krallus commented on PR #1441: URL: https://github.com/apache/logging-log4j2/pull/1441#issuecomment-2276619307
Yes, my IDE flags the XML as having errors if I use the XSD at https://logging.apache.org/xml/ns/log4j-config-2.xsd when I have any property substitution. I think property substitution in Log4j XML configurations is probably quite common. I do it in many places. I just provided a simple example. Personally, I would be in favour of making all attributes be of type `xsd:string`. Not only is there property substitution to consider, but there may be other valid values that the XSD simply will not be aware of. For example, in the case of "level", the documentation in the XSD itself has documentation, _"NOTE: The Log4j API supports custom levels, the following list contains only the standard ones."_. There is still great utility in having an XSD both validate the structure of all of the elements and required attributes, as well as XML authoring assistance in an IDE, just not for attribute values. However, there is a way to define an XSD that will grant both IDE guidance for attribute values *and* allow for any string at the expense of slightly more sophistication in the XSD. Here is an oversimplified example just to demonstrate how this can be done. Example XSD file that allows a list for IDE guidance but will also validate any string. Note the "levelOrSubstitution" type: ```xsd <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"; elementFormDefault="qualified"> <xs:simpleType name="levelOrSubstitution"> <xs:union> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="TRACE" /> <xs:enumeration value="DEBUG" /> <xs:enumeration value="INFO" /> <xs:enumeration value="WARN" /> </xs:restriction> </xs:simpleType> <xs:simpleType> <xs:restriction base="xs:string"> <xs:pattern value=".+" /> </xs:restriction> </xs:simpleType> </xs:union> </xs:simpleType> <!-- Root element definition --> <xs:element name="Configuration"> <xs:complexType> <xs:sequence> <xs:element name="Root"> <xs:complexType> <xs:sequence> <xs:element name="AppenderRef"> <xs:complexType> <xs:attribute name="ref" type="xs:string" use="required" /> </xs:complexType> </xs:element> </xs:sequence> <xs:attribute name="level" type="levelOrSubstitution" use="required" /> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:schema> ``` Valid XML File: ```xml <?xml version="1.0" encoding="UTF-8"?> <Configuration xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; xsi:noNamespaceSchemaLocation="testconfig.xsd"> <Root level="${sys:myapp.root.logging.level:-${sys:rootLogger.level:-WARN}}"> <AppenderRef ref="FileRfc5424Inspired" /> </Root> </Configuration> ``` Eclipse IDE guidance when filling out the XML: _(Ignore the first grey line as it is simply an informative artifact that did not refresh after I renamed the XSD)_  Note that for the `xs:pattern`, I considered using a pattern that would match only on `${...}` instead of any string, but that is not general enough. Consider `fileName="knownPath/${someDerivedName}.ext"`. I hope that helps some. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
