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Intellij Plugin breaks method inlining and variable extraction from inside if condition

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
java
Domain
developer-experience, tooling

Research direction

Start with the Java reproduction in the issue and investigate the IntelliJ plugin's formatting interaction with method inlining and variable extraction inside an if condition. Reproduce the transformation with the plugin enabled and compare it with the disabled result; done means the refactoring no longer inserts an unnecessary if (true), reports an error, or leaves formatting broken.

Written by the indexing model from the issue text.

Description

IntelliJ

Consider the following code and try inlining isEmpty2:

import java.util.Collection;
import java.util.List;

public class InliningWithJavaFormat {
  static boolean isEmpty(Collection<?> c) {
    return c == null || c.isEmpty();
  }

  static boolean isEmpty2(Collection<?> c) {
    return isEmpty(c);
  }

  public static void main(String[] args){
    var pojo = new MyPojo();
    if (pojo != null && !isEmpty2(pojo.getCollection())) {
      System.out.println("empty");
    }
  }

  static class MyPojo {
    Collection<String> getCollection() {
      return List.of();
    }
  }
}

Not only does it fail (without reporting it), but it adds an additional if (true):

  public static void main(String[] args){
    var pojo = new MyPojo();
    if (pojo != null && !isEmpty2(pojo.getCollection())) {
      if (true) {
        System.out.println("empty");
      }
    }
  }

with the plugin disabled, it works:

  public static void main(String[] args){
    var pojo = new MyPojo();
    if (pojo != null) {
      Collection<?> c = pojo.getCollection();
      if (!isEmpty(c)) {
        System.out.println("empty");
      }
    }
  }

(not the ideal result but at least it does not fail)

In addition, when I do that on my actual project I get an error notification from the plugin and the formatting gets broken:
error notification
(I did not try to reproduce this with an MRE, I guess it is a side effect of the first issue)

Dominant language
Java
Stars
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Avg merge
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Merged PRs (30d)
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Getting set up

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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