Detect builder-style setter

Previously, a setter method that was returning the current instance was
not identified as a "setter" by the configuration processor. As a result,
builder-style APIs were not covered by the configuration metadata.

If a setter returns either void or the current class, it is now
recognized as a valid setter.

Fixes gh-1854

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/TypeElementMembers.java

@@ -91,7 +91,12 @@ class TypeElementMembers {
 	private boolean isSetter(ExecutableElement method) {
 		final String name = method.getSimpleName().toString();
 		return name.startsWith("set") && method.getParameters().size() == 1
-				&& (TypeKind.VOID == method.getReturnType().getKind());
+				&& (isSetterReturnType(method));
+	}
+
+	private boolean isSetterReturnType(ExecutableElement method) {
+		return (TypeKind.VOID == method.getReturnType().getKind()
+				|| method.getEnclosingElement().asType().equals(method.getReturnType()));
 	}
 
 	private String getAccessorName(String methodName) {

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

@@ -36,6 +36,7 @@ import org.springframework.boot.configurationsample.simple.SimpleCollectionPrope
 import org.springframework.boot.configurationsample.simple.SimplePrefixValueProperties;
 import org.springframework.boot.configurationsample.simple.SimpleProperties;
 import org.springframework.boot.configurationsample.simple.SimpleTypeProperties;
+import org.springframework.boot.configurationsample.specific.BuilderPojo;
 import org.springframework.boot.configurationsample.specific.InnerClassAnnotatedGetterConfig;
 import org.springframework.boot.configurationsample.specific.InnerClassProperties;
 import org.springframework.boot.configurationsample.specific.InnerClassRootConfig;
@@ -251,6 +252,12 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 		assertThat(metadata, not(containsProperty("specific.foo")));
 	}
 
+	@Test
+	public void builderPojo() throws IOException {
+		ConfigurationMetadata metadata = compile(BuilderPojo.class);
+		assertThat(metadata, containsProperty("builder.name"));
+	}
+
 	private ConfigurationMetadata compile(Class<?>... types) throws IOException {
 		TestConfigurationMetadataAnnotationProcessor processor = new TestConfigurationMetadataAnnotationProcessor();
 		new TestCompiler(this.temporaryFolder).getTask(types).call(processor);

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

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2014 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
+ *
+ *      http://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;
+
+/**
+ *
+ * @author Stephane Nicoll
+ */
+@ConfigurationProperties(prefix = "builder")
+public class BuilderPojo {
+
+	private String name;
+
+	public String getName() {
+		return name;
+	}
+
+	public BuilderPojo setName(String name) {
+		this.name = name;
+		return this;
+	}
+}