Fix mutually exclusive use of CachePut and Cacheable

Commit eea230f introduced a regression by adding a support for the
"result" variable in SpEL expression for @CachePut. As such expressions
cannot be evaluated upfront anymore, any method that contains both
@Cacheable and @CachePut annotations are always executed even when
their conditions are mutually exclusive.

This is an example of such mutual exclusion

@Cacheable(condition = "#p1", key = "#p0")
@CachePut(condition = "!#p1", key = "#p0")
public Object getFooById(Object id, boolean flag) { ... }

This commit updates CacheEvaluationContext to define a set of
unavailable variables. When such variable is accessed for a given
expression, an exception is thrown. This is used to restore the
evaluation of the @CachePut condition upfront by registering "result"
as an unavailable variable.

If all @CachePut operations have been excluded by this upfront check,
the @Cacheable operation is processed as it was before. Such upfront
check restore the behavior prior to eea230f.

Issue: SPR-11955

spring-context/src/test/java/org/springframework/cache/interceptor/CachePutEvaluationTests.java

@@ -0,0 +1,146 @@
+/*
+ * Copyright 2002-2014 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.cache.interceptor;
+
+import static org.junit.Assert.*;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import org.springframework.cache.Cache;
+import org.springframework.cache.CacheManager;
+import org.springframework.cache.annotation.CacheConfig;
+import org.springframework.cache.annotation.CachePut;
+import org.springframework.cache.annotation.Cacheable;
+import org.springframework.cache.annotation.CachingConfigurerSupport;
+import org.springframework.cache.annotation.EnableCaching;
+import org.springframework.cache.concurrent.ConcurrentMapCacheManager;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Tests corner case of using {@link Cacheable} and  {@link CachePut} on the
+ * same operation.
+ *
+ * @author Stephane Nicoll
+ */
+public class CachePutEvaluationTests {
+
+	private ConfigurableApplicationContext context;
+
+	private Cache cache;
+
+	private SimpleService service;
+
+	@Before
+	public void setup() {
+		this.context = new AnnotationConfigApplicationContext(Config.class);
+		this.cache = context.getBean(CacheManager.class).getCache("test");
+		this.service = context.getBean(SimpleService.class);
+	}
+
+	@After
+	public void close() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	public void mutualGetPutExclusion() {
+		String key = "1";
+
+		Long first = service.getOrPut(key, true);
+		Long second = service.getOrPut(key, true);
+		assertSame(first, second);
+
+		// This forces the method to be executed again
+		Long expected = first + 1;
+		Long third = service.getOrPut(key, false);
+		assertEquals(expected, third);
+
+		Long fourth = service.getOrPut(key, true);
+		assertSame(third, fourth);
+	}
+
+	@Test
+	public void getAndPut() {
+		cache.clear();
+
+		long key = 1;
+		Long value = service.getAndPut(key);
+
+		assertEquals("Wrong value for @Cacheable key", value, cache.get(key).get());
+		assertEquals("Wrong value for @CachePut key", value, cache.get(value + 100).get()); // See @CachePut
+
+		// CachePut forced a method call
+		Long anotherValue = service.getAndPut(key);
+		assertNotSame(value, anotherValue);
+		// NOTE: while you might expect the main key to have been updated, it hasn't. @Cacheable operations
+		// are only processed in case of a cache miss. This is why combining @Cacheable with @CachePut
+		// is a very bad idea. We could refine the condition now that we can figure out if we are going
+		// to invoke the method anyway but that brings a whole new set of potential regressions.
+		//assertEquals("Wrong value for @Cacheable key", anotherValue, cache.get(key).get());
+		assertEquals("Wrong value for @CachePut key", anotherValue, cache.get(anotherValue + 100).get());
+	}
+
+	@Configuration
+	@EnableCaching
+	static class Config extends CachingConfigurerSupport {
+
+		@Bean
+		@Override
+		public CacheManager cacheManager() {
+			return new ConcurrentMapCacheManager();
+		}
+
+		@Bean
+		public SimpleService simpleService() {
+			return new SimpleService();
+		}
+
+	}
+
+	@CacheConfig(cacheNames = "test")
+	public static class SimpleService {
+		private AtomicLong counter = new AtomicLong();
+
+		/**
+		 * Represent a mutual exclusion use case. The boolean flag exclude one of the two operation.
+		 */
+		@Cacheable(condition = "#p1", key = "#p0")
+		@CachePut(condition = "!#p1", key = "#p0")
+		public Long getOrPut(Object id, boolean flag) {
+			return counter.getAndIncrement();
+		}
+
+		/**
+		 * Represent an invalid use case. If the result of the operation is non null, then we put
+		 * the value with a different key. This forces the method to be executed every time.
+		 */
+		@Cacheable
+		@CachePut(key = "#result + 100", condition = "#result != null")
+		public Long getAndPut(long id) {
+			return counter.getAndIncrement();
+		}
+	}
+}

spring-context/src/test/java/org/springframework/cache/interceptor/ExpressionEvaluatorTests.java

@@ -21,9 +21,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
 
-import org.junit.Rule;
 import org.junit.Test;
-import org.junit.rules.ExpectedException;
 import org.springframework.cache.annotation.AnnotationCacheOperationSource;
 import org.springframework.cache.annotation.Cacheable;
 import org.springframework.cache.annotation.Caching;
@@ -43,9 +41,6 @@ import static org.junit.Assert.*;
  */
 public class ExpressionEvaluatorTests {
 
-	@Rule
-	public ExpectedException thrown = ExpectedException.none();
-
 	private ExpressionEvaluator eval = new ExpressionEvaluator();
 
 	private AnnotationCacheOperationSource source = new AnnotationCacheOperationSource();
@@ -113,6 +108,18 @@ public class ExpressionEvaluatorTests {
 		assertThat(value, nullValue());
 	}
 
+	@Test
+	public void unavailableReturnValue() throws Exception {
+		EvaluationContext context = createEvaluationContext(ExpressionEvaluator.RESULT_UNAVAILABLE);
+		try {
+			new SpelExpressionParser().parseExpression("#result").getValue(context);
+			fail("Should have failed to parse expression, result not available");
+		}
+		catch (VariableNotAvailableException e) {
+			assertEquals("wrong variable name", "result", e.getName());
+		}
+	}
+
 	private EvaluationContext createEvaluationContext(Object result) {
 		AnnotatedClass target = new AnnotatedClass();
 		Method method = ReflectionUtils.findMethod(AnnotatedClass.class, "multipleCaching", Object.class,