Bug 64849

Tomcat Embedded EL has a bug closely related to one reported and fixed to the core module, issue 64751 "Incomplete module info descriptor". This is the stacktrace:

java.util.ServiceConfigurationError: javax.el.ExpressionFactory: module org.apache.tomcat.embed.el does not declare `uses`
[ERROR] 	at java.base/java.util.ServiceLoader.fail(ServiceLoader.java:588)
[ERROR] 	at java.base/java.util.ServiceLoader.checkCaller(ServiceLoader.java:574)
[ERROR] 	at java.base/java.util.ServiceLoader.<init>(ServiceLoader.java:503)
[ERROR] 	at java.base/java.util.ServiceLoader.load(ServiceLoader.java:1646)
[ERROR] 	at org.apache.tomcat.embed.el@9.0.39/javax.el.ExpressionFactory.getClassNameServices(ExpressionFactory.java:372)
[ERROR] 	at org.apache.tomcat.embed.el@9.0.39/javax.el.ExpressionFactory.discoverClassName(ExpressionFactory.java:330)
[ERROR] 	at org.apache.tomcat.embed.el@9.0.39/javax.el.ExpressionFactory.newInstance(ExpressionFactory.java:134)
[ERROR] 	at org.apache.tomcat.embed.el@9.0.39/javax.el.ExpressionFactory.newInstance(ExpressionFactory.java:86)

Looking at module-info.java and the contents of META-INF/services I think there are two missing lines for this module descriptor; not just the uses clause, but also and the provides clauses. Both of these lines need adding:

uses javax.el.ExpressionFactory;
provides javax.el.ExpressionFactory with org.apache.el.ExpressionFactoryImpl;

Both lines are necessary to recreate the service provider / loader mechanism with the module system; ExpressionFactory has static methods to look up the implementation (as part of the public newInstance method), so the module uses its own provided implementation.