Backport nullable attributes

Author: commonsensesoftware

src/Common/src/Common.Backport/NullableAttributes.cs

@@ -0,0 +1,59 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+
+#pragma warning disable SA1402, SA1649
+
+// REF: https://github.com/dotnet/runtime/blob/1c8d37af80667daffb3cb80ce0fe915621e8f039/src/libraries/System.Private.CoreLib/src/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.
+namespace System.Diagnostics.CodeAnalysis;
+
+[AttributeUsage( AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false )]
+internal sealed class AllowNullAttribute : Attribute { }
+
+[AttributeUsage( AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false )]
+internal sealed class DisallowNullAttribute : Attribute { }
+
+[AttributeUsage( AttributeTargets.Method, Inherited = false )]
+internal sealed class DoesNotReturnAttribute : Attribute { }
+
+[AttributeUsage( AttributeTargets.Parameter )]
+internal sealed class DoesNotReturnIfAttribute : Attribute
+{
+    public DoesNotReturnIfAttribute( bool parameterValue ) { }
+
+    public bool ParameterValue => default;
+}
+
+[AttributeUsage( AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Constructor | AttributeTargets.Event | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Struct, Inherited = false, AllowMultiple = false )]
+internal sealed class ExcludeFromCodeCoverageAttribute : Attribute { }
+
+[AttributeUsage( AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false )]
+internal sealed class MaybeNullAttribute : Attribute { }
+
+[AttributeUsage( AttributeTargets.Parameter )]
+internal sealed class MaybeNullWhenAttribute : Attribute
+{
+    public MaybeNullWhenAttribute( bool returnValue ) { }
+
+    public bool ReturnValue => default;
+}
+
+[AttributeUsage( AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false )]
+internal sealed class NotNullAttribute : Attribute { }
+
+[AttributeUsage( AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false )]
+internal sealed class NotNullIfNotNullAttribute : Attribute
+{
+    public NotNullIfNotNullAttribute( string parameterName ) { }
+
+    public string ParameterName => default!;
+}
+
+[AttributeUsage( AttributeTargets.Parameter )]
+internal sealed class NotNullWhenAttribute : Attribute
+{
+    public NotNullWhenAttribute( bool returnValue ) { }
+
+    public bool ReturnValue => default;
+}