BATCH-1139: Add requirement that standalone <tasklet/> be abstract. Otherwise users might think that they can use <step tasklet="?"/> to refer to it. They must always use <tasklet parent="?"/>.

spring-batch-core/src/main/java/org/springframework/batch/core/configuration/xml/TopLevelTaskletElementParser.java

@@ -34,6 +34,11 @@ public class TopLevelTaskletElementParser extends AbstractBeanDefinitionParser {
 	@Override
 	protected AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
 
+		if (!Boolean.valueOf(element.getAttribute("abstract"))) {
+			parserContext.getReaderContext().error(
+					"The <tasklet/> element, when not contained with a <step/>, must be abstract", element);
+		}
+
 		return taskletElementParser.parse(element, parserContext);
 
 	}