Method to get source for each configuration element

Fixes #609 by allowing the configuration paths to be associated with values to help with debugging.

Author: ajcvickers

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

@@ -68,5 +68,12 @@ public override void Load()
                 }
             }
         }
+
+        /// <summary>
+        /// Generates a string representing this provider name and relevant details.
+        /// </summary>
+        /// <returns> The configuration name. </returns>
+        public override string ToString()
+            => $"{GetType().Name} ({(Source.Optional ? "Optional" : "Required")})";
     }
 }

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

@@ -304,7 +304,9 @@ 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}>");
                 }