java.lang.VerifyError is being thrown in specific case

[lpfeup]

java.lang.VerifyError is being thrown with the following code example:

public class Main2 {
	public static void main(String[] args) throws InterruptedException {
		Async.init();
		
		test()
		.thenRun(() -> System.out.println("DONE"))
		.exceptionally(t -> {t.printStackTrace();return null;});
		
		Thread.sleep(1000);
	}
	
	private static CompletableFuture<TestModel[]> getTestModels() {
		return CompletableFuture.completedFuture(new TestModel[] { new TestModel(1), new TestModel(2) });
	}
	
	private static CompletableFuture<Void> test() {
		TestModel[] testModelArr = await(getTestModels());
		String str = "";

		for (TestModel myModel: testModelArr) {
			str += ":" + await(CompletableFuture.completedFuture(myModel.myInt));
			System.out.println(myModel.myInt.doubleValue());
		}

		System.out.println(str);
		
		return CompletableFuture.completedFuture(null);
	}
	
	private static class TestModel {
		public final Integer myInt;
		
		private TestModel(Integer myInt) {
			this.myInt = myInt;
		}
	}
}

With any of the following changes to the test() method, it no longer throws the error:

1. removing System.out.println(myModel.myInt.doubleValue());:

private static CompletableFuture<Void> test() {
	TestModel[] testModelArr = await(getTestModels());
	String str = "";

	for (TestModel myModel: testModelArr) {
		str += ":" + await(CompletableFuture.completedFuture(myModel.myInt));
	}

	System.out.println(str);
	
	return CompletableFuture.completedFuture(null);
}

2. moving up System.out.println(myModel.myInt.doubleValue()); by 1 line:

private static CompletableFuture<Void> test() {
	TestModel[] testModelArr = await(getTestModels());
	String str = "";

	for (TestModel myModel: testModelArr) {
		System.out.println(myModel.myInt.doubleValue());
		str += ":" + await(CompletableFuture.completedFuture(myModel.myInt));
	}

	System.out.println(str);
	
	return CompletableFuture.completedFuture(null);
}

3. converting testModelArr to list for the for loop:

private static CompletableFuture<Void> test() {
	TestModel[] testModelArr = await(getTestModels());
	String str = "";

	for (TestModel myModel: Arrays.asList(testModelArr)) {
		str += ":" + await(CompletableFuture.completedFuture(myModel.myInt));
		System.out.println(myModel.myInt.doubleValue());
	}

	System.out.println(str);
	
	return CompletableFuture.completedFuture(null);
}

Any idea why this is happening in this specific case?

[lpfeup]

Full error detail

Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    main/Main2.async$test(Ljava/util/concurrent/CompletableFuture;[Lmain/Main2$TestModel;Ljava/lang/String;[Lmain/Main2$TestModel;IILjava/lang/Object;Ljava/lang/StringBuilder;ILjava/lang/Object;)Ljava/util/concurrent/CompletableFuture; @181: getfield
  Reason:
    Type 'java/lang/Object' (current frame, stack[1]) is not assignable to 'main/Main2$TestModel'
  Current Frame:
    bci: @181
    flags: { }
    locals: { '[Lmain/Main2$TestModel;', 'java/lang/String', '[Lmain/Main2$TestModel;', integer, integer, 'java/lang/Object' }
    stack: { 'java/io/PrintStream', 'java/lang/Object' }
  Bytecode:
    0x0000000: 1508 aa00 0000 00e9 0000 0000 0000 0002
    0x0000010: 0000 001a 0000 00ce 0000 00d2 b800 7459
    0x0000020: b600 789a 0022 3a06 1906 b800 7db6 0067
    0x0000030: 1906 0101 0103 0301 0111 0001 ba00 8600
    0x0000040: 00b6 0089 b0b6 008d c000 8f4b 1291 4c2a
    0x0000050: 4d2c be3e 0336 0415 041d a200 6a2c 1504
    0x0000060: 323a 05bb 0095 59b7 0096 2bb6 009a 129c
    0x0000070: b600 9a19 05b4 00a0 b800 2759 b600 789a
    0x0000080: 0027 3a07 3a06 1907 b800 7db6 0067 1907
    0x0000090: 2a2b 2c1d 1504 1905 1906 1100 02ba 0086
    0x00000a0: 0000 b600 89b0 b600 8db6 00a3 b600 a74c
    0x00000b0: b200 3719 05b4 00a0 b600 abb6 00ae 8404
    0x00000c0: 01a7 ff96 b200 372b b600 3f01 b800 27b0
    0x00000d0: 2aa7 ff74 1907 2a2b 2c2d 1504 1505 1906
    0x00000e0: 3a05 3604 3e4d 4c4b a7ff bebb 00b5 59b7
    0x00000f0: 00b6 bf
  Stackmap Table:
    full_frame(@28,{Object[#35],Object[#143],Object[#147],Object[#143],Integer,Integer,Object[#4],Object[#149],Integer,Object[#4]},{})
    full_frame(@69,{},{Object[#35]})
    full_frame(@87,{Object[#143],Object[#147],Object[#143],Integer,Integer},{})
    full_frame(@166,{Object[#143],Object[#147],Object[#143],Integer,Integer,Object[#4]},{Object[#149],Object[#35]})
    full_frame(@196,{Object[#143],Object[#147]},{})
    full_frame(@208,{Object[#35],Object[#143],Object[#147],Object[#143],Integer,Integer,Object[#4],Object[#149],Integer,Object[#4]},{})
    full_frame(@212,{Object[#35],Object[#143],Object[#147],Object[#143],Integer,Integer,Object[#4],Object[#149],Integer,Object[#4]},{})
    full_frame(@235,{Object[#35],Object[#143],Object[#147],Object[#143],Integer,Integer,Object[#4],Object[#149],Integer,Object[#4]},{})

        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
        at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
        at java.lang.Class.getMethod0(Class.java:3018)
        at java.lang.Class.getMethod(Class.java:1784)
        at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)

[lpfeup]

Could this be related to #29?

[JoeHegarty]

Yes, it could be related. There are a couple of cases where the generated bytecode is not correct.
Unfortunately I haven't had a chance to look into them.