Method to get source for each configuration element

src/Configuration/Config.Abstractions/src/ConfigurationRootExtensions.cs

@@ -0,0 +1,75 @@
+// 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.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Microsoft.Extensions.Configuration
+{
+    /// <summary>
+    /// Extension methods for <see cref="IConfigurationRoot"/>.
+    /// </summary>
+    public static class ConfigurationRootExtensions
+    {
+        /// <summary>
+        /// Generates a human-readable view of the configuration showing where each value came from.
+        /// </summary>
+        /// <returns> The debug view. </returns>
+        public static string GetDebugView(this IConfigurationRoot root)
+        {
+            void RecurseChildren(
+                StringBuilder stringBuilder,
+                IEnumerable<IConfigurationSection> children,
+                string indent)
+            {
+                foreach (var child in children)
+                {
+                    var valueAndProvider = GetValueAndProvider(root, child.Path);
+
+                    if (valueAndProvider.Provider != null)
+                    {
+                        stringBuilder
+                            .Append(indent)
+                            .Append(child.Key)
+                            .Append("=")
+                            .Append(valueAndProvider.Value)
+                            .Append(" (")
+                            .Append(valueAndProvider.Provider)
+                            .AppendLine(")");
+                    }
+                    else
+                    {
+                        stringBuilder
+                            .Append(indent)
+                            .Append(child.Key)
+                            .AppendLine(":");
+                    }
+
+                    RecurseChildren(stringBuilder, child.GetChildren(), indent + "  ");
+                }
+            }
+
+            var builder = new StringBuilder();
+
+            RecurseChildren(builder, root.GetChildren(), "");
+
+            return builder.ToString();
+        }
+
+        private static (string Value, IConfigurationProvider Provider) GetValueAndProvider(
+            IConfigurationRoot root,
+            string key)
+        {
+            foreach (var provider in root.Providers.Reverse())
+            {
+                if (provider.TryGet(key, out var value))
+                {
+                    return (value, provider);
+                }
+            }
+
+            return (null, null);
+        }
+    }
+}

src/Configuration/Config.Abstractions/src/IConfigurationProvider.cs

@@ -47,4 +47,4 @@ public interface IConfigurationProvider
         /// <returns>The child keys.</returns>
         IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string parentPath);
     }
-}
+}

src/Configuration/Config.Abstractions/src/IConfigurationRoot.cs

@@ -1,7 +1,6 @@
 // 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.
 
-using System;
 using System.Collections.Generic;
 
 namespace Microsoft.Extensions.Configuration

src/Configuration/Config.AzureKeyVault/test/ConfigurationProviderAzureKeyVaultTest.cs

@@ -14,6 +14,11 @@ namespace Microsoft.Extensions.Configuration.AzureKeyVault.Test
 {
     public class ConfigurationProviderKeyVaultTest : ConfigurationProviderTestBase
     {
+        public override void Null_values_are_included_in_the_config()
+        {
+            AssertConfig(BuildConfigRoot(LoadThroughProvider(TestSection.NullsTestConfig)), expectNulls: true);
+        }
+
         protected override (IConfigurationProvider Provider, System.Action Initializer) LoadThroughProvider(
             TestSection testConfig)
         {

src/Configuration/Config.EnvironmentVariables/test/ConfigurationProviderEnvironmentVariablesTest.cs

@@ -26,5 +26,10 @@ public override void Load_from_single_provider_with_differing_case_duplicates_th
         {
             AssertConfig(BuildConfigRoot(LoadThroughProvider(TestSection.DuplicatesDifferentCaseTestConfig)));
         }
+
+        public override void Null_values_are_included_in_the_config()
+        {
+            AssertConfig(BuildConfigRoot(LoadThroughProvider(TestSection.NullsTestConfig)), expectNulls: true);
+        }
     }
 }

src/Configuration/Config.FileExtensions/src/FileConfigurationProvider.cs

@@ -42,6 +42,13 @@ public FileConfigurationProvider(FileConfigurationSource source)
         /// The source settings for this provider.
         /// </summary>
         public FileConfigurationSource Source { get; }
+
+        /// <summary>
+        /// Generates a string representing this provider name and relevant details.
+        /// </summary>
+        /// <returns> The configuration name. </returns>
+        public override string ToString()
+            => $"{GetType().Name} for '{Source.Path}' ({(Source.Optional ? "Optional" : "Required")})";
 
         private void Load(bool reload)
         {

src/Configuration/Config.Json/test/ConfigurationProviderJsonTest.cs

@@ -35,13 +35,15 @@ protected override (IConfigurationProvider Provider, Action Initializer) LoadThr
 
         private void SectionToJson(StringBuilder jsonBuilder, TestSection section)
         {
+            string ValueToJson(object value) => value == null ? "null" : $"'{value}'";
+
             jsonBuilder.AppendLine("{");
 
             foreach (var tuple in section.Values)
             {
                 jsonBuilder.AppendLine(tuple.Value.AsArray != null
-                    ? $"'{tuple.Key}': [{string.Join(", ", tuple.Value.AsArray.Select(v => $"'{v}'"))}],"
-                    : $"'{tuple.Key}': '{tuple.Value.AsString}',");
+                    ? $"'{tuple.Key}': [{string.Join(", ", tuple.Value.AsArray.Select(ValueToJson))}],"
+                    : $"'{tuple.Key}': {ValueToJson(tuple.Value.AsString)},");
             }
 
             foreach (var tuple in section.Sections)

src/Configuration/Config.KeyPerFile/src/KeyPerFileConfigurationProvider.cs

@@ -39,10 +39,8 @@ public override void Load()
                 {
                     return;
                 }
-                else
-                {
-                    throw new DirectoryNotFoundException("A non-null file provider for the directory is required when this source is not optional.");
-                }
+
+                throw new DirectoryNotFoundException("A non-null file provider for the directory is required when this source is not optional.");
             }
 
             var directory = Source.FileProvider.GetDirectoryContents("/");
@@ -68,5 +66,15 @@ public override void Load()
                 }
             }
         }
+
+        private string GetDirectoryName()
+            => Source.FileProvider?.GetFileInfo("/")?.PhysicalPath ?? "<Unknown>";
+
+        /// <summary>
+        /// Generates a string representing this provider name and relevant details.
+        /// </summary>
+        /// <returns> The configuration name. </returns>
+        public override string ToString()
+            => $"{GetType().Name} for files in '{GetDirectoryName()}' ({(Source.Optional ? "Optional" : "Required")})";
     }
 }

src/Configuration/Config.KeyPerFile/test/KeyPerFileTests.cs

@@ -190,20 +190,11 @@ public TestFileProvider(params IFileInfo[] files)
             _contents = new TestDirectoryContents(files);
         }
 
-        public IDirectoryContents GetDirectoryContents(string subpath)
-        {
-            return _contents;
-        }
+        public IDirectoryContents GetDirectoryContents(string subpath) => _contents;
 
-        public IFileInfo GetFileInfo(string subpath)
-        {
-            throw new NotImplementedException();
-        }
+        public IFileInfo GetFileInfo(string subpath) => new TestFile("TestDirectory");
 
-        public IChangeToken Watch(string filter)
-        {
-            throw new NotImplementedException();
-        }
+        public IChangeToken Watch(string filter) => throw new NotImplementedException();
     }
 
     class TestDirectoryContents : IDirectoryContents
@@ -215,75 +206,33 @@ public TestDirectoryContents(params IFileInfo[] files)
             _list = new List<IFileInfo>(files);
         }
 
-        public bool Exists
-        {
-            get
-            {
-                return true;
-            }
-        }
+        public bool Exists => true;
 
-        public IEnumerator<IFileInfo> GetEnumerator()
-        {
-            return _list.GetEnumerator();
-        }
+        public IEnumerator<IFileInfo> GetEnumerator() => _list.GetEnumerator();
 
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return GetEnumerator();
-        }
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
     }
 
     //TODO: Probably need a directory and file type.
     class TestFile : IFileInfo
     {
-        private string _name;
-        private string _contents;
+        private readonly string _name;
+        private readonly string _contents;
 
-        public bool Exists
-        {
-            get
-            {
-                return true;
-            }
-        }
+        public bool Exists => true;
 
         public bool IsDirectory
         {
             get;
         }
 
-        public DateTimeOffset LastModified
-        {
-            get
-            {
-                throw new NotImplementedException();
-            }
-        }
+        public DateTimeOffset LastModified => throw new NotImplementedException();
 
-        public long Length
-        {
-            get
-            {
-                throw new NotImplementedException();
-            }
-        }
+        public long Length => throw new NotImplementedException();
 
-        public string Name
-        {
-            get
-            {
-                return _name;
-            }
-        }
+        public string Name => _name;
 
-        public string PhysicalPath
-        {
-            get
-            {
-                throw new NotImplementedException();
-            }
-        }
+        public string PhysicalPath => "Root/" + Name;
 
         public TestFile(string name)
         {
@@ -304,7 +253,9 @@ public Stream CreateReadStream()
                 throw new InvalidOperationException("Cannot create stream from directory");
             }
 
-            return new MemoryStream(Encoding.UTF8.GetBytes(_contents));
+            return _contents == null
+                ? new MemoryStream()
+                : new MemoryStream(Encoding.UTF8.GetBytes(_contents));
         }
     }
 }

src/Configuration/Config.Xml/test/ConfigurationProviderXmlTest.cs

@@ -10,11 +10,42 @@ namespace Microsoft.Extensions.Configuration.Xml.Test
 {
     public class ConfigurationProviderXmlTest : ConfigurationProviderTestBase
     {
+        public override void Combine_before_other_provider()
+        {
+            // Disabled test due to XML handling of empty section.
+        }
+
         public override void Combine_after_other_provider()
         {
             // Disabled test due to XML handling of empty section.
         }
 
+        public override void Has_debug_view()
+        {
+            var configRoot = BuildConfigRoot(LoadThroughProvider(TestSection.TestConfig));
+            var providerTag = configRoot.Providers.Single().ToString();
+
+            var expected =
+                $@"Key1=Value1 ({providerTag})
+Section1:
+  Key2=Value12 ({providerTag})
+  Section2:
+    Key3=Value123 ({providerTag})
+    Key3a:
+      0=ArrayValue0 ({providerTag})
+        Name=0 ({providerTag})
+      1=ArrayValue1 ({providerTag})
+        Name=1 ({providerTag})
+      2=ArrayValue2 ({providerTag})
+        Name=2 ({providerTag})
+Section3:
+  Section4:
+    Key4=Value344 ({providerTag})
+";
+
+            AssertDebugView(configRoot, expected);
+        }
+
         protected override (IConfigurationProvider Provider, Action Initializer) LoadThroughProvider(TestSection testConfig)
         {
             var xmlBuilder = new StringBuilder();
@@ -36,7 +67,7 @@ private void SectionToXml(StringBuilder xmlBuilder, string sectionName, TestSect
 
             foreach (var tuple in section.Values)
             {
-                if (tuple.Value.AsString != null)
+                if (tuple.Value.AsArray == null)
                 {
                     xmlBuilder.AppendLine($"<{tuple.Key}>{tuple.Value.AsString}</{tuple.Key}>");
                 }

src/Configuration/Config/src/ConfigurationProvider.cs

@@ -94,5 +94,11 @@ protected void OnReload()
             var previousToken = Interlocked.Exchange(ref _reloadToken, new ConfigurationReloadToken());
             previousToken.OnReload();
         }
+
+        /// <summary>
+        /// Generates a string representing this provider name and relevant details.
+        /// </summary>
+        /// <returns> The configuration name. </returns>
+        public override string ToString() => $"{GetType().Name}";
     }
 }

src/Configuration/Config/src/ConfigurationRoot.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public class ConfigurationRoot : IConfigurationRoot
     {
-        private IList<IConfigurationProvider> _providers;
+        private readonly IList<IConfigurationProvider> _providers;
         private ConfigurationReloadToken _changeToken = new ConfigurationReloadToken();
 
         /// <summary>
@@ -52,17 +52,14 @@ public string this[string key]
             {
                 foreach (var provider in _providers.Reverse())
                 {
-                    string value;
-
-                    if (provider.TryGet(key, out value))
+                    if (provider.TryGet(key, out var value))
                     {
                         return value;
                     }
                 }
 
                 return null;
             }
-
             set
             {
                 if (!_providers.Any())

src/Configuration/Config/src/ConfigurationRootExtension.cs → src/Configuration/Config/src/InternalConfigurationRootExtensions.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Extensions.Configuration
     /// <summary>
     /// Extensions method for <see cref="IConfigurationRoot"/>
     /// </summary>
-    internal static class ConfigurationRootExtension
+    internal static class InternalConfigurationRootExtensions
     {
         /// <summary>
         /// Gets the immediate children sub-sections of configuration root based on key.