From 91c1fc3d97dfca0170752eaddca0d8d956905f41 Mon Sep 17 00:00:00 2001
From: Madhura Bhave <mbhave@pivotal.io>
Date: Mon, 25 Mar 2019 15:49:37 -0700
Subject: [PATCH] Ignore unbound collection properties if collection bound

As of Spring Boot 2.0, if Collection properties are specified in
multiple property sources, only the elements from the property source
with the highest precedence are used for binding. This caused an
`UnboundConfigurationPropertiesException` if the size of the collection
from the higher order property source was smaller and `ignoreUnknownFields`
was set to true.

This commit ignores unbound collection properties if the
collection was properly bound.

Fixes gh-16290
---
 .../handler/NoUnboundElementsBindHandler.java | 18 +++++++-
 .../NoUnboundElementsBindHandlerTests.java    | 43 +++++++++++++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandler.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandler.java
index 4f1ab5e123b..6f175a84658 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandler.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandler.java
@@ -106,7 +106,23 @@ public class NoUnboundElementsBindHandler extends AbstractBindHandler {
 
 	private boolean isUnbound(ConfigurationPropertyName name,
 			ConfigurationPropertyName candidate) {
-		return name.isAncestorOf(candidate) && !this.boundNames.contains(candidate);
+		if (name.isAncestorOf(candidate)) {
+			if (!this.boundNames.contains(candidate)
+					&& !isOverriddenCollectionElement(candidate)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	private boolean isOverriddenCollectionElement(ConfigurationPropertyName candidate) {
+		int length = candidate.getNumberOfElements();
+		if (candidate.isNumericIndex(length - 1)) {
+			ConfigurationPropertyName propertyName = candidate
+					.chop(candidate.getNumberOfElements() - 1);
+			return this.boundNames.contains(propertyName);
+		}
+		return false;
 	}
 
 }
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandlerTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandlerTests.java
index 93bf00bf06f..2d71ff56215 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandlerTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/handler/NoUnboundElementsBindHandlerTests.java
@@ -108,6 +108,35 @@ public class NoUnboundElementsBindHandlerTests {
 		assertThat(bound.getFoo()).isEqualTo("bar");
 	}
 
+	@Test
+	public void bindWhenUsingNoUnboundElementsHandlerShouldBindIfUnboundCollectionProperties() {
+		MockConfigurationPropertySource source1 = new MockConfigurationPropertySource();
+		source1.put("example.foo[0]", "bar");
+		MockConfigurationPropertySource source2 = new MockConfigurationPropertySource();
+		source2.put("example.foo[0]", "bar");
+		source2.put("example.foo[1]", "baz");
+		this.sources.add(source1);
+		this.sources.add(source2);
+		this.binder = new Binder(this.sources);
+		NoUnboundElementsBindHandler handler = new NoUnboundElementsBindHandler();
+		ExampleWithList bound = this.binder
+				.bind("example", Bindable.of(ExampleWithList.class), handler).get();
+		assertThat(bound.getFoo()).containsExactly("bar");
+	}
+
+	@Test
+	public void bindWhenUsingNoUnboundElementsHandlerAndUnboundListElementsShouldThrowException() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("example.foo[0]", "bar");
+		this.sources.add(source);
+		this.binder = new Binder(this.sources);
+		assertThatExceptionOfType(BindException.class)
+				.isThrownBy(() -> this.binder.bind("example", Bindable.of(Example.class),
+						new NoUnboundElementsBindHandler()))
+				.satisfies((ex) -> assertThat(ex.getCause().getMessage())
+						.contains("The elements [example.foo[0]] were left unbound"));
+	}
+
 	public static class Example {
 
 		private String foo;
@@ -122,4 +151,18 @@ public class NoUnboundElementsBindHandlerTests {
 
 	}
 
+	public static class ExampleWithList {
+
+		private List<String> foo;
+
+		public List<String> getFoo() {
+			return this.foo;
+		}
+
+		public void setFoo(List<String> foo) {
+			this.foo = foo;
+		}
+
+	}
+
 }