Use existing value rather than deducing bind method

When there is an existing value, deducing the bind method may
incorrectly result in the use of constructor binding. This
results in a failure in the configuration properties
post-processor as it refuses to bind properties to a bean whose
attributes indicate that constructor binding should have been used.

This commit updates ConfigurationPropertiesBean to avoid tryin to
deduce the bind method and instead use the presence or absence of an
existing value to determine the type of binding that should be used.
Only when there is no existing value is constructor binding
appropriate.

Fixes gh-36175

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBean.java

@@ -216,9 +216,6 @@ public final class ConfigurationPropertiesBean {
 		if (bindTarget.getBindMethod() == null && factoryMethod != null) {
 			bindTarget = bindTarget.withBindMethod(JAVA_BEAN_BIND_METHOD);
 		}
-		if (bindTarget.getBindMethod() == null) {
-			bindTarget = bindTarget.withBindMethod(deduceBindMethod(bindTarget));
-		}
 		if (bindTarget.getBindMethod() != VALUE_OBJECT_BIND_METHOD) {
 			bindTarget = bindTarget.withExistingValue(bean);
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/ConfigurationPropertiesTests.java

@@ -72,6 +72,7 @@ import org.springframework.boot.testsupport.system.OutputCaptureExtension;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.ImportResource;
 import org.springframework.context.annotation.Scope;
 import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
@@ -1152,6 +1153,14 @@ class ConfigurationPropertiesTests {
 		assertThat(bean.getNested().name()).isEqualTo("spring");
 	}
 
+	@Test
+	void loadWhenPotentiallyConstructorBoundPropertiesAreImportedUsesJavaBeanBinding() {
+		load(PotentiallyConstructorBoundPropertiesImporter.class, "test.prop=alpha");
+		PotentiallyConstructorBoundProperties properties = this.context
+			.getBean(PotentiallyConstructorBoundProperties.class);
+		assertThat(properties.getProp()).isEqualTo("alpha");
+	}
+
 	private AnnotationConfigApplicationContext load(Class<?> configuration, String... inlinedProperties) {
 		return load(new Class<?>[] { configuration }, inlinedProperties);
 	}
@@ -3004,4 +3013,34 @@ class ConfigurationPropertiesTests {
 	static record NestedRecord(String name) {
 	}
 
+	@EnableConfigurationProperties
+	@Import(PotentiallyConstructorBoundProperties.class)
+	static class PotentiallyConstructorBoundPropertiesImporter {
+
+		@Bean
+		String notAProperty() {
+			return "notAProperty";
+		}
+
+	}
+
+	@ConfigurationProperties("test")
+	static class PotentiallyConstructorBoundProperties {
+
+		private String prop;
+
+		PotentiallyConstructorBoundProperties(String notAProperty) {
+
+		}
+
+		String getProp() {
+			return this.prop;
+		}
+
+		void setProp(String prop) {
+			this.prop = prop;
+		}
+
+	}
+
 }

spring-boot-project/spring-boot/src/test/kotlin/org/springframework/boot/context/properties/KotlinConfigurationPropertiesTests.kt

@@ -22,6 +22,7 @@ import org.springframework.beans.factory.support.BeanDefinitionRegistry
 import org.springframework.beans.factory.support.RootBeanDefinition
 import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Configuration
+import org.springframework.context.annotation.Import
 import org.springframework.test.context.support.TestPropertySourceUtils
 
 import org.assertj.core.api.Assertions.assertThat
@@ -68,6 +69,14 @@ class KotlinConfigurationPropertiesTests {
 		assertThat(properties.inner.bravo).isEqualTo("two")
 	}
 
+	@Test
+	fun `mutable data class properties can be imported`() {
+		this.context.register(MutableDataClassPropertiesImporter::class.java)
+		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.context, "mutable.prop=alpha");
+		this.context.refresh();
+		assertThat(this.context.getBean(MutableDataClassProperties::class.java).prop).isEqualTo("alpha")
+	}
+
 	@ConfigurationProperties(prefix = "foo")
 	class BingProperties(@Suppress("UNUSED_PARAMETER") bar: String) {
 
@@ -106,4 +115,15 @@ class KotlinConfigurationPropertiesTests {
 
 	}
 
+	@EnableConfigurationProperties
+	@Configuration(proxyBeanMethods = false)
+	@Import(MutableDataClassProperties::class)
+	class MutableDataClassPropertiesImporter {
+	}
+
+	@ConfigurationProperties(prefix = "mutable")
+	data class MutableDataClassProperties(
+		var prop: String = ""
+	)
+
 }