EmptyBlock removes } else { when the if block was empty, breaking the logic

[valters]

What version of OpenRewrite are you using?

I am using

• Maven plugin 5.35.0
• rewrite-static-analysis 1.11.0

How are you running OpenRewrite?

Maven plugin.
Minimal project to repro the issue: https://github.com/valters/test-openrewrite
Please see steps in readme.

What is the smallest, simplest way to reproduce the problem?

Trying to rewrite code with moderately tricky if logic:

public class WithEmptyBlock {

  public static class Base {
    public boolean isExtended() {
      return false;
    }
  }

  public static class Extender extends Base {

    @Override
    public boolean isExtended() {
      return true;
    }

    public boolean isExtendedClass() {
      return true;
    }

    public boolean isSomeOtherClass() {
      return false;
    }
  }

  public void shouldNotFlipCondition(Base arg) {

    if (arg.isExtended()) {
      if (((Extender) arg).isExtendedClass()
          || ((Extender) arg).isSomeOtherClass()) {
      } else {
        System.out.println("This line should not be executed!");
        throw new RuntimeException("code should not reach here! if you see this, rewrite has messed up.");
      }
    }
  }
}

What did you expect to see?

Either if condition should be inverted, or the else keyword can't be removed.

What did you see instead?

Broken diff after rewrite:

diff --git a/source-problems/src/main/java/ch/vingolds/testopenrewrite/WithEmptyBlock.java b/source-problems/src/main/java/ch/vingolds/testopenrewrite/WithEmptyBlock.java
index 5b4c050..c1a9f75 100644
--- a/source-problems/src/main/java/ch/vingolds/testopenrewrite/WithEmptyBlock.java
+++ b/source-problems/src/main/java/ch/vingolds/testopenrewrite/WithEmptyBlock.java
@@ -29,7 +29,6 @@ public class WithEmptyBlock {
     if (arg.isExtended()) {
       if (((Extender) arg).isExtendedClass()
           || ((Extender) arg).isSomeOtherClass()) {
-      } else {
         System.out.println("This line should not be executed!");
         throw new RuntimeException("code should not reach here! if you see this, rewrite has messed up.");
       }

What is the full stack trace of any errors you encountered?

No error. Just incorrect output.

[timtebeek]

Thanks a lot for the detailed report and reproducer! I think it would be best to turn this into a runnable unit test as seen here, and then work from there on a draft PR.

rewrite-static-analysis/src/test/java/org/openrewrite/staticanalysis/EmptyBlockTest.java

Lines 391 to 417 in 48c94b5

	@Test
	void emptyElseBlock() {
	rewriteRun(
	//language=java
	java(
	"""
	public class A {
	{
	if (true) {
	System.out.println("this");
	} else {
	}
	}
	}
	""",
	"""
	public class A {
	{
	if (true) {
	System.out.println("this");
	}
	}
	}
	"""
	)
	);
	}