Handle nullable attributes on platforms that lack them

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>

diff --git a/src/System.Private.CoreLib/shared/System/Diagnostics/CodeAnalysis/NullableAttributes.cs b/src/System.Private.CoreLib/shared/System/Diagnostics/CodeAnalysis/NullableAttributes.cs
index 640ff8f..3770a5f 100644 (file)
--- a/src/System.Private.CoreLib/shared/System/Diagnostics/CodeAnalysis/NullableAttributes.cs
+++ b/src/System.Private.CoreLib/shared/System/Diagnostics/CodeAnalysis/NullableAttributes.cs
@@ -6,23 +6,48 @@ 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)]
-    public sealed class AllowNullAttribute : Attribute { }
+#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)]
-    public sealed class DisallowNullAttribute : Attribute { }
+#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)]
-    public sealed class MaybeNullAttribute : Attribute { }
+#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)]
-    public sealed class NotNullAttribute : Attribute { }
+#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)]
-    public sealed class MaybeNullWhenAttribute : Attribute
+#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">
@@ -36,7 +61,12 @@ namespace System.Diagnostics.CodeAnalysis
 
     /// <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)]
-    public sealed class NotNullWhenAttribute : Attribute
+#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">
@@ -50,7 +80,12 @@ namespace System.Diagnostics.CodeAnalysis
 
     /// <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)]
-    public sealed class NotNullIfNotNullAttribute : Attribute
+#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">
@@ -64,11 +99,21 @@ namespace System.Diagnostics.CodeAnalysis
 
     /// <summary>Applied to a method that will never return under any circumstance.</summary>
     [AttributeUsage(AttributeTargets.Method, Inherited = false)]
-    public sealed class DoesNotReturnAttribute : Attribute { }
+#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)]
-    public sealed class DoesNotReturnIfAttribute : Attribute
+#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">