Required polyfill.cs

#if !NET7_0_OR_GREATER
namespace System.Runtime.CompilerServices;
#endif

#if !NET5_0_OR_GREATER
internal static class IsExternalInit { }
#endif

#if !NET7_0_OR_GREATER
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Struct, Inherited = false)]
internal sealed class RequiredMemberAttribute : Attribute { }

[AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
internal sealed class CompilerFeatureRequiredAttribute : Attribute
{
    public CompilerFeatureRequiredAttribute(string featureName) => FeatureName = featureName;

    public string FeatureName { get; }
    public bool IsOptional { get; init; }

    public const string RefStructs = nameof(RefStructs);
    public const string RequiredMembers = nameof(RequiredMembers);
}
#endif