Remove redundant dependencies

[timtebeek]

Remove direct dependencies that are also brought in transitively by other direct dependencies.

Intended to be used when introducing spring boot starters to remove the direct dependencies they bring in.

[steve-aom-elliott]

@timtebeek I'm thinking through how using this recipe in conjunction with other recipes that change dependencies may lead to undesirable situations.

Let's say we have a direct dependency W that has a transitive dependency on X, an we also have a direct dependency on X. If we run this recipe, it would presumably remove the direct dependency on X. If we follow that with something that perhaps upgrades W or changes it to Y and that new dependency no longer has a transitive dependency on X. We're potentially going to be in a situation where the code no longer compiles. I don't think we have a particularly generic way for determining that.

I understand we have plenty of ways to get to a similar situation already, though we would probably want to use this recipe rather sparingly as we can't always easily account for all the overlap.

If we only applied clearing out direct redundant dependencies based on those transitively available through our parent, that's a bit more of a focused scenario, at least, which sounds like could be a desired situation.

Still reading through all the code for this

EDIT: Ah, so I'm seeing that it's definitely for an intentioned removal of a specific dependency's transitives, so that alleviates some of the concern.

[steve-aom-elliott]

Would it be worth adding a test example of something like:

...
<dependencies>
  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.17.0</version>
    <exclusions>
      <exclusion>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.17.0</version>
  </dependency>
</dependencies>
...

This may already be implicit due to it using the resolved POM, but could be a nice illustration of that fact.