Dummy Error Prone check that does extra AST traversals

TestPasses.java

package testpasses;

import com.google.auto.service.AutoService;
import com.google.errorprone.BugPattern;
import com.google.errorprone.ErrorProneFlags;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker;
import com.google.errorprone.matchers.Description;
import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.util.TreeScanner;

import static com.google.errorprone.BugPattern.Category.ONE_OFF;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;

@AutoService(BugChecker.class)
@BugPattern(
  name = "TestPasses",
  summary = "Testing performance cost of many passes",
  category = ONE_OFF,
  severity = WARNING
)
public class TestPasses extends BugChecker
    implements BugChecker.CompilationUnitTreeMatcher {

  final int numScans;

  public TestPasses() {
    this(ErrorProneFlags.empty());
  }

  public TestPasses(ErrorProneFlags flags) {
    numScans = flags.get("TestPasses:NumScans").map(Integer::parseInt).orElse(1);
  }
  @Override
  public Description matchCompilationUnit(CompilationUnitTree tree,
      VisitorState state) {
    for (int i = 0; i < numScans; i++) {
      (new DummyScanner()).scan(tree, null);
    }
    return Description.NO_MATCH;
  }

  private static class DummyScanner extends TreeScanner<Void, Void> {
  }
}