Fix @Autowired+@PostConstruct+@Configuration issue

A subtle issue existed with the way we relied on isCurrentlyInCreation
to determine whether a @Bean method is being called by the container
or by user code.  This worked in most cases, but in the particular
scenario laid out by SPR-8080, this approach was no longer sufficient.

This change introduces a ThreadLocal that contains the factory method
currently being invoked by the container, such that enhanced @Bean
methods can check against it to see if they are being called by the
container or not.  If so, that is the cue that the user-defined @Bean
method implementation should be invoked in order to actually create
the bean for the first time.  If not, then the cached instance of
the already-created bean should be looked up and returned.

See ConfigurationClassPostConstructAndAutowiringTests for
reproduction cases and more detail.

Issue: SPR-8080

org.springframework.context/src/test/java/org/springframework/context/annotation/ConfigurationClassPostConstructAndAutowiringTests.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2002-2011 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
+ *
+ *      http://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.context.annotation;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import javax.annotation.PostConstruct;
+
+import org.junit.Test;
+import org.springframework.beans.TestBean;
+import org.springframework.beans.factory.annotation.Autowired;
+
+/**
+ * Tests cornering the issue reported in SPR-8080. If the product of a @Bean method
+ * was @Autowired into a configuration class while at the same time the declaring
+ * configuration class for the @Bean method in question has a @PostConstruct
+ * (or other initializer) method, the container would become confused about the
+ * 'currently in creation' status of the autowired bean and result in creating multiple
+ * instances of the given @Bean, violating container scoping / singleton semantics.
+ *
+ * This is resolved through no longer relying on 'currently in creation' status, but
+ * rather on a thread local that informs the enhanced bean method implementation whether
+ * the factory is the caller or not.
+ *
+ * @author Chris Beams
+ * @since 3.1
+ */
+public class ConfigurationClassPostConstructAndAutowiringTests {
+
+	/**
+	 * Prior to the fix for SPR-8080, this method would succeed due to ordering of
+	 * configuration class registration.
+	 */
+	@Test
+	public void control() {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+		ctx.register(Config1.class, Config2.class);
+		ctx.refresh();
+
+		assertions(ctx);
+
+		Config2 config2 = ctx.getBean(Config2.class);
+		assertThat(config2.testBean, is(ctx.getBean(TestBean.class)));
+	}
+
+	/**
+	 * Prior to the fix for SPR-8080, this method would fail due to ordering of
+	 * configuration class registration.
+	 */
+	@Test
+	public void originalReproCase() {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+		ctx.register(Config2.class, Config1.class);
+		ctx.refresh();
+
+		assertions(ctx);
+	}
+
+	private void assertions(AnnotationConfigApplicationContext ctx) {
+		Config1 config1 = ctx.getBean(Config1.class);
+		TestBean testBean = ctx.getBean(TestBean.class);
+		assertThat(config1.beanMethodCallCount, is(1));
+		assertThat(testBean.getAge(), is(2));
+	}
+
+
+	@Configuration
+	static class Config1 {
+
+		int beanMethodCallCount = 0;
+
+		@PostConstruct
+		public void init() {
+			beanMethod().setAge(beanMethod().getAge() + 1); // age == 2
+		}
+
+		@Bean
+		public TestBean beanMethod() {
+			beanMethodCallCount++;
+			TestBean testBean = new TestBean();
+			testBean.setAge(1);
+			return testBean;
+		}
+	}
+
+
+	@Configuration
+	static class Config2 {
+		TestBean testBean;
+
+		@Autowired
+		void setTestBean(TestBean testBean) {
+			this.testBean = testBean;
+		}
+	}
+
+}