Add MaybeNullWhen( attribute to IParsable.TryParse / ISpanParsable.TryParse (#71381)

src/libraries/System.Private.CoreLib/src/System/IParsable.cs

@@ -24,6 +24,6 @@ public interface IParsable<TSelf>
         /// <param name="provider">An object that provides culture-specific formatting information about <paramref name="s" />.</param>
         /// <param name="result">On return, contains the result of succesfully parsing <paramref name="s" /> or an undefined value on failure.</param>
         /// <returns><c>true</c> if <paramref name="s" /> was successfully parsed; otherwise, <c>false</c>.</returns>
-        static abstract bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, out TSelf result);
+        static abstract bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, [MaybeNullWhen(returnValue: false)] out TSelf result);
     }
 }

src/libraries/System.Private.CoreLib/src/System/ISpanParsable.cs

 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System
 {
     /// <summary>Defines a mechanism for parsing a span of characters to a value.</summary>
@@ -21,6 +23,6 @@ public interface ISpanParsable<TSelf> : IParsable<TSelf>
         /// <param name="provider">An object that provides culture-specific formatting information about <paramref name="s" />.</param>
         /// <param name="result">On return, contains the result of succesfully parsing <paramref name="s" /> or an undefined value on failure.</param>
         /// <returns><c>true</c> if <paramref name="s" /> was successfully parsed; otherwise, <c>false</c>.</returns>
-        static abstract bool TryParse(ReadOnlySpan<char> s, IFormatProvider? provider, out TSelf result);
+        static abstract bool TryParse(ReadOnlySpan<char> s, IFormatProvider? provider, [MaybeNullWhen(returnValue: false)] out TSelf result);
     }
 }

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -3805,7 +3805,7 @@ public partial interface IObserver<in T>
     public partial interface IParsable<TSelf> where TSelf : System.IParsable<TSelf>
     {
         static abstract TSelf Parse(string s, System.IFormatProvider? provider);
-        static abstract bool TryParse([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] string? s, System.IFormatProvider? provider, out TSelf result);
+        static abstract bool TryParse([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] string? s, System.IFormatProvider? provider, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TSelf result);
     }
     public partial interface IProgress<in T>
     {
@@ -3818,7 +3818,7 @@ public partial interface ISpanFormattable : System.IFormattable
     public partial interface ISpanParsable<TSelf> : System.IParsable<TSelf> where TSelf : System.ISpanParsable<TSelf>
     {
         static abstract TSelf Parse(System.ReadOnlySpan<char> s, System.IFormatProvider? provider);
-        static abstract bool TryParse(System.ReadOnlySpan<char> s, System.IFormatProvider? provider, out TSelf result);
+        static abstract bool TryParse(System.ReadOnlySpan<char> s, System.IFormatProvider? provider, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TSelf result);
     }
     public partial class Lazy<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>
     {