Fix Configuration to ensure calling the property setters.

src/libraries/Microsoft.Extensions.Configuration.Binder/src/ConfigurationBinder.cs

@@ -262,7 +262,10 @@ private static void BindProperty(PropertyInfo property, object instance, IConfig
                 config.GetSection(GetPropertyName(property)),
                 options);
 
-            if (propertyBindingPoint.HasNewValue)
+            // For property binding, there are some cases when HasNewValue is not set in BindingPoint while a non-null Value inside that object can be retrieved from the property getter.
+            // As example, when binding a property which not having a configuration entry matching this property and the getter can initialize the Value.
+            // It is important to call the property setter as the setters can have a logic adjusting the Value.
+            if (!propertyBindingPoint.IsReadOnly && propertyBindingPoint.Value is not null)
             {
                 property.SetValue(instance, propertyBindingPoint.Value);
             }

src/libraries/Microsoft.Extensions.Configuration.Binder/tests/ConfigurationBinderTests.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Configuration.Test;
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -2733,6 +2735,61 @@ public void CanBindPrivatePropertiesFromBaseClass()
             Assert.Equal("a", test.ExposePrivatePropertyValue());
         }
 
+        [Fact]
+        public void EnsureCallingThePropertySetter()
+        {
+            var json = @"{
+                ""IPFiltering"": {
+                    ""HttpStatusCode"": 401,
+                    ""Blacklist"": [ ""192.168.0.10-192.168.10.20"", ""fe80::/10"" ]
+                }
+            }";
+
+            var configuration = new ConfigurationBuilder()
+                .AddJsonStream(TestStreamHelpers.StringToStream(json))
+                .Build();
+
+            OptionWithCollectionProperties options = configuration.GetSection("IPFiltering").Get<OptionWithCollectionProperties>();
+
+            Assert.NotNull(options);
+            Assert.Equal(2, options.Blacklist.Count);
+            Assert.Equal("192.168.0.10-192.168.10.20", options.Blacklist.ElementAt(0));
+            Assert.Equal("fe80::/10", options.Blacklist.ElementAt(1));
+
+            Assert.Equal(2, options.ParsedBlacklist.Count); // should be initialized when calling the options.Blacklist setter.
+
+            Assert.Equal(401, options.HttpStatusCode); // exists in configuration and properly sets the property
+            Assert.Equal(2, options.OtherCode); // doesn't exist in configuration. the setter sets default value '2'
+        }
+
+        public class OptionWithCollectionProperties
+        {
+            private int _otherCode;
+            private ICollection<string> blacklist = new HashSet<string>();
+
+            public ICollection<string> Blacklist
+            {
+                get => this.blacklist;
+                set
+                {
+                    this.blacklist = value ?? new HashSet<string>();
+                    this.ParsedBlacklist = this.blacklist.Select(b => b).ToList();
+                }
+            }
+
+            public int HttpStatusCode { get; set; } = 0;
+
+            // ParsedBlacklist initialized using the setter of Blacklist.
+            public ICollection<string> ParsedBlacklist { get; private set; } = new HashSet<string>();
+
+            // This property not having any match in the configuration. Still the setter need to be called during the binding.
+            public int OtherCode
+            {
+                get => _otherCode;
+                set => _otherCode = value == 0 ? 2 : value;
+            }
+        }
+
         private interface ISomeInterface
         {
         }

src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Microsoft.Extensions.Configuration.Binder.Tests.csproj

@@ -10,13 +10,14 @@
              Link="Common\ConfigurationProviderExtensions.cs" />
     <Compile Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\tests\Common\TestStreamHelpers.cs"
              Link="Common\TestStreamHelpers.cs" />
-    <Compile Include="$(CoreLibSharedDir)System\Runtime\CompilerServices\IsExternalInit.cs" Link="Common\System\Runtime\CompilerServices\IsExternalInit.cs" /> 
+    <Compile Include="$(CoreLibSharedDir)System\Runtime\CompilerServices\IsExternalInit.cs" Link="Common\System\Runtime\CompilerServices\IsExternalInit.cs" />
 
     <TrimmerRootDescriptor Include="$(MSBuildThisFileDirectory)ILLink.Descriptors.xml" />
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\src\Microsoft.Extensions.Configuration.Json.csproj" SkipUseReferenceAssembly="true" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" SkipUseReferenceAssembly="true" />
     <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.Binder.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>