Clean line breaks in configuration metadata descriptions.

Closes gh-13601

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

@@ -142,6 +142,7 @@ class TypeUtils {
 		String javadoc = (element != null
 				? this.env.getElementUtils().getDocComment(element) : null);
 		if (javadoc != null) {
+			javadoc = javadoc.replaceAll("\\n", "");
 			javadoc = javadoc.trim();
 		}
 		return ("".equals(javadoc) ? null : javadoc);

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

@@ -55,6 +55,7 @@ import org.springframework.boot.configurationsample.method.MethodAndClassConfig;
 import org.springframework.boot.configurationsample.method.SimpleMethodConfig;
 import org.springframework.boot.configurationsample.simple.ClassWithNestedProperties;
 import org.springframework.boot.configurationsample.simple.DeprecatedSingleProperty;
+import org.springframework.boot.configurationsample.simple.DescriptionProperties;
 import org.springframework.boot.configurationsample.simple.HierarchicalProperties;
 import org.springframework.boot.configurationsample.simple.NotAnnotated;
 import org.springframework.boot.configurationsample.simple.SimpleArrayProperties;
@@ -192,6 +193,20 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 				.fromSource(HierarchicalProperties.class));
 	}
 
+	@Test
+	public void descriptionProperties() {
+		ConfigurationMetadata metadata = compile(DescriptionProperties.class);
+		assertThat(metadata).has(Metadata.withGroup("description")
+				.fromSource(DescriptionProperties.class));
+		assertThat(metadata).has(Metadata.withProperty("description.simple", String.class)
+				.fromSource(DescriptionProperties.class)
+				.withDescription("A simple description."));
+		assertThat(metadata).has(Metadata
+				.withProperty("description.multi-line", String.class)
+				.fromSource(DescriptionProperties.class).withDescription(
+						"This is a lengthy description that spans across multiple lines to showcase that the carriage return is cleaned automatically."));
+	}
+
 	@Test
 	@SuppressWarnings("deprecation")
 	public void deprecatedProperties() throws Exception {

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/simple/DescriptionProperties.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2012-2018 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.simple;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+/**
+ * Configuration properties with various description styles.
+ *
+ * @author Stephane Nicoll
+ */
+@ConfigurationProperties("description")
+public class DescriptionProperties {
+
+	/**
+	 * A simple description.
+	 */
+	private String simple;
+
+	/**
+	 * This is a lengthy description that spans across multiple lines to showcase that the
+	 * carriage return is cleaned automatically.
+	 */
+	private String multiLine;
+
+	public String getSimple() {
+		return this.simple;
+	}
+
+	public void setSimple(String simple) {
+		this.simple = simple;
+	}
+
+	public String getMultiLine() {
+		return this.multiLine;
+	}
+
+	public void setMultiLine(String multiLine) {
+		this.multiLine = multiLine;
+	}
+
+}