Support compilation of array and list indexing with Integer in SpEL

Prior to this commit, the Spring Expression Language (SpEL) failed to
compile an expression that indexed into any array or list using an
Integer.

This commit adds support for compilation of such expressions by
ensuring that an Integer is unboxed into an int in the compiled
bytecode.

See gh-32694
Closes gh-32908

Author: sbrannen

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

@@ -221,6 +221,8 @@ public void generateCode(MethodVisitor mv, CodeFlow cf) {
 			cf.loadTarget(mv);
 		}
 
+		SpelNodeImpl index = this.children[0];
+
 		if (this.indexedType == IndexedType.ARRAY) {
 			String exitTypeDescriptor = this.exitTypeDescriptor;
 			Assert.state(exitTypeDescriptor != null, "Array not compilable without descriptor");
@@ -266,32 +268,27 @@ public void generateCode(MethodVisitor mv, CodeFlow cf) {
 				}
 			};
 
-			SpelNodeImpl index = this.children[0];
-			cf.enterCompilationScope();
-			index.generateCode(mv, cf);
-			cf.exitCompilationScope();
+			generateIndexCode(mv, cf, index, int.class);
 			mv.visitInsn(insn);
 		}
 
 		else if (this.indexedType == IndexedType.LIST) {
 			mv.visitTypeInsn(CHECKCAST, "java/util/List");
-			cf.enterCompilationScope();
-			this.children[0].generateCode(mv, cf);
-			cf.exitCompilationScope();
+			generateIndexCode(mv, cf, index, int.class);
 			mv.visitMethodInsn(INVOKEINTERFACE, "java/util/List", "get", "(I)Ljava/lang/Object;", true);
 		}
 
 		else if (this.indexedType == IndexedType.MAP) {
 			mv.visitTypeInsn(CHECKCAST, "java/util/Map");
 			// Special case when the key is an unquoted string literal that will be parsed as
 			// a property/field reference
-			if ((this.children[0] instanceof PropertyOrFieldReference reference)) {
+			if ((index instanceof PropertyOrFieldReference reference)) {
 				String mapKeyName = reference.getName();
 				mv.visitLdcInsn(mapKeyName);
 			}
 			else {
 				cf.enterCompilationScope();
-				this.children[0].generateCode(mv, cf);
+				index.generateCode(mv, cf);
 				cf.exitCompilationScope();
 			}
 			mv.visitMethodInsn(
@@ -328,6 +325,11 @@ else if (this.indexedType == IndexedType.OBJECT) {
 		cf.pushDescriptor(this.exitTypeDescriptor);
 	}
 
+	private void generateIndexCode(MethodVisitor mv, CodeFlow cf, SpelNodeImpl indexNode, Class<?> indexType) {
+		String indexDesc = CodeFlow.toDescriptor(indexType);
+		generateCodeForArgument(mv, cf, indexNode, indexDesc);
+	}
+
 	@Override
 	public String toStringAST() {
 		return "[" + getChild(0).toStringAST() + "]";

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

@@ -671,6 +671,32 @@ void indexIntoObject() {
 			assertThat(getAst().getExitDescriptor()).isEqualTo("Ljava/lang/String");
 		}
 
+		@Test  // gh-32694, gh-32908
+		void indexIntoArrayUsingIntegerWrapper() {
+			context.setVariable("array", new int[] {1, 2, 3, 4});
+			context.setVariable("index", 2);
+
+			expression = parser.parseExpression("#array[#index]");
+
+			assertThat(expression.getValue(context)).isEqualTo(3);
+			assertCanCompile(expression);
+			assertThat(expression.getValue(context)).isEqualTo(3);
+			assertThat(getAst().getExitDescriptor()).isEqualTo("I");
+		}
+
+		@Test  // gh-32694, gh-32908
+		void indexIntoListUsingIntegerWrapper() {
+			context.setVariable("list", List.of(1, 2, 3, 4));
+			context.setVariable("index", 2);
+
+			expression = parser.parseExpression("#list[#index]");
+
+			assertThat(expression.getValue(context)).isEqualTo(3);
+			assertCanCompile(expression);
+			assertThat(expression.getValue(context)).isEqualTo(3);
+			assertThat(getAst().getExitDescriptor()).isEqualTo("Ljava/lang/Object");
+		}
+
 		private String stringify(Object object) {
 			Stream<? extends Object> stream;
 			if (object instanceof Collection<?> collection) {