DefaultMergeStrategy - not accounting for AsyncWaitStrategyFactory when merging configurations #3172
Description
DefaultMergeStrategy (Log4j 2.24.1)
I think I may have encountered a potential error if using a CompositeConfiguration.
In the DefaultMergeStrategy#mergeConfigurations, it does a double loop over the source and target node's children - merging from the source into the target.
In these loops it provides special handling for PROPERTIES, SCRIPTS, APPENDERS, FILTERS and LOGGERS.
If the element tag name does not match one of these, the default behaviour is to add the children of the source element to the corresponding target element.
switch (toRootLowerCase(targetChildNode.getName())) {
case PROPERTIES:
case SCRIPTS:
case APPENDERS: { ... }
case LOGGERS: { ... }
default: {
targetChildNode.getChildren().addAll(sourceChildNode.getChildren());
isMerged = true;
break;
}
}
If however, two configurations had an AsyncWaitStrategyFactory element:
<Configuration>
<AsyncWaitStrategyFactory class="a.b.c.Foo">
</Configuration>
<Configuration>
<AsyncWaitStrategyFactory class="d.e.f.Bar">
</Configuration>
This element has no children, and the attributes are not merged.
The 'class' attribute after merging would be taken from the first occurrence a.b.c.Foo and not from the override 'd.e.f.Bar`.
I'll admit I have not tested this scenario, but reviewing the code it logically seems like it might cause a problem
NOTE: "Properties", "Scripts", "Appenders", "Filter" and "Loggers" are all collection elements and have no attributes - so it makes sense that for these no attributes are merged, but the default behavior should IMHO handle the possiblity of attributes and perform a merge of the element's attributes similar to that of the DefaultMergeStrategy#mergeRootProperties method.