[release/10.0] Fixed codegen for IEnumerable<T> binding (#123422) (#123720)

github-actions[bot] · Dmitry Kandiner · web-flow · commit 42440b5b38bd · 2026-01-28T15:52:52.000-08:00
Backport of #123663 to release/10.0 /cc @tarekgh @dmitry-kandiner ## Customer Impact - [x] Customer reported - [ ] Found internally Using configuration source generator, when a user binds configuration to a class or record with a primary constructor, and one of the constructor parameters is exact of type `IEnumerable<T>`, the binding throws a `System.InvalidOperationException`, even though the binding is expected to succeed. The issue #123422 shows the customer report and more details. ## Regression - [x] Yes - [ ] No This is a regression in .NET 10.0.1. A previous servicing fix addressed several crashes, but one case was missed. That omission surfaced as this regression. The change that introduced the regression is #121325. ## Testing Manually verified the failing scenario and confirmed the fix resolves the issue. Added a regression test covering the previously failing case and ran the full test suite successfully. Reviewed related code paths to ensure no additional cases were missed. ## Risk Low, the change is targeting the specific case with specific type. The fix is localized to the failing scenario. --------- Signed-off-by: Dmitry Kandiner <dkandiner@growings.com> Co-authored-by: Dmitry Kandiner <dkandiner@growings.com>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Emitter/CoreBindingHelpers.cs b/src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Emitter/CoreBindingHelpers.cs
@@ -413,8 +413,9 @@ void EmitBindImplForMember(MemberSpec member)
                         if (member is ParameterSpec parameter && parameter.ErrorOnFailedBinding)
                         {
                             // Add exception logic for parameter ctors; must be present in configuration object.
-                            // In case of Arrays, we emit extra block to handle empty arrays. The throw block will not be `else` case at that time.
-                            EmitThrowBlock(condition: _typeIndex.GetEffectiveTypeSpec(member.TypeRef) is ArraySpec ? $"if ({member.Name} is null)" : "else");
+                            // In case of Arrays and IEnumerable<T>, we emit extra block to handle collection. The throw block will not be `else` case at that time.
+                            TypeSpec typeSpec = _typeIndex.GetEffectiveTypeSpec(member.TypeRef);
+                            EmitThrowBlock(condition: typeSpec is ArraySpec || typeSpec.IsExactIEnumerableOfT ? $"if ({member.Name} is null)" : "else");
                         }
 
                         _writer.WriteLine();
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.TestClasses.cs b/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.TestClasses.cs
@@ -1184,5 +1184,11 @@ public class MyOptionsWithNullableEnumerable
             public IEnumerable<int>? IEnumerableProperty { get; set; }
             public string[] StringArray { get; set; }
         }
+
+        internal sealed record ContainingIEnumerable
+        {
+            public NestedWithIEnumerable? Source { get; set; }
+        }
+        internal sealed record NestedWithIEnumerable(string Name, IEnumerable<string> Addresses);
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.cs b/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.cs
@@ -3060,5 +3060,29 @@ public void TestBindingEmptyArrayToNullIEnumerable()
             Assert.Equal(Array.Empty<int>(), result.IEnumerableProperty);
             Assert.Equal(Array.Empty<string>(), result.StringArray);
         }
+
+        [Fact]
+        public void TestBindingNestedIEnumerable()
+        {
+            string jsonConfig1 = """
+                {
+                  "source": {
+                    "name": "DemoService",
+                    "addresses": [ "127.0.0.1" ]
+                  }
+                }
+                """;
+
+            var configuration = new ConfigurationBuilder()
+                        .AddJsonStream(new MemoryStream(Encoding.UTF8.GetBytes(jsonConfig1)))
+                        .Build();
+
+            ContainingIEnumerable? result = configuration.Get<ContainingIEnumerable>();
+
+            Assert.NotNull(result);
+            Assert.Equal("DemoService", result.Source.Name);
+            Assert.Equal(1, result.Source.Addresses.Count());
+            Assert.Equal("127.0.0.1", result.Source.Addresses.First());
+        }
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -413,8 +413,9 @@ void EmitBindImplForMember(MemberSpec member)`
`413`	`413`	`if (member is ParameterSpec parameter && parameter.ErrorOnFailedBinding)`
`414`	`414`	`{`
`415`	`415`	`// Add exception logic for parameter ctors; must be present in configuration object.`
`416`		- // In case of Arrays, we emit extra block to handle empty arrays. The throw block will not be `else` case at that time.
`417`		`- EmitThrowBlock(condition: _typeIndex.GetEffectiveTypeSpec(member.TypeRef) is ArraySpec ? $"if ({member.Name} is null)" : "else");`
	`416`	+ // In case of Arrays and IEnumerable<T>, we emit extra block to handle collection. The throw block will not be `else` case at that time.
	`417`	`+ TypeSpec typeSpec = _typeIndex.GetEffectiveTypeSpec(member.TypeRef);`
	`418`	`+ EmitThrowBlock(condition: typeSpec is ArraySpec \|\| typeSpec.IsExactIEnumerableOfT ? $"if ({member.Name} is null)" : "else");`
`418`	`419`	`}`
`419`	`420`
`420`	`421`	`_writer.WriteLine();`
Original file line number	Diff line number	Diff line change
`@@ -1184,5 +1184,11 @@ public class MyOptionsWithNullableEnumerable`
`1184`	`1184`	`public IEnumerable<int>? IEnumerableProperty { get; set; }`
`1185`	`1185`	`public string[] StringArray { get; set; }`
`1186`	`1186`	`}`
	`1187`	`+`
	`1188`	`+ internal sealed record ContainingIEnumerable`
	`1189`	`+ {`
	`1190`	`+ public NestedWithIEnumerable? Source { get; set; }`
	`1191`	`+ }`
	`1192`	`+ internal sealed record NestedWithIEnumerable(string Name, IEnumerable<string> Addresses);`
`1187`	`1193`	`}`
`1188`	`1194`	`}`