MethodReference treats proxy-targeting expressions as non-compilable

Issue: SPR-16191

(cherry picked from commit c30145d)

Author: jhoeller

spring-expression/src/main/java/org/springframework/expression/spel/ast/MethodReference.java

@@ -19,6 +19,7 @@
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.lang.reflect.Proxy;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -257,7 +258,8 @@ public String toStringAST() {
 	@Override
 	public boolean isCompilable() {
 		CachedMethodExecutor executorToCheck = this.cachedExecutor;
-		if (executorToCheck == null || !(executorToCheck.get() instanceof ReflectiveMethodExecutor)) {
+		if (executorToCheck == null || executorToCheck.hasProxyTarget() ||
+				!(executorToCheck.get() instanceof ReflectiveMethodExecutor)) {
 			return false;
 		}
 
@@ -271,8 +273,7 @@ public boolean isCompilable() {
 		if (executor.didArgumentConversionOccur()) {
 			return false;
 		}
-		Method method = executor.getMethod();
-		Class<?> clazz = method.getDeclaringClass();
+		Class<?> clazz = executor.getMethod().getDeclaringClass();
 		if (!Modifier.isPublic(clazz.getModifiers()) && executor.getPublicDeclaringClass() == null) {
 			return false;
 		}
@@ -385,6 +386,10 @@ public boolean isSuitable(Object value, TypeDescriptor target, List<TypeDescript
 					this.target.equals(target) && this.argumentTypes.equals(argumentTypes));
 		}
 
+		public boolean hasProxyTarget() {
+			return (this.target != null && Proxy.isProxyClass(this.target.getType()));
+		}
+
 		public MethodExecutor get() {
 			return this.methodExecutor;
 		}

spring-expression/src/test/java/org/springframework/expression/spel/SpelReproTests.java

@@ -724,13 +724,32 @@ public void varargsAgainstProxy_SPR16122() {
 
 		VarargsReceiver receiver = new VarargsReceiver();
 		VarargsInterface proxy = (VarargsInterface) Proxy.newProxyInstance(
-				getClass().getClassLoader(), new Class<?>[]{VarargsInterface.class},
+				getClass().getClassLoader(), new Class<?>[] {VarargsInterface.class},
 				(proxy1, method, args) -> method.invoke(receiver, args));
 
 		assertEquals("OK", expr.getValue(new StandardEvaluationContext(receiver)));
 		assertEquals("OK", expr.getValue(new StandardEvaluationContext(proxy)));
 	}
 
+	@Test
+	public void testCompiledExpressionForProxy_SPR16191() {
+		SpelExpressionParser expressionParser =
+				new SpelExpressionParser(new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE, null));
+		Expression expression = expressionParser.parseExpression("#target.process(#root)");
+
+		VarargsReceiver receiver = new VarargsReceiver();
+		VarargsInterface proxy = (VarargsInterface) Proxy.newProxyInstance(
+				getClass().getClassLoader(), new Class<?>[] {VarargsInterface.class},
+				(proxy1, method, args) -> method.invoke(receiver, args));
+
+		StandardEvaluationContext evaluationContext = new StandardEvaluationContext();
+		evaluationContext.setVariable("target", proxy);
+
+		String result = expression.getValue(evaluationContext, "foo", String.class);
+		result = expression.getValue(evaluationContext, "foo", String.class);
+		assertEquals("OK", result);
+	}
+
 	@Test
 	public void varargsAndPrimitives_SPR8174() throws Exception {
 		EvaluationContext emptyEvalContext = new StandardEvaluationContext();