Polish "Add support for initializing nested object when nothing bound"

This commit harmonizes the change made to @DefaultValue to the
annotation processor. If such annotation is added to a scalar value with
no value at all, no default value is produced.

Closes gh-18917

Author: snicoll

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -19,6 +19,7 @@
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
 import org.springframework.boot.configurationprocessor.metadata.Metadata;
 import org.springframework.boot.configurationsample.recursive.RecursiveProperties;
 import org.springframework.boot.configurationsample.simple.ClassWithNestedProperties;
@@ -39,6 +40,7 @@
 import org.springframework.boot.configurationsample.specific.BuilderPojo;
 import org.springframework.boot.configurationsample.specific.DeprecatedUnrelatedMethodPojo;
 import org.springframework.boot.configurationsample.specific.DoubleRegistrationProperties;
+import org.springframework.boot.configurationsample.specific.EmptyDefaultValueProperties;
 import org.springframework.boot.configurationsample.specific.ExcludedTypesPojo;
 import org.springframework.boot.configurationsample.specific.InnerClassAnnotatedGetterConfig;
 import org.springframework.boot.configurationsample.specific.InnerClassHierarchicalProperties;
@@ -362,6 +364,15 @@ void constructorParameterPropertyWithInvalidDefaultValueOnCharacter() {
 				.withMessageContaining("Compilation failed");
 	}
 
+	@Test
+	void constructorParameterPropertyWithEmptyDefaultValueOnProperty() {
+		ConfigurationMetadata metadata = compile(EmptyDefaultValueProperties.class);
+		assertThat(metadata).has(Metadata.withProperty("test.name"));
+		ItemMetadata nameMetadata = metadata.getItems().stream().filter((item) -> item.getName().equals("test.name"))
+				.findFirst().get();
+		assertThat(nameMetadata.getDefaultValue()).isNull();
+	}
+
 	@Test
 	void recursivePropertiesDoNotCauseAStackOverflow() {
 		compile(RecursiveProperties.class);

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/DeducedImmutablePropertiesMetadataGenerationTests.java

@@ -19,6 +19,7 @@
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
 import org.springframework.boot.configurationprocessor.metadata.Metadata;
 import org.springframework.boot.configurationsample.immutable.DeducedImmutableClassProperties;
 
@@ -28,14 +29,21 @@
  * Metadata generation tests for immutable properties deduced because they're nested.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 class DeducedImmutablePropertiesMetadataGenerationTests extends AbstractMetadataGenerationTests {
 
 	@Test
 	void immutableSimpleProperties() {
 		ConfigurationMetadata metadata = compile(DeducedImmutableClassProperties.class);
 		assertThat(metadata).has(Metadata.withGroup("test").fromSource(DeducedImmutableClassProperties.class));
-		assertThat(metadata).has(Metadata.withProperty("test.nested.name", String.class));
+		assertThat(metadata).has(Metadata.withGroup("test.nested", DeducedImmutableClassProperties.Nested.class)
+				.fromSource(DeducedImmutableClassProperties.class));
+		assertThat(metadata).has(Metadata.withProperty("test.nested.name", String.class)
+				.fromSource(DeducedImmutableClassProperties.Nested.class));
+		ItemMetadata nestedMetadata = metadata.getItems().stream()
+				.filter((item) -> item.getName().equals("test.nested")).findFirst().get();
+		assertThat(nestedMetadata.getDefaultValue()).isNull();
 	}
 
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/DefaultValue.java

@@ -33,6 +33,6 @@
 @Documented
 public @interface DefaultValue {
 
-	String[] value();
+	String[] value() default {};
 
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/immutable/DeducedImmutableClassProperties.java

@@ -18,6 +18,7 @@
 
 import org.springframework.boot.configurationsample.ConfigurationProperties;
 import org.springframework.boot.configurationsample.ConstructorBinding;
+import org.springframework.boot.configurationsample.DefaultValue;
 
 /**
  * Inner properties, in immutable format.
@@ -30,7 +31,7 @@ public class DeducedImmutableClassProperties {
 
 	private final Nested nested;
 
-	public DeducedImmutableClassProperties(Nested nested) {
+	public DeducedImmutableClassProperties(@DefaultValue Nested nested) {
 		this.nested = nested;
 	}
 

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/specific/EmptyDefaultValueProperties.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2012-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationsample.specific;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+import org.springframework.boot.configurationsample.ConstructorBinding;
+import org.springframework.boot.configurationsample.DefaultValue;
+
+/**
+ * Demonstrates that an empty default value on a property leads to no default value.
+ *
+ * @author Stephane Nicoll
+ */
+@ConfigurationProperties("test")
+public class EmptyDefaultValueProperties {
+
+	private final String name;
+
+	@ConstructorBinding
+	public EmptyDefaultValueProperties(@DefaultValue String name) {
+		this.name = name;
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+}