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/main/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessor.java

@@ -26,6 +26,7 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.Stack;
 
 import javax.annotation.processing.AbstractProcessor;
 import javax.annotation.processing.ProcessingEnvironment;
@@ -258,8 +259,10 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 		Map<String, Object> fieldValues = members.getFieldValues();
 		processSimpleTypes(prefix, element, source, members, fieldValues);
 		processSimpleLombokTypes(prefix, element, source, members, fieldValues);
-		processNestedTypes(prefix, element, source, members);
-		processNestedLombokTypes(prefix, element, source, members);
+		Stack<TypeElement> seen = new Stack<>();
+		seen.push(element);
+		processNestedTypes(prefix, element, source, members, seen);
+		processNestedLombokTypes(prefix, element, source, members, seen);
 	}
 
 	private void processSimpleTypes(String prefix, TypeElement element, ExecutableElement source,
@@ -324,19 +327,19 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 	}
 
 	private void processNestedTypes(String prefix, TypeElement element, ExecutableElement source,
-			TypeElementMembers members) {
+			TypeElementMembers members, Stack<TypeElement> seen) {
 		members.getPublicGetters().forEach((name, getter) -> {
 			VariableElement field = members.getFields().get(name);
-			processNestedType(prefix, element, source, name, getter, field, getter.getReturnType());
+			processNestedType(prefix, element, source, name, getter, field, getter.getReturnType(), seen);
 		});
 	}
 
 	private void processNestedLombokTypes(String prefix, TypeElement element, ExecutableElement source,
-			TypeElementMembers members) {
+			TypeElementMembers members, Stack<TypeElement> seen) {
 		members.getFields().forEach((name, field) -> {
 			if (isLombokField(field, element)) {
 				ExecutableElement getter = members.getPublicGetter(name, field.asType());
-				processNestedType(prefix, element, source, name, getter, field, field.asType());
+				processNestedType(prefix, element, source, name, getter, field, field.asType(), seen);
 			}
 		});
 	}
@@ -378,7 +381,7 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 	}
 
 	private void processNestedType(String prefix, TypeElement element, ExecutableElement source, String name,
-			ExecutableElement getter, VariableElement field, TypeMirror returnType) {
+			ExecutableElement getter, VariableElement field, TypeMirror returnType, Stack<TypeElement> seen) {
 		Element returnElement = this.processingEnv.getTypeUtils().asElement(returnType);
 		boolean isNested = isNested(returnElement, field, element);
 		AnnotationMirror annotation = getAnnotation(getter, configurationPropertiesAnnotation());
@@ -387,7 +390,12 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 			this.metadataCollector
 					.add(ItemMetadata.newGroup(nestedPrefix, this.typeUtils.getQualifiedName(returnElement),
 							this.typeUtils.getQualifiedName(element), (getter != null) ? getter.toString() : null));
-			processTypeElement(nestedPrefix, (TypeElement) returnElement, source);
+			TypeElement nestedElement = (TypeElement) returnElement;
+			if (!seen.contains(nestedElement)) {
+				seen.push(nestedElement);
+				processTypeElement(nestedPrefix, nestedElement, source);
+				seen.pop();
+			}
 		}
 	}
 

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;
+	}
+
+}