NullableAttributes.cs

// This file has been borrowed from <https://github.com/dotnet/runtime> with the following license notice:
// 
//      Licensed to the .NET Foundation under one or more agreements.
//      The .NET Foundation licenses this file to you under the MIT license.
// 
// Only trivial changes have been made to this source file, such as formatting and modern C# features.

namespace System.Diagnostics.CodeAnalysis
{
#if !NETSTANDARD2_1
    /// <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 SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#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 SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#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 SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#endif
        sealed class MaybeNullAttribute : Attribute { }

    /// <summary>Specifies that an output will not be null even if the corresponding type allows it. Specifies that an input argument was not null when the call returns.</summary>
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
#if SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#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>
    /// <remarks>Initializes the attribute with the specified return value condition.</remarks>
    /// <param name="returnValue">
    /// The return value condition. If the method returns this value, the associated parameter may be null.
    /// </param>
    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
#if SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#endif
        sealed class MaybeNullWhenAttribute(bool returnValue) : Attribute
    {

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

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

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

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

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

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

    /// <summary>Specifies that the method will not return if the associated Boolean parameter is passed the specified value.</summary>
    /// <remarks>Initializes the attribute with the specified parameter value.</remarks>
    /// <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>
    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
#if SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#endif
        sealed class DoesNotReturnIfAttribute(bool parameterValue) : Attribute
    {

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

    /// <summary>Specifies that the method or property will ensure that the listed field and property members have not-null values.</summary>
    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
#if SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#endif
        sealed class MemberNotNullAttribute : Attribute
    {
        /// <summary>Initializes the attribute with a field or property member.</summary>
        /// <param name="member">
        /// The field or property member that is promised to be not-null.
        /// </param>
        public MemberNotNullAttribute(string member) => Members = [member];

        /// <summary>Initializes the attribute with the list of field and property members.</summary>
        /// <param name="members">
        /// The list of field and property members that are promised to be not-null.
        /// </param>
        public MemberNotNullAttribute(params string[] members) => Members = members;

        /// <summary>Gets field or property member names.</summary>
        public string[] Members { get; }
    }

    /// <summary>Specifies that the method or property will ensure that the listed field and property members have not-null values when returning with the specified return value condition.</summary>
    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
#if SYSTEM_PRIVATE_CORELIB
    public
#else
    internal
#endif
        sealed class MemberNotNullWhenAttribute : Attribute
    {
        /// <summary>Initializes the attribute with the specified return value condition and a field or property member.</summary>
        /// <param name="returnValue">
        /// The return value condition. If the method returns this value, the associated parameter will not be null.
        /// </param>
        /// <param name="member">
        /// The field or property member that is promised to be not-null.
        /// </param>
        public MemberNotNullWhenAttribute(bool returnValue, string member)
        {
            ReturnValue = returnValue;
            Members = [member];
        }

        /// <summary>Initializes the attribute with the specified return value condition and list of field and property members.</summary>
        /// <param name="returnValue">
        /// The return value condition. If the method returns this value, the associated parameter will not be null.
        /// </param>
        /// <param name="members">
        /// The list of field and property members that are promised to be not-null.
        /// </param>
        public MemberNotNullWhenAttribute(bool returnValue, params string[] members)
        {
            ReturnValue = returnValue;
            Members = members;
        }

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

        /// <summary>Gets field or property member names.</summary>
        public string[] Members { get; }
    }
}