Introduce tests for SpEL PropertyAccessor ordering

Closes gh-33861

spring-expression/src/test/java/org/springframework/expression/spel/ast/AstUtilsTests.java

@@ -0,0 +1,170 @@
+/*
+ * Copyright 2002-2024 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.ast;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.expression.EvaluationContext;
+import org.springframework.expression.PropertyAccessor;
+import org.springframework.expression.TypedValue;
+import org.springframework.lang.Nullable;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link AstUtils}.
+ *
+ * @author Sam Brannen
+ * @since 6.1.15
+ */
+class AstUtilsTests {
+
+	private final PropertyAccessor animal1Accessor = createAccessor("Animal1", Animal.class);
+
+	private final PropertyAccessor animal2Accessor = createAccessor("Animal2", Animal.class);
+
+	private final PropertyAccessor cat1Accessor = createAccessor("Cat1", Cat.class);
+
+	private final PropertyAccessor cat2Accessor = createAccessor("Cat2", Cat.class);
+
+	private final PropertyAccessor generic1Accessor = createAccessor("Generic1", null);
+
+	private final PropertyAccessor generic2Accessor = createAccessor("Generic2", null);
+
+	private final List<PropertyAccessor> accessors = List.of(
+			generic1Accessor,
+			cat1Accessor,
+			animal1Accessor,
+			animal2Accessor,
+			cat2Accessor,
+			generic2Accessor
+		);
+
+
+	@Test
+	void emptyAccessorsList() {
+		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(new Cat(), List.of());
+		assertThat(accessorsToTry).isEmpty();
+	}
+
+	@Test
+	void noMatch() {
+		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(new Dog(), List.of(cat1Accessor));
+		assertThat(accessorsToTry).isEmpty();
+	}
+
+	@Test
+	void singleExactTypeMatch() {
+		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(new Cat(), List.of(cat1Accessor));
+		assertThat(accessorsToTry).containsExactly(cat1Accessor);
+	}
+
+	@Test
+	void exactTypeMatches() {
+		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(new Cat(), accessors);
+		// We would actually expect the following.
+		// assertThat(accessorsToTry).containsExactly(
+		// 		cat1Accessor, cat2Accessor, animal1Accessor, animal2Accessor, generic1Accessor, generic2Accessor);
+		// However, prior to Spring Framework 6.2, the supertype and generic accessors are not
+		// ordered properly. So we test that the exact matches come first and in the expected order.
+		assertThat(accessorsToTry)
+				.hasSize(accessors.size())
+				.startsWith(cat1Accessor, cat2Accessor);
+	}
+
+	@Disabled("PropertyAccessor ordering for supertype and generic matches is broken prior to Spring Framework 6.2")
+	@Test
+	void supertypeMatches() {
+		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(new Dog(), accessors);
+		assertThat(accessorsToTry).containsExactly(
+				animal1Accessor, animal2Accessor, generic1Accessor, generic2Accessor);
+	}
+
+	@Test
+	void genericMatches() {
+		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry("not an Animal", accessors);
+		assertThat(accessorsToTry).containsExactly(generic1Accessor, generic2Accessor);
+	}
+
+
+	private static PropertyAccessor createAccessor(String name, Class<?> type) {
+		return new DemoAccessor(name, type);
+	}
+
+	private static List<PropertyAccessor> getPropertyAccessorsToTry(Object target, List<PropertyAccessor> propertyAccessors) {
+		return AstUtils.getPropertyAccessorsToTry(target.getClass(), propertyAccessors);
+	}
+
+
+	private static class DemoAccessor implements PropertyAccessor {
+
+		private final String name;
+		private final Class<?>[] types;
+
+		DemoAccessor(String name, Class<?> type) {
+			this.name = name;
+			this.types = (type != null ? new Class<?>[] {type} : null);
+		}
+
+		@Override
+		@Nullable
+		public Class<?>[] getSpecificTargetClasses() {
+			return this.types;
+		}
+
+		@Override
+		public String toString() {
+			return this.name;
+		}
+
+		@Override
+		public boolean canRead(EvaluationContext context, Object target, String name) {
+			return true;
+		}
+
+		@Override
+		public TypedValue read(EvaluationContext context, Object target, String name) {
+			throw new UnsupportedOperationException("Auto-generated method stub");
+		}
+
+		@Override
+		public boolean canWrite(EvaluationContext context, Object target, String name) {
+			return false;
+		}
+
+		@Override
+		public void write(EvaluationContext context, Object target, String name, Object newValue) {
+			/* no-op */
+		}
+	}
+
+	sealed interface Animal permits Bat, Cat, Dog {
+	}
+
+	static final class Bat implements Animal {
+	}
+
+	static final class Cat implements Animal {
+	}
+
+	static final class Dog implements Animal {
+	}
+
+}