Add nullable annotations to Microsoft.AspNetCore.Components (#22944)

* Add nullable for Microsoft.AspNetCore.Components
Contributes to #5680

* Fixup

Author: pranavkm

src/Components/Components/ref/Microsoft.AspNetCore.Components.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(DefaultNetCoreTargetFramework)</TargetFrameworks>
     <TargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true'">$(DefaultNetCoreTargetFramework)</TargetFrameworks>
+    <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="Microsoft.AspNetCore.Components.netstandard2.0.cs" />

src/Components/Components/ref/Microsoft.AspNetCore.Components.netcoreapp.cs

@@ -18,7 +18,7 @@ public sealed class BindElementAttribute : Attribute
         /// <param name="suffix">The suffix value. For example, set this to <c>value</c> for <c>bind-value</c>, or set this to <see langword="null" /> for <c>bind</c>.</param>
         /// <param name="valueAttribute">The name of the value attribute to be bound.</param>
         /// <param name="changeAttribute">The name of an attribute that will register an associated change event.</param>
-        public BindElementAttribute(string element, string suffix, string valueAttribute, string changeAttribute)
+        public BindElementAttribute(string element, string? suffix, string valueAttribute, string changeAttribute)
         {
             if (element == null)
             {
@@ -38,6 +38,7 @@ public BindElementAttribute(string element, string suffix, string valueAttribute
             Element = element;
             ValueAttribute = valueAttribute;
             ChangeAttribute = changeAttribute;
+            Suffix = suffix;
         }
 
         /// <summary>
@@ -49,7 +50,7 @@ public BindElementAttribute(string element, string suffix, string valueAttribute
         /// Gets the suffix value.
         /// For example, this will be <c>value</c> to mean <c>bind-value</c>, or <see langword="null" /> to mean <c>bind</c>.
         /// </summary>
-        public string Suffix { get; }
+        public string? Suffix { get; }
 
         /// <summary>
         /// Gets the name of the value attribute to be bound.

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -22,6 +22,6 @@ public sealed class CascadingParameterAttribute : Attribute
         /// <see cref="CascadingValue{T}"/>  that supplies a value with a compatible
         /// type.
         /// </summary>
-        public string Name { get; set; }
+        public string? Name { get; set; }
     }
 }

src/Components/Components/src/BindConverter.cs

@@ -30,14 +30,14 @@ public static IReadOnlyList<CascadingParameterState> FindCascadingParameters(Com
             var infos = GetReflectedCascadingParameterInfos(componentType);
 
             // For components known not to have any cascading parameters, bail out early
-            if (infos == null)
+            if (infos.Length == 0)
             {
-                return null;
+                return Array.Empty<CascadingParameterState>();
             }
 
             // Now try to find matches for each of the cascading parameters
             // Defer instantiation of the result list until we know there's at least one
-            List<CascadingParameterState> resultStates = null;
+            List<CascadingParameterState>? resultStates = null;
 
             var numInfos = infos.Length;
             for (var infoIndex = 0; infoIndex < numInfos; infoIndex++)
@@ -56,10 +56,10 @@ public static IReadOnlyList<CascadingParameterState> FindCascadingParameters(Com
                 }
             }
 
-            return resultStates;
+            return resultStates ?? (IReadOnlyList<CascadingParameterState>)Array.Empty<CascadingParameterState>();
         }
 
-        private static ICascadingValueComponent GetMatchingCascadingValueSupplier(in ReflectedCascadingParameterInfo info, ComponentState componentState)
+        private static ICascadingValueComponent? GetMatchingCascadingValueSupplier(in ReflectedCascadingParameterInfo info, ComponentState componentState)
         {
             do
             {
@@ -89,7 +89,7 @@ private static ReflectedCascadingParameterInfo[] GetReflectedCascadingParameterI
 
         private static ReflectedCascadingParameterInfo[] CreateReflectedCascadingParameterInfos(Type componentType)
         {
-            List<ReflectedCascadingParameterInfo> result = null;
+            List<ReflectedCascadingParameterInfo>? result = null;
             var candidateProps = ComponentProperties.GetCandidateBindableProperties(componentType);
             foreach (var prop in candidateProps)
             {
@@ -108,17 +108,17 @@ private static ReflectedCascadingParameterInfo[] CreateReflectedCascadingParamet
                 }
             }
 
-            return result?.ToArray();
+            return result?.ToArray() ?? Array.Empty<ReflectedCascadingParameterInfo>();
         }
 
         readonly struct ReflectedCascadingParameterInfo
         {
             public string ConsumerValueName { get; }
-            public string SupplierValueName { get; }
+            public string? SupplierValueName { get; }
             public Type ValueType { get; }
 
             public ReflectedCascadingParameterInfo(
-                string consumerValueName, Type valueType, string supplierValueName)
+                string consumerValueName, Type valueType, string? supplierValueName)
             {
                 ConsumerValueName = consumerValueName;
                 SupplierValueName = supplierValueName;

src/Components/Components/src/BindElementAttribute.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+#nullable disable warnings
+
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
@@ -34,7 +36,7 @@ public class CascadingValue<TValue> : ICascadingValueComponent, IComponent
         /// If no name is specified, then descendant components will receive the
         /// value based the type of value they are requesting.
         /// </summary>
-        [Parameter] public string Name { get; set; }
+        [Parameter] public string? Name { get; set; }
 
         /// <summary>
         /// If true, indicates that <see cref="Value"/> will not change. This is a

src/Components/Components/src/CascadingParameterAttribute.cs

@@ -17,8 +17,8 @@ public static bool MayHaveChanged<T1, T2>(T1 oldValue, T2 newValue)
             }
             else if (oldIsNotNull) // i.e., both are not null (considering previous check)
             {
-                var oldValueType = oldValue.GetType();
-                var newValueType = newValue.GetType();
+                var oldValueType = oldValue!.GetType();
+                var newValueType = newValue!.GetType();
                 if (oldValueType != newValueType            // Definitely different
                     || !IsKnownImmutableType(oldValueType)  // Maybe different
                     || !oldValue.Equals(newValue))          // Somebody says they are different

src/Components/Components/src/CascadingParameterState.cs

@@ -13,7 +13,6 @@ public class ChangeEventArgs : EventArgs
         /// <summary>
         /// Gets or sets the new value.
         /// </summary>
-        public object Value { get; set; }
-
+        public object? Value { get; set; }
     }
 }