any of the Nullable* ones unless you opt into nullability in some way. It's pay for play in that way.

The ref safety rules one though we include on almost all assemblies. There isn't as much of a trigger to opt into ref rules. Originally we conditioned the rule on a signature having a out, ref or ref struct parameter or return. That didn't sit 100% right with us. There was worry about missing checks, future proofing, etc ... and eventually felt it was better to just emit always. At that point it felt like it was better to have in corelib.

Also if there was a better trigger for when to emit this, be willing to listen to that option 😄

[vitek-karas]

Is the RefSafetyRulesAttribute used for anything at runtime? If not we should probably add it to the list of attributes aggressive trimming removes by default - otherwise this adds two types into every assembly (RefSafetyRulesAttribute and EmbeddedAttribute), yes they are small... but still.

/cc @marek-safar