Issue with logstash-logback-encoder 8.1+ and shaded Logback classes (ICCE)

[stefan-so-elo]

Hello.

When using logstash-logback-encoder starting from version 8.1, the following error occurs at runtime:

Exception in thread "main" java.lang.IncompatibleClassChangeError: Unexpected return type found for PatternLayoutBase.getInstanceConverterMap(), logback-core dependency version is not compatible
    at org.apache.juli.logging.net.logstash.logback.pattern.PatternLayoutCompatibilityUtil.registerConverter(PatternLayoutCompatibilityUtil.java:78)

In our setup, we are using https://github.com/tomcat-slf4j-logback/tomcat10-slf4j-logback, which shades Logback using the Maven Shade Plugin with the following relocation:

<relocation>
    <pattern>ch.qos.logback</pattern>
    <shadedPattern>org.apache.juli.logging.ch.qos.logback</shadedPattern>
</relocation>

Due to this relocation from ch.qos.logback to org.apache.juli.logging.ch.qos.logback, the IncompatibleClassChangeError is triggered.

The root cause appears to be an explicit type check in logstash-logback-encoder that assumes the original Logback package name. In particular, there is a direct reference to:

ch.qos.logback.core.pattern.DynamicConverter

in the following code:

if (valueType.getTypeName().equals("java.lang.String")) {
    /*
     * In logback <= 1.5.12, getInstanceConverterMap() is a Map<String, String>.
     *     key = converter name
     *     value = name of converter class
     */
    putUnchecked(layout.getInstanceConverterMap(), converterName, converterClass.getName());
} else if (valueType.getTypeName().equals("java.util.function.Supplier<ch.qos.logback.core.pattern.DynamicConverter>")) {
    /*
     * In logback >= 1.5.13, getInstanceConverterMap() is a Map<String, Supplier<DynamicConverter>.
     *     key = converter name
     *     value = supplier of converter instances
     *
     * Related issues:
     *     https://github.com/qos-ch/logback/issues/803
     *     https://github.com/qos-ch/logback/issues/931
     *     https://github.com/qos-ch/logback/issues/932
     */
    putUnchecked(layout.getInstanceConverterMap(), converterName, converterSupplier);
} else {
    throw new IncompatibleClassChangeError(
            "Unexpected return type found for PatternLayoutBase.getInstanceConverterMap(), logback-core dependency version is not compatible");
}

Because the class is shaded, this check fails and leads to the ICCE at runtime.

Questions:

Is there a way to make this compatibility check shading-tolerant, for example by avoiding direct class references?

Alternatively, are there recommended approaches to resolve this issue when Logback must be shaded (as required by tomcat10-slf4j-logback)?

Any guidance or suggestions would be greatly appreciated.

Thank you very much.