Add support for Eclipse Clean Up

From my understanding Spotless uses org.eclipse.jdt:org.eclipse.jdt.core to do formatting with Eclipse. Currently this only provides whitespace changes, but Eclipse itself also has Clean Up which makes code changes. I think this functionality is provided by the org.eclipse.jdt:org.eclipse.jdt.ui package. Would it be possible to also add this functionality to Spotless?

[bwRavencl]

+1 from me as well! This would really take Spotless to the next level!

[fvgh]

@HoldYourWaffle You should read the Spotless contribution guide first.

The Eclipse formatter is part of the _ext.

We obtain the Eclispe JDT parts from MavenCentral. I expect Clean-Up to be part of the JDT core code, so the current setup of the spotless-eclipse-jdt should be sufficient for this task.

I always use Eclipse for coding, but since you don’t need to care about the Eclipse plugins and the OSGI layer, InelliJ should also work fine. Since MavenCentral also provides the Java source bundles for JDT, debugging your code should not be problematic. Please have a look at the existing tests. Try to run them in your IDE and step down to the Eclipse code.

All Spotless Eclipse formatter basically just do the following:

• Setup framework
• Configure the Eclipse formatters
• Provide a function which call the Eclipse formatters

Don’t worry too much about the underlying Eclipse framework. I think the the current SpotlessEclipseFramwork setup should be sufficient. Eclipse uses OSGI and JDT is just a plugin. Since we don’t want the full Eclipse environment, our framework just stubs out most of the Eclipse framework functionality.

So in the end you just have to find the JDT method for the clean-up and how to configure it. Add the configuration to the EclipseJdtFormatterStepImpl constructor and an additional call to the format method. Please add some unit tests. Most Eclipse formatters look quite similar. This CSS Clean-UP example might give you a hint, what you should look for.

Afterwards we can talk about remaining issues (documentation, default configuration, …). As Ned pointed out, not all clean-up functionality can work with Spotless, since Spotless only knows the content of a single file and not the project structure. Hence some configuration option must be suppressed.