Fix config binder source generator emitting invalid tuple instantiation code

src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Specs/BindingHelperInfo.cs

@@ -173,6 +173,14 @@ bool TryRegisterCore()
                                 {
                                     foreach (PropertySpec property in objectSpec.Properties!)
                                     {
+                                        // Skip types reachable only through non-bindable properties, unless the
+                                        // property backs a constructor parameter. Constructor parameters are always
+                                        // bound in the Initialize method, so their types must still be registered.
+                                        if (!_typeIndex.ShouldBindTo(property) && property.MatchingCtorParam is null)
+                                        {
+                                            continue;
+                                        }
+
                                         TryRegisterTransitiveTypesForMethodGen(property.TypeRef);
 
                                         if (_typeIndex.GetTypeSpec(property.TypeRef) is ComplexTypeSpec)

src/libraries/Microsoft.Extensions.Configuration.Binder/tests/SourceGenerationTests/GeneratorTests.cs

@@ -349,6 +349,152 @@ public static void Main()
             AssertCanCreateAssemblyImage(result.OutputCompilation);
         }
 
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNetCore))]
+        public async Task ListOfTupleWithComplexElementInInternalPropertyTest()
+        {
+            string source = """
+                using Microsoft.Extensions.Configuration;
+                using System;
+                using System.Collections.Generic;
+
+                public class Program
+                {
+                    public static void Main()
+                    {
+                        ConfigurationBuilder configurationBuilder = new();
+                        IConfiguration config = configurationBuilder.Build();
+                        ExampleOptions options = new();
+                        config.Bind(options);
+                    }
+                }
+
+                public class ExampleOptions
+                {
+                    public List<string> ExampleCollection { get; set; } = new();
+
+                    internal List<(string, ICollection<string>?)> UsesCollection =>
+                        [
+                            ("Label-1", ExampleCollection)
+                        ];
+                }
+                """;
+
+            ConfigBindingGenRunResult result = await RunGeneratorAndUpdateCompilation(source, assemblyReferences: GetAssemblyRefsWithAdditional(typeof(ConfigurationBuilder), typeof(List<>)));
+            Assert.NotNull(result.GeneratedSource);
+            Assert.Empty(result.Diagnostics);
+
+            AssertCanCreateAssemblyImage(result.OutputCompilation);
+        }
+
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNetCore))]
+        [InlineData("IReadOnlyList")]
+        [InlineData("IReadOnlyCollection")]
+        [InlineData("IReadOnlySet")]
+        [InlineData("IEnumerable")]
+        public async Task ReadOnlyCollectionConstructorParameterIsBindable(string collectionType)
+        {
+            string source = $$"""
+                using Microsoft.Extensions.Configuration;
+                using System.Collections.Generic;
+
+                public class Program
+                {
+                    public static void Main()
+                    {
+                        ConfigurationBuilder configurationBuilder = new();
+                        IConfiguration config = configurationBuilder.Build();
+                        Options options = config.Get<Options>();
+                    }
+                }
+
+                public record Options(string Name, {{collectionType}}<string> Values);
+                """;
+
+            ConfigBindingGenRunResult result = await RunGeneratorAndUpdateCompilation(source, assemblyReferences: GetAssemblyRefsWithAdditional(typeof(ConfigurationBuilder), typeof(List<>)));
+            Assert.NotNull(result.GeneratedSource);
+            Assert.Empty(result.Diagnostics);
+
+            // The collection type is only reachable through a read-only property, so its BindCore
+            // helper must still be generated for the constructor parameter.
+            AssertCanCreateAssemblyImage(result.OutputCompilation);
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNetCore))]
+        public async Task ComplexReadOnlyListConstructorParameterIsBindable()
+        {
+            string source = """
+                using Microsoft.Extensions.Configuration;
+                using System.Collections.Generic;
+
+                public class Program
+                {
+                    public static void Main()
+                    {
+                        ConfigurationBuilder configurationBuilder = new();
+                        IConfiguration config = configurationBuilder.Build();
+                        Options options = config.Get<Options>();
+                    }
+                }
+
+                public class Child
+                {
+                    public string Value { get; set; }
+                }
+
+                public record Options(string Name, IReadOnlyList<Child> Items);
+                """;
+
+            ConfigBindingGenRunResult result = await RunGeneratorAndUpdateCompilation(source, assemblyReferences: GetAssemblyRefsWithAdditional(typeof(ConfigurationBuilder), typeof(List<>)));
+            Assert.NotNull(result.GeneratedSource);
+            Assert.Empty(result.Diagnostics);
+
+            AssertCanCreateAssemblyImage(result.OutputCompilation);
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNetCore))]
+        public async Task TypeReachableOnlyThroughNonBindablePropertyIsNotEmitted()
+        {
+            string source = """
+                using Microsoft.Extensions.Configuration;
+                using System.Collections.Generic;
+
+                public class Program
+                {
+                    public static void Main()
+                    {
+                        ConfigurationBuilder configurationBuilder = new();
+                        IConfiguration config = configurationBuilder.Build();
+                        ExampleOptions options = new();
+                        config.Bind(options);
+                    }
+                }
+
+                public class ExampleOptions
+                {
+                    public List<string> ExampleCollection { get; set; } = new();
+
+                    // Non-bindable internal property. UnreachableChild is only reachable through it,
+                    // so the generator must not emit any binding code that references it.
+                    internal List<UnreachableChild> UsesCollection => new();
+                }
+
+                public class UnreachableChild
+                {
+                    public string Value { get; set; }
+                }
+                """;
+
+            ConfigBindingGenRunResult result = await RunGeneratorAndUpdateCompilation(source, assemblyReferences: GetAssemblyRefsWithAdditional(typeof(ConfigurationBuilder), typeof(List<>)));
+            Assert.NotNull(result.GeneratedSource);
+            Assert.Empty(result.Diagnostics);
+
+            // The type is reachable only through a non-bindable property, so the generator must
+            // not register or emit any binding code that references it.
+            Assert.DoesNotContain("UnreachableChild", result.GeneratedSource.Value.SourceText.ToString());
+
+            AssertCanCreateAssemblyImage(result.OutputCompilation);
+        }
+
         [Fact]
         public async Task BindingToCollectionOnlyTest()
         {