Allow recursive list binding when iterable source

Further refine recursive binding rules so that Lists are supported when
the underlying source is iterable.

Close gh-10702

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/AggregateBinder.java

@@ -19,6 +19,7 @@ package org.springframework.boot.context.properties.bind;
 import java.util.function.Supplier;
 
 import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
+import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
 
 /**
  * Internal strategy used by {@link Binder} to bind aggregates (Maps, Lists, Arrays).
@@ -31,16 +32,17 @@ abstract class AggregateBinder<T> {
 
 	private final BindContext context;
 
-	private final boolean allowRecursiveBinding;
-
-	AggregateBinder(BindContext context, boolean allowRecursiveBinding) {
+	AggregateBinder(BindContext context) {
 		this.context = context;
-		this.allowRecursiveBinding = allowRecursiveBinding;
 	}
 
-	boolean isAllowRecursiveBinding() {
-		return this.allowRecursiveBinding;
-	}
+	/**
+	 * Determine if recursive binding is supported.
+	 * @param source the configuration property source or {@code null} for all sources.
+	 * @return if recursive binding is supported
+	 */
+	protected abstract boolean isAllowRecursiveBinding(
+			ConfigurationPropertySource source);
 
 	/**
 	 * Perform binding for the aggregate.

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/Binder.java

@@ -266,8 +266,10 @@ public class Binder {
 	private <T> Object bindAggregate(ConfigurationPropertyName name, Bindable<T> target,
 			BindHandler handler, Context context, AggregateBinder<?> aggregateBinder) {
 		AggregateElementBinder elementBinder = (itemName, itemTarget, source) -> {
+			boolean allowRecursiveBinding = aggregateBinder
+					.isAllowRecursiveBinding(source);
 			Supplier<?> supplier = () -> bind(itemName, itemTarget, handler, context,
-					aggregateBinder.isAllowRecursiveBinding());
+					allowRecursiveBinding);
 			return context.withSource(source, supplier);
 		};
 		return context.withIncreasedDepth(

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/IndexedElementsBinder.java

@@ -45,7 +45,12 @@ abstract class IndexedElementsBinder<T> extends AggregateBinder<T> {
 	private static final String INDEX_ZERO = "[0]";
 
 	IndexedElementsBinder(BindContext context) {
-		super(context, false);
+		super(context);
+	}
+
+	@Override
+	protected boolean isAllowRecursiveBinding(ConfigurationPropertySource source) {
+		return source == null || source instanceof IterableConfigurationPropertySource;
 	}
 
 	protected final void bindIndexed(ConfigurationPropertyName name, Bindable<?> target,

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/MapBinder.java

@@ -41,7 +41,12 @@ class MapBinder extends AggregateBinder<Map<Object, Object>> {
 			.mapOf(String.class, String.class);
 
 	MapBinder(BindContext context) {
-		super(context, true);
+		super(context);
+	}
+
+	@Override
+	protected boolean isAllowRecursiveBinding(ConfigurationPropertySource source) {
+		return true;
 	}
 
 	@Override

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/CollectionBinderTests.java

@@ -351,6 +351,7 @@ public class CollectionBinderTests {
 		assertThat(result.getItemsSet()).containsExactly("a", "b", "c");
 	}
 
+	@Test
 	public void bindToBeanWithNestedCollectionShouldPopulateCollection()
 			throws Exception {
 		MockConfigurationPropertySource source = new MockConfigurationPropertySource();