// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
#if NETCOREAPP3_0_OR_GREATER
 
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
 
#pragma warning disable RS0016 // Add public types and members to the declared API (this is a supporting forwarder for an internal polyfill API)
[assembly: TypeForwardedTo(typeof(AllowNullAttribute))]
[assembly: TypeForwardedTo(typeof(DisallowNullAttribute))]
[assembly: TypeForwardedTo(typeof(MaybeNullAttribute))]
[assembly: TypeForwardedTo(typeof(NotNullAttribute))]
[assembly: TypeForwardedTo(typeof(MaybeNullWhenAttribute))]
[assembly: TypeForwardedTo(typeof(NotNullWhenAttribute))]
[assembly: TypeForwardedTo(typeof(NotNullIfNotNullAttribute))]
[assembly: TypeForwardedTo(typeof(DoesNotReturnAttribute))]
[assembly: TypeForwardedTo(typeof(DoesNotReturnIfAttribute))]
#pragma warning restore RS0016 // Add public types and members to the declared API
 
#endif
 
#if NET5_0_OR_GREATER
 
#pragma warning disable RS0016 // Add public types and members to the declared API (this is a supporting forwarder for an internal polyfill API)
[assembly: TypeForwardedTo(typeof(MemberNotNullAttribute))]
[assembly: TypeForwardedTo(typeof(MemberNotNullWhenAttribute))]
#pragma warning restore RS0016 // Add public types and members to the declared API
 
#endif
 
namespace System.Diagnostics.CodeAnalysis;
 
// Copied from https://github.com/dotnet/runtime
 
// Note: These attributes were introduced in .NET Core 3.0 and .NET 5.
 
#if !NETCOREAPP3_0_OR_GREATER

/// <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)]
internal 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)]
internal 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)]
internal 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)]
internal 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)]
internal 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)]
internal 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)]
internal 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)]
internal 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)]
internal 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
 
#if !NET5_0_OR_GREATER

/// <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)]
internal 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 = new[] { 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)]
internal 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 = new[] { 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; }
}
 
#endif