When using an <extends> element without a location attribute an unnecessary warning is output stating that ../ivy.xml could not be parsed (unless there is in fact a file ../ivy.xml relative to the ivy.xml that contains the <extends>).
XmlModuleDescriptorParser.extendsStarted() is the source of the warning. If no location was specified on the <extends> it uses a default location of ../ivy.xml. It then attempts to find and use the ../ivy.xml location, and only falls back to resolving the parent descriptor if ../ivy.xml doesn't exist or if its ModuleId is not what is expected.
The behavior is sensible and I do not suggest that it be changed. However, it would be nice if the warning that ../ivy.xml could not be parsed were suppressed when that file is being used as a default. The warning would still be appropriate if location="../ivy.xml" were explicitly included in the <extends> element.