Generation of .java_output files spuriously fails

There are very simple .java tests that nondeterministically either

• Fail to produce a non-empty .out reference file

    class HitboxTest {
  
    public static void main(String[] args) {
  
      Position p = new Position();
      p.x = 100;
      p.y = 50;
  
      Hitbox b = new Hitbox();
      b.x = 160;
      b.y = 90;
      b.w = 30;
      b.h = 20;
  
      while (!b.contains(p)) {
        p.move(2, 1);
      }
      System.out.println(p.x);
      System.out.println(p.y);
    }
  
  }
  
  class Position {
    public int x;
    public int y;
  
    public void move(int xstep, int ystep) {
      x = x + xstep;
      y = y + ystep;
    }
  }
  
  class Hitbox {
    public int x;
    public int y;
    public int w;
    public int h;
  
    public boolean contains(Position p) {
      return p.x >= x && p.x <= x + w && p.y >= y && p.y <= y + h;
    }
  }

• Have strange javac compile errors:

  [FAIL   ] compile:transitive_object_chain.java    invalid java code, but output file missing
  Report for failing test case transitive_object_chain.java
  Invalid java code, but output file missing
  Error code: 1
  Javac error message:
  
  [0001]    transitive_object_chain.java:8: error: non-static variable out cannot be referenced from a static context
  [0002]            System.out.println(a.ref.ref.n);
  [0003]                  ^
  [0004]    transitive_object_chain.java:8: error: method println in class System cannot be applied to given types;
  [0005]            System.out.println(a.ref.ref.n);
  [0006]                      ^
  [0007]      required: no arguments
  [0008]      found: int
  [0009]      reason: actual and formal argument lists differ in length
  [0010]    2 errors
  [0011]
  
  Source file:
  
  [0001]    class transitive_object_chain {
  [0002]        public static void main(String[] args) {
  [0003]            A_2 a = new A_2();
  [0004]            A_2 b = new A_2();
  [0005]            a.ref = b;
  [0006]            b.ref = a;
  [0007]            a.n = 5;
  [0008]            System.out.println(a.ref.ref.n);
  [0009]        }
  [0010]    }
  [0011]
  [0012]    class A_2 {
  [0013]        public A_2 ref;
  [0014]        public int n;
  [0015]    }
  [0016]

You can (hopefully) reproduce this by doing a git clean -fxd in the tests repository, followed by re-running mjtest.

Johannes (@uqddy), maybe you suspect something?