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 an 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

(cherry picked from commit 079d53c)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * 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.
@@ -226,6 +226,8 @@ public void generateCode(MethodVisitor mv, CodeFlow cf) {
 			cf.loadTarget(mv);
 		}
 
+		SpelNodeImpl index = this.children[0];
+
 		if (this.indexedType == IndexedType.ARRAY) {
 			int insn;
 			if ("D".equals(this.exitTypeDescriptor)) {
@@ -262,33 +264,29 @@ else if ("C".equals(this.exitTypeDescriptor)) {
 						//depthPlusOne(exitTypeDescriptor)+"Ljava/lang/Object;");
 				insn = AALOAD;
 			}
-			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)) {
+			if (index instanceof PropertyOrFieldReference) {
 				PropertyOrFieldReference reference = (PropertyOrFieldReference) this.children[0];
 				String mapKeyName = reference.getName();
 				mv.visitLdcInsn(mapKeyName);
 			}
 			else {
 				cf.enterCompilationScope();
-				this.children[0].generateCode(mv, cf);
+				index.generateCode(mv, cf);
 				cf.exitCompilationScope();
 			}
 			mv.visitMethodInsn(
@@ -325,6 +323,11 @@ 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() {
 		StringJoiner sj = new StringJoiner(",", "[", "]");