Add `include` support to @EnableAutoConfiguration

Update the `@EnableAutoConfiguration` annotation to include an `include`
attribute which can be used to specify specific auto-configuration
classes.

Primarily added to so that tests can selectively auto-configure without
needing to worry about class import order.

Fixes gh-3660

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/EnableAutoConfiguration.java

@@ -75,6 +75,15 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
 		AutoConfigurationPackages.Registrar.class })
 public @interface EnableAutoConfiguration {
 
+	/**
+	 * Include only the specified auto-configuration classes and do not attempt full
+	 * auto-configuration. Using this attribute means that {@code spring.factories} files
+	 * will not be considered. This attribute should not generally be specified in
+	 * production applications, however, it is useful for tests.
+	 * @return the classes to include
+	 */
+	Class<?>[] include() default {};
+
 	/**
 	 * Exclude specific auto-configuration classes such that they will never be applied.
 	 * @return the classes to exclude

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/EnableAutoConfigurationImportSelector.java

@@ -75,14 +75,12 @@ class EnableAutoConfigurationImportSelector implements DeferredImportSelector,
 					+ " annotated with @EnableAutoConfiguration?");
 
 			// Find all possible auto configuration classes, filtering duplicates
-			List<String> factories = new ArrayList<String>(new LinkedHashSet<String>(
-					SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class,
-							this.beanClassLoader)));
+			List<String> factories = getFactories(attributes);
 
 			// Remove those specifically excluded
 			Set<String> excluded = new LinkedHashSet<String>();
-			excluded.addAll(Arrays.asList(attributes.getStringArray("exclude")));
-			excluded.addAll(Arrays.asList(attributes.getStringArray("excludeName")));
+			excluded.addAll(asList(attributes, "exclude"));
+			excluded.addAll(asList(attributes, "excludeName"));
 			excluded.addAll(getExcludeAutoConfigurationsProperty());
 			factories.removeAll(excluded);
 			ConditionEvaluationReport.get(this.beanFactory).recordExclusions(excluded);
@@ -100,6 +98,20 @@ class EnableAutoConfigurationImportSelector implements DeferredImportSelector,
 		}
 	}
 
+	private List<String> getFactories(AnnotationAttributes attributes) {
+		List<String> factories = asList(attributes, "include");
+		if (factories.isEmpty()) {
+			factories = SpringFactoriesLoader.loadFactoryNames(
+					EnableAutoConfiguration.class, this.beanClassLoader);
+		}
+		return new ArrayList<String>(new LinkedHashSet<String>(factories));
+	}
+
+	private List<String> asList(AnnotationAttributes attributes, String name) {
+		String[] value = attributes.getStringArray(name);
+		return Arrays.asList(value == null ? new String[0] : value);
+	}
+
 	private List<String> getExcludeAutoConfigurationsProperty() {
 		RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(this.environment,
 				"spring.autoconfigure.");

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/EnableAutoConfigurationImportSelectorTests.java

@@ -148,6 +148,18 @@ public class EnableAutoConfigurationImportSelectorTests {
 						ThymeleafAutoConfiguration.class.getName()));
 	}
 
+	@Test
+	public void classIncludesAreApplied() throws Exception {
+		given(
+				this.annotationMetadata.getAnnotationAttributes(
+						EnableAutoConfiguration.class.getName(), true)).willReturn(
+				this.annotationAttributes);
+		given(this.annotationAttributes.getStringArray("include")).willReturn(
+				new String[] { FreeMarkerAutoConfiguration.class.getName() });
+		String[] imports = this.importSelector.selectImports(this.annotationMetadata);
+		assertThat(imports.length, is(equalTo(1)));
+	}
+
 	private void configureExclusions(String[] classExclusion, String[] nameExclusion,
 			String[] propertyExclusion) {
 		given(
@@ -168,4 +180,5 @@ public class EnableAutoConfigurationImportSelectorTests {
 		return SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class,
 				getClass().getClassLoader());
 	}
+
 }

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/context/ConfigurationPropertiesAutoConfigurationTests.java

@@ -18,9 +18,11 @@ package org.springframework.boot.autoconfigure.context;
 
 import org.junit.After;
 import org.junit.Test;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.test.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Configuration;
 import org.springframework.stereotype.Component;
 
 import static org.hamcrest.core.Is.is;
@@ -44,8 +46,7 @@ public class ConfigurationPropertiesAutoConfigurationTests {
 
 	@Test
 	public void processAnnotatedBean() {
-		load(new Class[] { SampleBean.class,
-				ConfigurationPropertiesAutoConfiguration.class }, "foo.name:test");
+		load(new Class[] { AutoConfigured.class, SampleBean.class }, "foo.name:test");
 		assertThat(this.context.getBean(SampleBean.class).getName(), is("test"));
 	}
 
@@ -62,6 +63,12 @@ public class ConfigurationPropertiesAutoConfigurationTests {
 		this.context.refresh();
 	}
 
+	@Configuration
+	@EnableAutoConfiguration(include = ConfigurationPropertiesAutoConfiguration.class)
+	static class AutoConfigured {
+
+	}
+
 	@Component
 	@ConfigurationProperties("foo")
 	static class SampleBean {