Split migration from Log4j 1 to Log4j 2 API and Log4j 2 Core

What problem are you trying to solve?

The Migrate Log4j 1.x to Log4j 2.x recipe, provides steps that:

• migrate usages of Log4j 1 in code to usages of Log4j 2 API,
• migrate the logging backend from Log4j 1 to Log4j 2 Core, which only involves changes to Maven or Gradle dependencies.

The second set of migration rules could be refactored into a separate (and faster) recipe.

Nowadays most applications don't use Log4j API in their code: since 2002 JCL and SLF4J have replaced the usage of Log4j 1 in code almost entirely.
However there is a niche of users that kept using Log4j 1 (and its clone Reload4J) as logging backend. These users might be interested in a recipe that only reconfigures their runtime classpath and converts their configuration files.

Describe the solution you'd like

I would like to move the rules that change dependencies from the Log4j1ToLog4j2 recipe to a new Log4j1ToLog4j2Core recipe and use the latter in the former.

Are you interested in contributing this feature to OpenRewrite?

I will contribute this feature in late Q3 2023, enhanced with a Log4j 1 to Log4j 2 configuration format converter.

Start by reading the Log4j1ToLog4j2 recipe at the linked documentation page and identify the rules that change Maven or Gradle dependencies. Move those rules into a Log4j1ToLog4j2Core recipe and have the original recipe use it. Done means backend-only migration can run separately while the existing recipe retains its full behavior.