Binding to collection of custom objects should not fail with unbound error

Fixes gh-20134

Author: mbhave

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

@@ -43,6 +43,8 @@ public class NoUnboundElementsBindHandler extends AbstractBindHandler {
 
 	private final Set<ConfigurationPropertyName> boundNames = new HashSet<>();
 
+	private final Set<ConfigurationPropertyName> attemptedNames = new HashSet<>();
+
 	private final Function<ConfigurationPropertySource, Boolean> filter;
 
 	NoUnboundElementsBindHandler() {
@@ -58,6 +60,12 @@ public NoUnboundElementsBindHandler(BindHandler parent, Function<ConfigurationPr
 		this.filter = filter;
 	}
 
+	@Override
+	public <T> Bindable<T> onStart(ConfigurationPropertyName name, Bindable<T> target, BindContext context) {
+		this.attemptedNames.add(name);
+		return super.onStart(name, target, context);
+	}
+
 	@Override
 	public Object onSuccess(ConfigurationPropertyName name, Bindable<?> target, BindContext context, Object result) {
 		this.boundNames.add(name);
@@ -108,11 +116,54 @@ private boolean isUnbound(ConfigurationPropertyName name, ConfigurationPropertyN
 
 	private boolean isOverriddenCollectionElement(ConfigurationPropertyName candidate) {
 		int lastIndex = candidate.getNumberOfElements() - 1;
-		if (candidate.isNumericIndex(lastIndex)) {
+		if (candidate.isLastElementIndexed()) {
 			ConfigurationPropertyName propertyName = candidate.chop(lastIndex);
 			return this.boundNames.contains(propertyName);
 		}
+		Indexed indexed = getIndexed(candidate);
+		if (indexed != null) {
+			String zeroethProperty = indexed.getName() + "[0]";
+			if (this.boundNames.contains(ConfigurationPropertyName.of(zeroethProperty))) {
+				String nestedZeroethProperty = zeroethProperty + "." + indexed.getNestedPropertyName();
+				return isCandidateValidPropertyName(nestedZeroethProperty);
+			}
+		}
 		return false;
 	}
 
+	private boolean isCandidateValidPropertyName(String nestedZeroethProperty) {
+		return this.attemptedNames.contains(ConfigurationPropertyName.of(nestedZeroethProperty));
+	}
+
+	private Indexed getIndexed(ConfigurationPropertyName candidate) {
+		for (int i = 0; i < candidate.getNumberOfElements(); i++) {
+			if (candidate.isNumericIndex(i)) {
+				return new Indexed(candidate.chop(i).toString(),
+						candidate.getElement(i + 1, ConfigurationPropertyName.Form.UNIFORM));
+			}
+		}
+		return null;
+	}
+
+	private static final class Indexed {
+
+		private final String name;
+
+		private final String nestedPropertyName;
+
+		private Indexed(String name, String nestedPropertyName) {
+			this.name = name;
+			this.nestedPropertyName = nestedPropertyName;
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+		public String getNestedPropertyName() {
+			return this.nestedPropertyName;
+		}
+
+	}
+
 }

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

@@ -131,6 +131,42 @@ public void bindWhenUsingNoUnboundElementsHandlerAndUnboundListElementsShouldThr
 						.contains("The elements [example.foo[0]] were left unbound"));
 	}
 
+	@Test
+	public void bindWhenUsingNoUnboundElementsHandlerShouldBindIfUnboundNestedCollectionProperties() {
+		MockConfigurationPropertySource source1 = new MockConfigurationPropertySource();
+		source1.put("example.nested[0].string-value", "bar");
+		MockConfigurationPropertySource source2 = new MockConfigurationPropertySource();
+		source2.put("example.nested[0].string-value", "bar");
+		source2.put("example.nested[0].int-value", "2");
+		source2.put("example.nested[1].string-value", "baz");
+		source2.put("example.nested[1].other-nested.baz", "baz");
+		this.sources.add(source1);
+		this.sources.add(source2);
+		this.binder = new Binder(this.sources);
+		NoUnboundElementsBindHandler handler = new NoUnboundElementsBindHandler();
+		ExampleWithNestedList bound = this.binder.bind("example", Bindable.of(ExampleWithNestedList.class), handler)
+				.get();
+		assertThat(bound.getNested().get(0).getStringValue()).isEqualTo("bar");
+	}
+
+	@Test
+	public void bindWhenUsingNoUnboundElementsHandlerAndUnboundCollectionElementsWithInvalidPropertyShouldThrowException() {
+		MockConfigurationPropertySource source1 = new MockConfigurationPropertySource();
+		source1.put("example.nested[0].string-value", "bar");
+		MockConfigurationPropertySource source2 = new MockConfigurationPropertySource();
+		source2.put("example.nested[0].string-value", "bar");
+		source2.put("example.nested[1].int-value", "1");
+		source2.put("example.nested[1].invalid", "baz");
+		this.sources.add(source1);
+		this.sources.add(source2);
+		this.binder = new Binder(this.sources);
+		assertThatExceptionOfType(BindException.class)
+				.isThrownBy(() -> this.binder.bind("example", Bindable.of(ExampleWithNestedList.class),
+						new NoUnboundElementsBindHandler()))
+				.satisfies((ex) -> assertThat(ex.getCause().getMessage())
+						.contains("The elements [example.nested[1].invalid] were left unbound"));
+	}
+
 	public static class Example {
 
 		private String foo;
@@ -159,4 +195,66 @@ public void setFoo(List<String> foo) {
 
 	}
 
+	public static class ExampleWithNestedList {
+
+		private List<Nested> nested;
+
+		public List<Nested> getNested() {
+			return this.nested;
+		}
+
+		public void setNested(List<Nested> nested) {
+			this.nested = nested;
+		}
+
+	}
+
+	static class Nested {
+
+		private String stringValue;
+
+		private Integer intValue;
+
+		private OtherNested otherNested;
+
+		public String getStringValue() {
+			return this.stringValue;
+		}
+
+		public void setStringValue(String value) {
+			this.stringValue = value;
+		}
+
+		public Integer getIntValue() {
+			return this.intValue;
+		}
+
+		public void setIntValue(Integer intValue) {
+			this.intValue = intValue;
+		}
+
+		public OtherNested getOtherNested() {
+			return this.otherNested;
+		}
+
+		public void setOtherNested(OtherNested otherNested) {
+			this.otherNested = otherNested;
+		}
+
+	}
+
+	static class OtherNested {
+
+		private String baz;
+
+		public String getBaz() {
+			return this.baz;
+		}
+
+		public void setBaz(String baz) {
+			this.baz = baz;
+		}
+
+	}
+
 }