Fix detection of Autowired constructor with Kotlin

Previously, the import selector wrongly assumed that we should not
use constructor injection with Kotlin. Rather than looking up for the
primary constructor, we retrieve available constructors on the Java
counter-part.

This commit applies the same logic as in the constructor parameter
binder and checks for the primary constructor for Kotlin types.

See gh-8762

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

@@ -17,11 +17,13 @@
 package org.springframework.boot.context.properties;
 
 import java.lang.reflect.Constructor;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
 
+import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -30,6 +32,7 @@ import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.GenericBeanDefinition;
 import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
 import org.springframework.context.annotation.ImportSelector;
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.util.Assert;
@@ -52,6 +55,8 @@ import org.springframework.util.StringUtils;
  */
 class EnableConfigurationPropertiesImportSelector implements ImportSelector {
 
+	private static boolean KOTLIN_PRESENT = KotlinDetector.isKotlinPresent();
+
 	private static final String[] IMPORTS = {
 			ConfigurationPropertiesBeanRegistrar.class.getName(),
 			ConfigurationPropertiesBindingPostProcessorRegistrar.class.getName() };
@@ -145,13 +150,29 @@ class EnableConfigurationPropertiesImportSelector implements ImportSelector {
 		}
 
 		private boolean canBindAtCreationTime(Class<?> type) {
-			Constructor<?>[] constructors = type.getDeclaredConstructors();
-			boolean autowiredPresent = Arrays.stream(constructors).anyMatch(
+			List<Constructor<?>> constructors = determineConstructors(type);
+			boolean autowiredPresent = constructors.stream().anyMatch(
 					(c) -> AnnotationUtils.findAnnotation(c, Autowired.class) != null);
 			if (autowiredPresent) {
 				return false;
 			}
-			return (constructors.length == 1 && constructors[0].getParameterCount() > 0);
+			return (constructors.size() == 1
+					&& constructors.get(0).getParameterCount() > 0);
+		}
+
+		private List<Constructor<?>> determineConstructors(Class<?> type) {
+			List<Constructor<?>> constructors = new ArrayList<>();
+			if (KOTLIN_PRESENT && KotlinDetector.isKotlinType(type)) {
+				Constructor<?> primaryConstructor = BeanUtils
+						.findPrimaryConstructor(type);
+				if (primaryConstructor != null) {
+					constructors.add(primaryConstructor);
+				}
+			}
+			else {
+				constructors.addAll(Arrays.asList(type.getDeclaredConstructors()));
+			}
+			return constructors;
 		}
 
 	}

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

@@ -0,0 +1,87 @@
+package org.springframework.boot.context.properties
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.beans.factory.support.DefaultListableBeanFactory
+import org.springframework.beans.factory.support.GenericBeanDefinition
+import org.springframework.core.type.AnnotationMetadata
+import org.springframework.core.type.classreading.SimpleMetadataReaderFactory
+
+/**
+ * Tests for `EnableConfigurationPropertiesImportSelector`.
+ *
+ * @author Stephane Nicoll
+ */
+@Suppress("unused")
+class KotlinEnableConfigurationPropertiesImportSelectorTests {
+
+	private val registrar = EnableConfigurationPropertiesImportSelector.ConfigurationPropertiesBeanRegistrar()
+
+	private val beanFactory = DefaultListableBeanFactory()
+
+
+	@Test
+	fun `type with default constructor should register generic bean definition`() {
+		this.registrar.registerBeanDefinitions(
+				getAnnotationMetadata(TestConfiguration::class.java), this.beanFactory)
+		val beanDefinition = this.beanFactory.getBeanDefinition(
+				"foo-org.springframework.boot.context.properties.KotlinEnableConfigurationPropertiesImportSelectorTests\$FooProperties")
+		assertThat(beanDefinition).isExactlyInstanceOf(GenericBeanDefinition::class.java)
+	}
+
+	@Test
+	fun `type with autowired on constructor should register generic bean definition`() {
+		this.registrar.registerBeanDefinitions(
+				getAnnotationMetadata(TestConfiguration::class.java), this.beanFactory)
+		val beanDefinition = this.beanFactory.getBeanDefinition(
+				"bar-org.springframework.boot.context.properties.KotlinEnableConfigurationPropertiesImportSelectorTests\$BarProperties")
+		assertThat(beanDefinition).isExactlyInstanceOf(GenericBeanDefinition::class.java)
+	}
+
+	@Test
+	fun `type with primary constructor and no autowired should register configuration properties bean definition`() {
+		this.registrar.registerBeanDefinitions(
+				getAnnotationMetadata(TestConfiguration::class.java), this.beanFactory)
+		val beanDefinition = this.beanFactory.getBeanDefinition(
+				"baz-org.springframework.boot.context.properties.KotlinEnableConfigurationPropertiesImportSelectorTests\$BazProperties")
+		assertThat(beanDefinition).isExactlyInstanceOf(ConfigurationPropertiesBeanDefinition::class.java)
+	}
+
+	@Test
+	fun `type with no primary constructor should register generic bean definition`() {
+		this.registrar.registerBeanDefinitions(
+				getAnnotationMetadata(TestConfiguration::class.java), this.beanFactory)
+		val beanDefinition = this.beanFactory.getBeanDefinition(
+				"bing-org.springframework.boot.context.properties.KotlinEnableConfigurationPropertiesImportSelectorTests\$BingProperties")
+		assertThat(beanDefinition).isExactlyInstanceOf(GenericBeanDefinition::class.java)
+	}
+
+	private fun getAnnotationMetadata(source: Class<*>): AnnotationMetadata {
+		return SimpleMetadataReaderFactory().getMetadataReader(source.name)
+				.annotationMetadata
+	}
+
+
+	@EnableConfigurationProperties(FooProperties::class, BarProperties::class, BazProperties::class, BingProperties::class)
+	class TestConfiguration
+
+	@ConfigurationProperties(prefix = "foo")
+	class FooProperties
+
+	@ConfigurationProperties(prefix = "bar")
+	class BarProperties @Autowired constructor(val foo: String)
+
+	@ConfigurationProperties(prefix = "baz")
+	class BazProperties(val name: String?, val counter: Int = 42)
+
+	@ConfigurationProperties(prefix = "bing")
+	class BingProperties {
+
+		constructor()
+
+		constructor(@Suppress("UNUSED_PARAMETER") foo: String)
+
+	}
+
+}