Allow access to original IConfigurationProvider

Author: halter73

src/DefaultBuilder/src/ConfigurationProviderSource.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Primitives;
 
@@ -22,7 +23,7 @@ public IConfigurationProvider Build(IConfigurationBuilder builder)
 
         // These providers have already been loaded, so no need to reload initially.
         // Otherwise, providers that cannot be reloaded like StreamConfigurationProviders will fail.
-        private sealed class IgnoreFirstLoadConfigurationProvider : IConfigurationProvider, IDisposable
+        private sealed class IgnoreFirstLoadConfigurationProvider : IConfigurationProvider, IEnumerable<IConfigurationProvider>, IDisposable
         {
             private readonly IConfigurationProvider _provider;
 
@@ -64,6 +65,11 @@ public bool TryGet(string key, out string value)
                 return _provider.TryGet(key, out value);
             }
 
+            // Provide access to the original IConfigurationProvider via a single-element IEnumerable to code that goes out of its way to look for it.
+            public IEnumerator<IConfigurationProvider> GetEnumerator() => new List<IConfigurationProvider> { _provider }.GetEnumerator();
+
+            IEnumerator IEnumerable.GetEnumerator() => new List<IConfigurationProvider> { _provider }.GetEnumerator();
+
             public override bool Equals(object? obj)
             {
                 return _provider.Equals(obj);

src/DefaultBuilder/test/Microsoft.AspNetCore.Tests/WebApplicationTests.cs

@@ -756,6 +756,24 @@ public async Task WebApplicationDisposesConfigurationProvidersAddedInBuild()
             Assert.Equal(1, appConfigSource.ProvidersDisposed);
         }
 
+        [Fact]
+        public async Task WebApplicationMakesOriginalConfigurationProvidersAddedInBuildAccessable()
+        {
+            // This mimics what WebApplicationFactory<T> does and runs configure
+            // services callbacks
+            using var listener = new HostingListener(hostBuilder =>
+            {
+                hostBuilder.ConfigureAppConfiguration(config => config.Add(new RandomConfigurationSource()));
+            });
+
+            var builder = WebApplication.CreateBuilder();
+            await using var app = builder.Build();
+
+            var wrappedProviders = ((IConfigurationRoot)app.Configuration).Providers.OfType<IEnumerable<IConfigurationProvider>>();
+            var unwrappedProviders = wrappedProviders.Select(p => Assert.Single(p));
+            Assert.Single(unwrappedProviders.OfType<RandomConfigurationProvider>());
+        }
+
         [Fact]
         public void WebApplicationBuilderHostProperties_IsCaseSensitive()
         {