Support SpEL compilation of interface methods again

Spring Framework 5.1.8 introduced a regression for the compilation of
SpEL expressions referencing a method declared in an interface. An
attempt to compile such an expression resulted in a
SpelEvaluationException caused by an IncompatibleClassChangeError.

This commit fixes this regression by adding explicit support in
ReflectivePropertyAccessor.OptimalPropertyAccessor.generateCode() for
methods declared in interfaces.

Closes gh-24357

spring-expression/src/main/java/org/springframework/expression/spel/support/ReflectivePropertyAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -55,6 +55,7 @@
  * @author Andy Clement
  * @author Juergen Hoeller
  * @author Phillip Webb
+ * @author Sam Brannen
  * @since 3.0
  * @see StandardEvaluationContext
  * @see SimpleEvaluationContext
@@ -765,8 +766,11 @@ public void generateCode(String propertyName, MethodVisitor mv, CodeFlow cf) {
 			}
 
 			if (this.member instanceof Method) {
-				mv.visitMethodInsn((isStatic ? INVOKESTATIC : INVOKEVIRTUAL), classDesc, this.member.getName(),
-						CodeFlow.createSignatureDescriptor((Method) this.member), false);
+				Method method = (Method) this.member;
+				boolean isInterface = method.getDeclaringClass().isInterface();
+				int opcode = (isStatic ? INVOKESTATIC : isInterface ? INVOKEINTERFACE : INVOKEVIRTUAL);
+				mv.visitMethodInsn(opcode, classDesc, method.getName(),
+						CodeFlow.createSignatureDescriptor(method), isInterface);
 			}
 			else {
 				mv.visitFieldInsn((isStatic ? GETSTATIC : GETFIELD), classDesc, this.member.getName(),

spring-expression/src/test/java/org/springframework/expression/spel/standard/SpelCompilerTests.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2002-2020 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
+ *
+ *      https://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.expression.spel.standard;
+
+import java.util.stream.IntStream;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.Ordered;
+import org.springframework.expression.Expression;
+import org.springframework.expression.spel.SpelCompilerMode;
+import org.springframework.expression.spel.SpelParserConfiguration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for the {@link SpelCompiler}.
+ *
+ * @author Sam Brannen
+ * @since 5.1.14
+ */
+class SpelCompilerTests {
+
+	@Test // gh-24357
+	void expressionCompilesWhenMethodComesFromPublicInterface() {
+		SpelParserConfiguration config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE, null);
+		SpelExpressionParser parser = new SpelExpressionParser(config);
+
+		OrderedComponent component = new OrderedComponent();
+		Expression expression = parser.parseExpression("order");
+
+		// Evaluate the expression multiple times to ensure that it gets compiled.
+		IntStream.rangeClosed(1, 5).forEach(i -> assertThat(expression.getValue(component)).isEqualTo(42));
+	}
+
+
+	static class OrderedComponent implements Ordered {
+
+		@Override
+		public int getOrder() {
+			return 42;
+		}
+	}
+
+}