Mergeable if statements should be combined - RSPEC-S1066

[olwispe]

What's changed?

This PR implements RSPEC-S1066 which was requested in :

• Collapsible if statements should be merged. RSPEC-1066 #45
• Replace nested ifs with one if and conditions joined with && #537

What's your motivation?

Among others, help migrate to pattern matching for instanceof when combined with org.openrewrite.staticanalysis.InstanceOfPatternMatch :

if (o instanceof String) {
  String s = (String) o;
  if (s.isEmpty()) {
     System.out.println("OK");
  }
}

if (o instanceof String s && s.isEmpty()) {
  System.out.println("OK");
}

Anything in particular you'd like reviewers to focus on?

Anyone you would like to review specifically?

@timtebeek

Have you considered any alternatives or workarounds?

Any additional context

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Great to see @olwispe ! Added some light polish and I've been looking at the changes at scale.

Looking at these two examples I wonder if perhaps we should move the inner if conditional to a new line, and keep the comments in more of their original position.

I've pushed a quick test update that shows a comment lost. What are your thoughts to the above proposal?

[olwispe]

Thanks for your comments.
I tend to prefer to have each merged conditional on a new line as you suggest and therefore keep the comments in their original position.