Prevent recursive config props from causing a stack overflow

Previously, when the configuration properties annotation processor
encountered a property that was the same as an outer type that had
already been processed, it would fail with a stack overflow error.

This commit introduces the use of a stack to track the types that
have been processed. Types that have been seen before are skipped,
thereby preventing a failure from occurring. We do not fail upon
encountering a recursive type to allow metadata generation to
complete. At runtime, the recursive property will not cause a problem
if it is not bound.

Fixes gh-18365

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

@@ -68,6 +68,7 @@ import org.springframework.boot.configurationsample.method.EmptyTypeMethodConfig
 import org.springframework.boot.configurationsample.method.InvalidMethodConfig;
 import org.springframework.boot.configurationsample.method.MethodAndClassConfig;
 import org.springframework.boot.configurationsample.method.SimpleMethodConfig;
+import org.springframework.boot.configurationsample.recursive.RecursiveProperties;
 import org.springframework.boot.configurationsample.simple.ClassWithNestedProperties;
 import org.springframework.boot.configurationsample.simple.DeprecatedFieldSingleProperty;
 import org.springframework.boot.configurationsample.simple.DeprecatedSingleProperty;
@@ -970,6 +971,11 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 				.has(Metadata.withProperty("bar.counter").withDefaultValue(0).fromSource(RenamedBarProperties.class));
 	}
 
+	@Test
+	public void recursivePropertiesDoNotCauseAStackOverflow() {
+		compile(RecursiveProperties.class);
+	}
+
 	private void assertSimpleLombokProperties(ConfigurationMetadata metadata, Class<?> source, String prefix) {
 		assertThat(metadata).has(Metadata.withGroup(prefix).fromSource(source));
 		assertThat(metadata).doesNotHave(Metadata.withProperty(prefix + ".id"));

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

@@ -0,0 +1,34 @@
+/*
+ * 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
+ *
+ *      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.recursive;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+@ConfigurationProperties("prefix")
+public class RecursiveProperties {
+
+	private RecursiveProperties recursive;
+
+	public RecursiveProperties getRecursive() {
+		return this.recursive;
+	}
+
+	public void setRecursive(RecursiveProperties recursive) {
+		this.recursive = recursive;
+	}
+
+}