Add ability to ignore configuration properties

Properties which should be ignored can be specified in the
additional-spring-configuration-metadata.json file. The ignored
properties section is copied into the final
spring-configuration-metadata.json file, and the ignored properties are
removed from the properties element in the final file.

Closes gh-2421

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -22,6 +22,7 @@ import java.time.temporal.ChronoUnit;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.ItemIgnore;
 import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
 import org.springframework.boot.configurationprocessor.metadata.Metadata;
 import org.springframework.boot.configurationsample.deprecation.Dbcp2Configuration;
@@ -38,6 +39,7 @@ import org.springframework.boot.configurationsample.simple.DescriptionProperties
 import org.springframework.boot.configurationsample.simple.HierarchicalProperties;
 import org.springframework.boot.configurationsample.simple.HierarchicalPropertiesGrandparent;
 import org.springframework.boot.configurationsample.simple.HierarchicalPropertiesParent;
+import org.springframework.boot.configurationsample.simple.IgnoredProperties;
 import org.springframework.boot.configurationsample.simple.InnerClassWithPrivateConstructor;
 import org.springframework.boot.configurationsample.simple.NotAnnotated;
 import org.springframework.boot.configurationsample.simple.SimpleArrayProperties;
@@ -570,4 +572,24 @@ class ConfigurationMetadataAnnotationProcessorTests extends AbstractMetadataGene
 			.withDescription("last description in Javadoc"));
 	}
 
+	@Test
+	void shouldIgnoreProperties() {
+		String additionalMetadata = """
+				{
+					"ignored": {
+						"properties": [
+							{
+								"name": "ignored.prop3"
+							}
+						]
+					}
+				}
+				""";
+		ConfigurationMetadata metadata = compile(additionalMetadata, IgnoredProperties.class);
+		assertThat(metadata).has(Metadata.withProperty("ignored.prop1", String.class));
+		assertThat(metadata).has(Metadata.withProperty("ignored.prop2", String.class));
+		assertThat(metadata).doesNotHave(Metadata.withProperty("ignored.prop3", String.class));
+		assertThat(metadata.getIgnored()).containsExactly(ItemIgnore.forProperty("ignored.prop3"));
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -34,6 +34,7 @@ import static org.assertj.core.api.Assertions.assertThatException;
  *
  * @author Phillip Webb
  * @author Stephane Nicoll
+ * @author Moritz Halbritter
  */
 class JsonMarshallerTests {
 
@@ -174,14 +175,36 @@ class JsonMarshallerTests {
 				"\"java.lang.Boolean\"", "\"com.example.bravo.aaa\"", "\"java.lang.Integer\"", "\"com.example.Bar");
 	}
 
+	@Test
+	void shouldReadIgnoredProperties() throws Exception {
+		String json = """
+				{
+					"ignored": {
+						"properties": [
+							{
+								"name": "prop1"
+							},
+							{
+								"name": "prop2"
+							}
+						]
+					}
+				}
+				""";
+		ConfigurationMetadata metadata = read(json);
+		assertThat(metadata.getIgnored()).containsExactly(ItemIgnore.forProperty("prop1"),
+				ItemIgnore.forProperty("prop2"));
+	}
+
 	@Test
 	void shouldCheckRootFields() {
 		String json = """
 				{
-					"groups": [], "properties": [], "hints": [], "dummy": []
+					"groups": [], "properties": [], "hints": [], "ignored": {}, "dummy": []
 				}""";
 		assertThatException().isThrownBy(() -> read(json))
-			.withMessage("Expected only keys [groups, hints, properties], but found additional keys [dummy]. Path: .");
+			.withMessage(
+					"Expected only keys [groups, hints, ignored, properties], but found additional keys [dummy]. Path: .");
 	}
 
 	@Test
@@ -324,9 +347,41 @@ class JsonMarshallerTests {
 					"Expected only keys [name, parameters], but found additional keys [dummy]. Path: .hints.[0].providers.[0]");
 	}
 
-	private void read(String json) throws Exception {
+	@Test
+	void shouldCheckIgnoreFields() {
+		String json = """
+				{
+					"ignored": {
+						"properties": [],
+						"dummy": {}
+					}
+				}
+				""";
+		assertThatException().isThrownBy(() -> read(json))
+			.withMessage("Expected only keys [properties], but found additional keys [dummy]. Path: .ignored");
+	}
+
+	@Test
+	void shouldCheckIgnorePropertiesFields() {
+		String json = """
+				{
+					"ignored": {
+						"properties": [
+							{
+								"name": "prop1",
+								"dummy": true
+							}
+						]
+					}
+				}
+				""";
+		assertThatException().isThrownBy(() -> read(json))
+			.withMessage("Expected only keys [name], but found additional keys [dummy]. Path: .ignored.properties.[0]");
+	}
+
+	private ConfigurationMetadata read(String json) throws Exception {
 		JsonMarshaller marshaller = new JsonMarshaller();
-		marshaller.read(new ByteArrayInputStream(json.getBytes(StandardCharsets.UTF_8)));
+		return marshaller.read(new ByteArrayInputStream(json.getBytes(StandardCharsets.UTF_8)));
 	}
 
 }

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

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2012-2025 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.simple;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+/**
+ * Configuration properties where some of them are being ignored.
+ *
+ * @author Moritz Halbritter
+ */
+@ConfigurationProperties("ignored")
+public class IgnoredProperties {
+
+	private String prop1;
+
+	private String prop2;
+
+	private String prop3;
+
+	public String getProp1() {
+		return this.prop1;
+	}
+
+	public void setProp1(String prop1) {
+		this.prop1 = prop1;
+	}
+
+	public String getProp2() {
+		return this.prop2;
+	}
+
+	public void setProp2(String prop2) {
+		this.prop2 = prop2;
+	}
+
+	public String getProp3() {
+		return this.prop3;
+	}
+
+	public void setProp3(String prop3) {
+		this.prop3 = prop3;
+	}
+
+}