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Posted to dev@logging.apache.org by "jorge683 (via GitHub)" <gi...@apache.org> on 2025/05/27 19:51:59 UTC
[D] Attribute 'additivity' is not allowed to appear in element 'Logger' [logging-log4j2]
GitHub user jorge683 created a discussion: Attribute 'additivity' is not allowed to appear in element 'Logger'
According to https://logging.apache.org/xml/ns/log4j-config-2.23.1.xsd , "additivity" is not allowed in "Logger." This is why I'm receiving a WARN from my IDE. Is this a bug?
GitHub link: https://github.com/apache/logging-log4j2/discussions/3696
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Re: [D] Attribute 'additivity' is not allowed to appear in element 'Logger' [logging-log4j2]
Posted by "ppkarwasz (via GitHub)" <gi...@apache.org>.
GitHub user ppkarwasz added a comment to the discussion: Attribute 'additivity' is not allowed to appear in element 'Logger'
Hi @jorge683,
Yes, this is indeed a bug — tracked here: apache/logging-log4j-tools#135 — in the [Log4j Docgen tool](https://logging.apache.org/log4j/tools/log4j-docgen.html), which we use to generate the XML Schema from source code.
It's important to note that Log4j configuration files are inherently **schema-less** by design. Here’s why:
* **Extensibility via Plugins**: Log4j Core is highly extensible — all components are implemented as [Log4j Plugins](https://logging.apache.org/log4j/2.x/manual/plugins.html). This means users can define custom plugins that the official schema won’t recognize. The published schema only includes plugins maintained by the Apache Logging Services project.
* **Conditional Configuration with Arbiters**: Log4j supports a feature called [arbiters](https://logging.apache.org/log4j/2.x/manual/configuration.html#arbiters), which allows XML elements to be conditionally included at runtime. Because arbiters can introduce arbitrary structure, we’ve chosen to exclude them from the schema entirely — they simply can’t be reliably validated.
* **Property Substitution in Attributes**: XML attributes in Log4j configurations always accept [property substitution expressions](https://logging.apache.org/log4j/2.x/manual/configuration.html#property-substitution), which are evaluated at configuration time. Technically, this means all attributes must be treated as strings, which limits the benefits of schema-based validation or IDE auto-completion. A user proposed using XML union types as a workaround (see [apache/logging-log4j-tools#136](https://github.com/apache/logging-log4j-tools/issues/136)), but this hasn’t yet been implemented.
Because of these limitations, XML validation errors in Log4j configuration files should be taken with a grain of salt — your configuration may be perfectly valid and still trigger schema validation errors. Conversely, a configuration that passes validation might still fail at runtime if the required [Log4j Core component JARs](https://logging.apache.org/log4j/2.x/components.html) are missing.
In the long term, we’re considering simplifying the schema generation process to allow users to generate a tailored XML Schema based on the specific Log4j libraries available at runtime. This would improve both the accuracy and usefulness of schema validation in real-world setups. Unfortunately, we currently don't have the bandwidth to implement this, but community contributions to improve Log4j Docgen are always welcome!
GitHub link: https://github.com/apache/logging-log4j2/discussions/3696#discussioncomment-13308231
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Re: [D] Attribute 'additivity' is not allowed to appear in element 'Logger' [logging-log4j2]
Posted by "vy (via GitHub)" <gi...@apache.org>.
GitHub user vy added a comment to the discussion: Attribute 'additivity' is not allowed to appear in element 'Logger'
> Because of these limitations, XML validation errors in Log4j configuration files should be taken with a grain of salt
@ppkarwasz, this is a very nice and elaborate response. I think users would find it helpful to have a (diet version of?) this explanation in [the XML configuration features](https://logging.apache.org/log4j/2.x/manual/configuration.html#xml-features) page. AFAICT, the message we will get across should be _"Use XML and XSD – this is the recommended combo. Yet be aware that XSD is neither exhaustive, nor 100% accurate."_
GitHub link: https://github.com/apache/logging-log4j2/discussions/3696#discussioncomment-13352325
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