Enable binding of IConfiguration/IConfigurationSection

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

@@ -82,6 +82,7 @@ private static void BindProperty(PropertyInfo property, object instance, IConfig
             }
 
             propertyValue = BindInstance(property.PropertyType, propertyValue, config.GetSection(property.Name));
+
             if (propertyValue != null && hasPublicSetter)
             {
                 property.SetValue(instance, propertyValue);
@@ -90,6 +91,12 @@ private static void BindProperty(PropertyInfo property, object instance, IConfig
 
         private static object BindInstance(Type type, object instance, IConfiguration config)
         {
+            // if binding IConfigurationSection, break early
+            if (type == typeof(IConfigurationSection))
+            {
+                return config;
+            }
+
             var section = config as IConfigurationSection;
             var configValue = section?.Value;
             if (configValue != null)

test/Microsoft.Extensions.Configuration.Binder.Test/ConfigurationBinderTests.cs

@@ -6,6 +6,7 @@
 using System.ComponentModel;
 using System.Reflection;
 using Microsoft.Extensions.Configuration.Memory;
+using Microsoft.Extensions.Primitives;
 using Xunit;
 
 namespace Microsoft.Extensions.Configuration.Binder.Test
@@ -73,6 +74,86 @@ public class GenericOptions<T>
             public T Value { get; set; }
         }
 
+        public class ConfigurationInterfaceOptions
+        {
+            public IConfigurationSection Section { get; set; }
+        }                
+
+        public class DerivedOptionsWithIConfigurationSection : DerivedOptions
+        {
+            public IConfigurationSection DerivedSection { get; set; }
+        }
+
+        [Fact]
+        public void CanBindIConfigurationSection()
+        {
+            var dic = new Dictionary<string, string>
+            {
+                {"Section:Integer", "-2"},
+                {"Section:Boolean", "TRUe"},
+                {"Section:Nested:Integer", "11"},
+                {"Section:Virtual", "Sup"}
+            };
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.AddInMemoryCollection(dic);
+            var config = configurationBuilder.Build();
+
+            var options = new ConfigurationInterfaceOptions();
+            config.Bind(options);
+
+            var childOptions = new DerivedOptions();
+            options.Section.Bind(childOptions);
+
+            Assert.True(childOptions.Boolean);
+            Assert.Equal(-2, childOptions.Integer);
+            Assert.Equal(11, childOptions.Nested.Integer);
+            Assert.Equal("Derived:Sup", childOptions.Virtual);
+
+            Assert.Equal("Section", options.Section.Key);
+            Assert.Equal("Section", options.Section.Path);
+            Assert.Equal(null, options.Section.Value);
+        }
+
+        [Fact]
+        public void CanBindIConfigurationSectionWithDerivedOptionsSection()
+        {
+            var dic = new Dictionary<string, string>
+            {
+                {"Section:Integer", "-2"},
+                {"Section:Boolean", "TRUe"},
+                {"Section:Nested:Integer", "11"},
+                {"Section:Virtual", "Sup"},
+                {"Section:DerivedSection:Nested:Integer", "11"},
+                {"Section:DerivedSection:Virtual", "Sup"}
+            };
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.AddInMemoryCollection(dic);
+            var config = configurationBuilder.Build();
+
+            var options = new ConfigurationInterfaceOptions();
+            config.Bind(options);
+
+            var childOptions = new DerivedOptionsWithIConfigurationSection();
+            options.Section.Bind(childOptions);
+
+
+            var childDerivedOptions = new DerivedOptions();
+            childOptions.DerivedSection.Bind(childDerivedOptions);
+
+            Assert.True(childOptions.Boolean);
+            Assert.Equal(-2, childOptions.Integer);
+            Assert.Equal(11, childOptions.Nested.Integer);
+            Assert.Equal("Derived:Sup", childOptions.Virtual);
+            Assert.Equal(11, childDerivedOptions.Nested.Integer);
+            Assert.Equal("Derived:Sup", childDerivedOptions.Virtual);
+
+            Assert.Equal("Section", options.Section.Key);
+            Assert.Equal("Section", options.Section.Path);
+            Assert.Equal("DerivedSection", childOptions.DerivedSection.Key);
+            Assert.Equal("Section:DerivedSection", childOptions.DerivedSection.Path);
+            Assert.Equal(null, options.Section.Value);
+        }
+
         [Fact]
         public void GetScalarNullable()
         {