Optimize the performance of InternalConfigurationRootExtensions.GetChildrenImplementation

src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs

@@ -60,6 +60,10 @@ public partial interface IConfigurationBuilder
     public partial interface IConfigurationProvider
     {
         System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string? parentPath);
+#if NET7_0_OR_GREATER
+        System.Collections.Generic.IEnumerable<string> GetChildKeys(string? parentPath)
+            => GetChildKeys(System.Linq.Enumerable.Empty<string>(), parentPath);
+#endif
         Microsoft.Extensions.Primitives.IChangeToken GetReloadToken();
         void Load();
         void Set(string key, string? value);

src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs

@@ -46,5 +46,16 @@ public interface IConfigurationProvider
         /// <param name="parentPath">The parent path.</param>
         /// <returns>The child keys.</returns>
         IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath);
+
+#if NET7_0_OR_GREATER
+        /// <summary>
+        /// Returns the configuration keys for a given parent path based on this
+        /// <see cref="IConfigurationProvider"/> data.
+        /// </summary>
+        /// <param name="parentPath">The parent path.</param>
+        /// <returns>The child keys.</returns>
+        IEnumerable<string> GetChildKeys(string? parentPath)
+            => GetChildKeys(System.Linq.Enumerable.Empty<string>(), parentPath);
+#endif
     }
 }

src/libraries/Microsoft.Extensions.Configuration/src/InternalConfigurationRootExtensions.cs

@@ -24,11 +24,15 @@ internal static IEnumerable<IConfigurationSection> GetChildrenImplementation(thi
             IEnumerable<IConfigurationProvider> providers = reference?.Providers ?? root.Providers;
 
             IEnumerable<IConfigurationSection> children = providers
+#if NET7_0_OR_GREATER
+                .SelectMany(p => p.GetChildKeys(path))
+                .OrderBy(key => key, ConfigurationKeyComparer.Instance)
+#else
                 .Aggregate(Enumerable.Empty<string>(),
                     (seed, source) => source.GetChildKeys(seed, path))
+#endif
                 .Distinct(StringComparer.OrdinalIgnoreCase)
                 .Select(key => root.GetSection(path == null ? key : ConfigurationPath.Combine(path, key)));
-
             if (reference is null)
             {
                 return children;

src/libraries/Microsoft.Extensions.Configuration/tests/ConfigurationTest.cs

@@ -971,5 +971,145 @@ public void ProviderWithNullReloadToken()
             // Assert
             Assert.NotNull(config);
         }
+
+        [Fact]
+        public void ConfigurationGetChildrenKeysOrdered()
+        {
+            // Arrange
+            var dic1 = new Dictionary<string, string>()
+            {
+                {"Services:2", "Service2"}
+            };
+            var dic2 = new Dictionary<string, string>()
+            {
+                {"Services:10", "Service10"},
+            };
+            var memConfigSrc1 = new MemoryConfigurationSource { InitialData = dic1 };
+            var memConfigSrc2 = new MemoryConfigurationSource { InitialData = dic2 };
+
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.Add(memConfigSrc1);
+            configurationBuilder.Add(memConfigSrc2);
+
+            var config = configurationBuilder.Build();
+
+            // Act
+            var keys = config.GetSection("Services").GetChildren().Select(c => c.Key).ToList();
+
+            // Assert
+            Assert.Equal(2, keys.Count);
+            Assert.Equal("2", keys[0]);
+            Assert.Equal("10", keys[1]);
+        }
+
+        [Theory]
+        [ClassData(typeof(OverrideGetChildKeysConfigurationProviders))]
+        public void ConfigurationGetChildrenNotOptimizedConfigurationProvider(IConfigurationProvider provider)
+        {
+            // Arrange
+            var dic2 = new Dictionary<string, string>()
+            {
+                {"key2", "val"},
+            };
+            var src1 = new FixedProviderConfigurationSource(provider);
+            var memConfigSrc2 = new MemoryConfigurationSource { InitialData = dic2 };
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.Add(src1);
+            configurationBuilder.Add(memConfigSrc2);
+            var configSorted = configurationBuilder.Build();
+            configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.Add(memConfigSrc2);
+            configurationBuilder.Add(src1);
+            var configNotSorted = configurationBuilder.Build();
+
+            // Act
+            var keysSorted = configSorted.GetChildren().Select(c => c.Key).ToList();
+            var keysNotSorted = configNotSorted.GetChildren().Select(c => c.Key).ToList();
+
+            // Assert
+            Assert.Equal(3, keysSorted.Count);
+            Assert.Equal(3, keysNotSorted.Count);
+
+            // The keys should be sorted by the 2nd IConfigurationProvider
+            // because it inherits from helper class ConfigurationProvider.
+            Assert.Equal("key1", keysSorted[0]);
+            Assert.Equal("key2", keysSorted[1]);
+            Assert.Equal("key3", keysSorted[2]);
+
+            // Actually here is a breaking change!
+            // previously the order is controlled by the last provider
+            // now the order is controalled in GetChildrenImplementation, which is always sorted
+#if !NET7_0_OR_GREATER
+            Assert.Equal("key2", keysNotSorted[0]);
+            Assert.Equal("key3", keysNotSorted[1]);
+            Assert.Equal("key1", keysNotSorted[2]);
+#endif
+        }
+
+        private class OverrideGetChildKeysConfigurationProviders : TheoryData<IConfigurationProvider>
+        {
+            public OverrideGetChildKeysConfigurationProviders()
+            {
+                Add(new InheritHelperClassButOverrideMethodGetChildKeysConfigurationProvider());
+                Add(new NotInheritHelperClassConfigurationProvider());
+            }
+
+            public static IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath)
+            {
+                if (parentPath != null)
+                {
+                    throw new ArgumentException("Not support parentPath");
+                }
+
+                foreach (var key in earlierKeys)
+                {
+                    yield return key;
+                }
+
+                // For the IConfigurationProvider implementation that not inherit from helper class ConfigurationProvider,
+                // the returned keys might not be sorted.
+                yield return "key3";
+                yield return "key1";
+            }
+        }
+
+        private class FixedProviderConfigurationSource : IConfigurationSource
+        {
+            private readonly IConfigurationProvider provider;
+            public FixedProviderConfigurationSource(IConfigurationProvider provider)
+            {
+                this.provider = provider;
+            }
+
+            public IConfigurationProvider Build(IConfigurationBuilder builder) => provider;
+        }
+
+        private class InheritHelperClassButOverrideMethodGetChildKeysConfigurationProvider : ConfigurationProvider
+        {
+            public override IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath)
+                => OverrideGetChildKeysConfigurationProviders.GetChildKeys(earlierKeys, parentPath);
+        }
+
+        private class NotInheritHelperClassConfigurationProvider : IConfigurationProvider
+        {
+            public IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath)
+                => OverrideGetChildKeysConfigurationProviders.GetChildKeys(earlierKeys, parentPath);
+
+            public Primitives.IChangeToken GetReloadToken() => new ConfigurationReloadToken();
+
+            public void Load()
+            {
+            }
+
+            public void Set(string key, string? value)
+            {
+            }
+
+            public bool TryGet(string key, out string? value)
+            {
+                value = "val";
+                return true;
+            }
+        }
     }
 }