[jdk21/JEP456 ISSUE] jdk21/jep456 433 preview feature

[cboudereau]

It seems that the code compiles (locally only since github action for java does not support yet JDK21) with preview feature of JDK21 but fails when running unit tests:

jdk21:

openjdk 21 2023-09-19
OpenJDK Runtime Environment (build 21+35-2513)
OpenJDK 64-Bit Server VM (build 21+35-2513, mixed mode, sharing)

1. Issue

running clean compile works :

mvn clean compile

while clean test doesn't with the following error:

[ERROR]   SimpleTest.simple:17 ┬╗ Verify Bad local variable type
Exception Details:
  Location:
    io/github/cboudereau/dataseries/Union$Value.compareTo(Lio/github/cboudereau/dataseries/Union$Value;)I @297: aload
  Reason:
    Type top (current frame, locals[9]) is not assignable to reference type
  Current Frame:
    bci: @297
    flags: { }
    locals: { 'io/github/cboudereau/dataseries/Union$Value', 'io/github/cboudereau/dataseries/Union$Value', '[Z', 'io/github/cboudereau/dataseries/Union$Value$Tuple', integer, 'io/github/cboudereau/dataseries/Union$Value$Tuple', top, top, top, top, top, 'io/github/cboudereau/dataseries/Union$Value$Fixed', 'io/github/cboudereau/dataseries/Union$Value', integer, 'io/github/cboudereau/dataseries/Union$Value', integer } 
    stack: { }
  Bytecode:
    0000000: 1278 c000 7a4d bb00 0c59 2a2b b700 0e59
    0000010: b800 1157 4e03 3604 2c05 0454 2d15 04ba
    0000020: 0017 0000 ab00 0000 0000 0014 0000 0001
    0000030: 0000 0000 0000 0022 bb00 1b59 0101 b700
    0000040: 1d2c 0604 54bf 2d3a 0519 052c 0704 54b6
    0000050: 0020 c000 243a 0c2c 0804 5403 360d 2c10
    0000060: 0604 5419 0c15 0dba 0026 0000 aa00 0000
    0000070: 0000 00df ffff ffff 0000 0001 0000 00df
    0000080: 0000 001c 0000 006d 1905 2c10 0704 54b6
    0000090: 0027 c000 243a 0e03 360f 190e 150f ba00
    00000a0: 2600 00aa 0000 002b ffff ffff 0000 0001
    00000b0: 0000 002b 0000 0019 0000 0022 032c 1008
    00000c0: 0454 a700 9404 2c10 0904 54a7 008b 0436
    00000d0: 0d2c 100a 0454 a7ff 8d19 052c 100b 0454
    00000e0: b600 27c0 0024 3a0e 2c10 0c04 5403 360f
    00000f0: 190e 150f ba00 2600 00aa 0000 0000 0047
    0000100: ffff ffff 0000 0001 0000 0047 0000 001b
    0000110: 0000 0024 022c 100d 0454 a700 3c19 0ec0
    0000120: 0001 3a0b 2c10 0e04 5419 09b4 002a 190b
    0000130: b400 2ab9 002e 0200 2c10 0f04 54a7 0019
    0000140: 0536 0d2c 1010 0454 a7ff 1b04 3604 2c10
    0000150: 1104 54a7 fec9 2c10 1204 54ac 4ebb 001b
    0000160: 592d b600 362d b700 1d2c 1013 0454 bf
  Exception Handler Table:
    bci [75, 82] => handler: 348
    bci [138, 146] => handler: 348
    bci [219, 227] => handler: 348
  Stackmap Table:
    append_frame(@28,Object[#122],Object[#12],Integer)
    same_frame(@56)
    same_frame(@70)
    full_frame(@99,{Object[#36],Object[#36],Object[#122],Object[#12],Integer,Object[#12],Top,Top,Top,Top,Top,Top,Object[#36],Integer},{})   
    same_frame(@136)
    append_frame(@154,Object[#36],Integer)
    same_frame(@188)
    same_frame(@197)
    same_frame(@206)
    chop_frame(@217,2)
    append_frame(@240,Object[#36],Integer)
    same_frame(@276)
    same_frame(@285)
    same_frame(@320)
    chop_frame(@331,2)
    full_frame(@342,{Object[#36],Object[#36],Object[#122]},{Integer})
    same_locals_1_stack_item_frame(@348,Object[#52])

2. Workaround
The problem is at line 34:

        @Override
        default int compareTo(final Value<T> o) {
            return switch (new Tuple<>(this, o)) {
                case final Tuple<Value<T>, Value<T>>(Value.Infinite<T> _, Value.Infinite<T> _) -> 0;
                case final Tuple<Value<T>, Value<T>>(Value.Infinite<T> _, Value.Fixed<T> _) -> 1;
                case final Tuple<Value<T>, Value<T>>(Value.Fixed<T> _, Value.Infinite<T> _) -> -1;
                case final Tuple<Value<T>, Value<T>>(Value.Fixed<T> fst, Value.Fixed<T> snd) ->
                    fst.value.compareTo(snd.value);
            };
        }

By naming the first variable of the third case, everything is working

        @Override
        default int compareTo(final Value<T> o) {
            return switch (new Tuple<>(this, o)) {
                case final Tuple<Value<T>, Value<T>>(Value.Infinite<T> _, Value.Infinite<T> _) -> 0;
                case final Tuple<Value<T>, Value<T>>(Value.Infinite<T> _, Value.Fixed<T> _) -> 1;
                case final Tuple<Value<T>, Value<T>>(Value.Fixed<T> fst, Value.Infinite<T> _) -> -1;
                case final Tuple<Value<T>, Value<T>>(Value.Fixed<T> fst, Value.Fixed<T> snd) ->
                    fst.value.compareTo(snd.value);
            };
        }

[cboudereau]

openjdk issue: https://bugs.openjdk.org/browse/JDK-8317048