NullableAttributes.cs

#pragma warning disable MA0048 // File name must match type name
#define INTERNAL_NULLABLE_ATTRIBUTES
#if NETSTANDARD2_0 ||  NETCOREAPP2_0 ||  NETCOREAPP2_1 ||  NETCOREAPP2_2 || NET45 || NET451 || NET452 || NET46 || NET461 || NET462 || NET47 || NET471 || NET472 || NET48

// https://github.com/dotnet/corefx/blob/48363ac826ccf66fbe31a5dcb1dc2aab9a7dd768/src/Common/src/CoreLib/System/Diagnostics/CodeAnalysis/NullableAttributes.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

namespace System.Diagnostics.CodeAnalysis
{
    /// <summary>Specifies that null is allowed as an input even if the corresponding type disallows it.</summary>
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class AllowNullAttribute : Attribute
    { }

    /// <summary>Specifies that null is disallowed as an input even if the corresponding type allows it.</summary>
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class DisallowNullAttribute : Attribute
    { }

    /// <summary>Specifies that an output may be null even if the corresponding type disallows it.</summary>
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class MaybeNullAttribute : Attribute
    { }

    /// <summary>Specifies that an output will not be null even if the corresponding type allows it.</summary>
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class NotNullAttribute : Attribute
    { }

    /// <summary>Specifies that when a method returns <see cref="ReturnValue"/>, the parameter may be null even if the corresponding type disallows it.</summary>
    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class MaybeNullWhenAttribute : Attribute
    {
        /// <summary>Initializes the attribute with the specified return value condition.</summary>
        /// <param name="returnValue">
        /// The return value condition. If the method returns this value, the associated parameter may be null.
        /// </param>
        public MaybeNullWhenAttribute(bool returnValue) => ReturnValue = returnValue;

        /// <summary>Gets the return value condition.</summary>
        public bool ReturnValue { get; }
    }

    /// <summary>Specifies that when a method returns <see cref="ReturnValue"/>, the parameter will not be null even if the corresponding type allows it.</summary>
    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class NotNullWhenAttribute : Attribute
    {
        /// <summary>Initializes the attribute with the specified return value condition.</summary>
        /// <param name="returnValue">
        /// The return value condition. If the method returns this value, the associated parameter will not be null.
        /// </param>
        public NotNullWhenAttribute(bool returnValue) => ReturnValue = returnValue;

        /// <summary>Gets the return value condition.</summary>
        public bool ReturnValue { get; }
    }

    /// <summary>Specifies that the output will be non-null if the named parameter is non-null.</summary>
    [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class NotNullIfNotNullAttribute : Attribute
    {
        /// <summary>Initializes the attribute with the associated parameter name.</summary>
        /// <param name="parameterName">
        /// The associated parameter name.  The output will be non-null if the argument to the parameter specified is non-null.
        /// </param>
        public NotNullIfNotNullAttribute(string parameterName) => ParameterName = parameterName;

        /// <summary>Gets the associated parameter name.</summary>
        public string ParameterName { get; }
    }

    /// <summary>Applied to a method that will never return under any circumstance.</summary>
    [AttributeUsage(AttributeTargets.Method, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class DoesNotReturnAttribute : Attribute
    { }

    /// <summary>Specifies that the method will not return if the associated Boolean parameter is passed the specified value.</summary>
    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
#if INTERNAL_NULLABLE_ATTRIBUTES
    internal
#else
    public
#endif
        sealed class DoesNotReturnIfAttribute : Attribute
    {
        /// <summary>Initializes the attribute with the specified parameter value.</summary>
        /// <param name="parameterValue">
        /// The condition parameter value. Code after the method will be considered unreachable by diagnostics if the argument to
        /// the associated parameter matches this value.
        /// </param>
        public DoesNotReturnIfAttribute(bool parameterValue) => ParameterValue = parameterValue;

        /// <summary>Gets the condition parameter value.</summary>
        public bool ParameterValue { get; }
    }
}
#endif

I think
#if NETSTANDARD2_0 || NETCOREAPP2_0 || NETCOREAPP2_1 || NETCOREAPP2_2 || NET45 || NET451 || NET452 || NET6 || NET461 || NET462 || NET47 || NET471 || NET472 || NET48
could be replaced with
#if !NETCOREAPP3_0 && !NETCOREAPP3_1

@vova-lantsov-dev Right now it will works with your simplified condition, but when a new platform will be released you'll have to update the condition. The current condition is longer but it should be stable.

Hi,
is it available as a nuget package or something ?

@MichalBrylka feel free to copy and paste it to your code. No need for external NuGet packages

@MichalBrylka feel free to copy and paste it to your code. No need for external NuGet packages

yes, I know. But recently new attributes were introduced i.e.
https://apisof.net/catalog/System.Diagnostics.CodeAnalysis.MemberNotNullAttribute

I know I can copy them manually as well, but it becomes tedious - especially since whole world needs to do that