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.

Closes gh-32694

Author: sbrannen

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

@@ -416,13 +416,13 @@ public void generateCode(MethodVisitor mv, CodeFlow cf) {
 				default -> AALOAD;
 			};
 
-			generateIndexCode(index, mv, cf);
+			generateIndexCode(index, int.class, mv, cf);
 			mv.visitInsn(insn);
 		}
 
 		else if (this.indexedType == IndexedType.LIST) {
 			mv.visitTypeInsn(CHECKCAST, "java/util/List");
-			generateIndexCode(index, mv, cf);
+			generateIndexCode(index, int.class, mv, cf);
 			mv.visitMethodInsn(INVOKEINTERFACE, "java/util/List", "get", "(I)Ljava/lang/Object;", true);
 		}
 
@@ -473,6 +473,11 @@ private void generateIndexCode(SpelNodeImpl index, MethodVisitor mv, CodeFlow cf
 		cf.exitCompilationScope();
 	}
 
+	private void generateIndexCode(SpelNodeImpl indexNode, Class<?> indexType, MethodVisitor mv, CodeFlow cf) {
+		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

@@ -706,6 +706,32 @@ void indexIntoObject() {
 			assertThat(getAst().getExitDescriptor()).isEqualTo("Ljava/lang/String");
 		}
 
+		@Test  // gh-32694
+		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
+		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) {