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String[]::new treated as a complex argument, breaking member chains

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
72/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
java
Domain
tooling

Research direction

Start by tracing how the Java printer classifies method-chain arguments, then compare handling of String[]::new with ArrayList::new in the formatter tests. Add or update a regression case using the input shown; done means formatting leaves the member chain unchanged and the regression test passes.

Written by the indexing model from the issue text.

Description

Prettier-Java 2.11.0

Input:

class A {

  void f() {
    var items = new ArrayList<>();
    items.stream().map(Object::toString).toArray(String[]::new);
    items.stream().map(Object::toString).collect(toCollection(ArrayList::new));
  }
}

Output:

class A {

  void f() {
    var items = new ArrayList<>();
    items
      .stream()
      .map(Object::toString)
      .toArray(String[]::new);
    items.stream().map(Object::toString).collect(toCollection(ArrayList::new));
  }
}

Expected behavior: Unchanged.

An array constructor reference like String[]::new should be treated just like ArrayList::new. Both are just constructor references.

Dominant language
Java
Stars
1.2k
Forks
122
Avg merge
2d 10h
Merged PRs (30d)
35

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