Segfault when serializing class with single String field

[jtfmumm]

The following segfaults when attempting to serialize a class with a single String field.

use "serialise"

actor Main
  new create(env: Env) =>
    try
      let auth = env.root as AmbientAuth
      let psd: V = V
      Serialised(SerialiseAuth(auth), psd)?
    end

class V
  let _v: String = ""

however, with

class V
  let _v: String = "A"

it works.

[SeanTAllen]

backtrace:

* thread #2: tid = 0x4f1fa8, 0x000000010000f31c serialization-jtf`pony_serialise_offset(ctx=0x0000000108fff448, p=0x00000001000184b0) + 188 at serialise.c:213, stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x000000010000f31c serialization-jtf`pony_serialise_offset(ctx=0x0000000108fff448, p=0x00000001000184b0) + 188 at serialise.c:213
   210 	  // If we are not in the map, we are an untraced primitive. Return the type id
   211 	  // with the high bit set.
   212 	  pony_type_t* t = *(pony_type_t**)p;
-> 213 	  return (size_t)t->id | HIGH_BIT;
   214 	}
   215
   216 	PONY_API void pony_serialise(pony_ctx_t* ctx, void* p, pony_type_t* t,
(lldb) bt
warning: could not load any Objective-C class information. This will significantly reduce the quality of type information available.
* thread #2: tid = 0x4f1fa8, 0x000000010000f31c serialization-jtf`pony_serialise_offset(ctx=0x0000000108fff448, p=0x00000001000184b0) + 188 at serialise.c:213, stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: 0x000000010000f31c serialization-jtf`pony_serialise_offset(ctx=0x0000000108fff448, p=0x00000001000184b0) + 188 at serialise.c:213
    frame #1: 0x0000000100003998 serialization-jtf`String_Serialise + 88
    frame #2: 0x000000010000f4f2 serialization-jtf`pony_serialise(ctx=0x0000000108fff448, p=0x0000000108fd5860, t=0x0000000000000000, out=0x0000000108fd58a0, alloc_fn=(serialization-jtf`serialise_$2$0_apply_oZo at serialise.pony:76), throw_fn=(serialization-jtf`serialise_$2$1_apply_o at serialise.pony:79)) + 434 at serialise.c:245
    frame #3: 0x0000000100002324 serialization-jtf`serialise_Serialised_ref_create_ooo(this=0x0000000108fd5880, auth=0x00000001000223f0, data=0x0000000108fd5860) + 196 at serialise.pony:80
    frame #4: 0x00000001000016a2 serialization-jtf`Main_tag_create_oo(this=0x0000000108ffec00, env=0x0000000108ffe400) + 258 at a.pony:8
    frame #5: 0x0000000100000d55 serialization-jtf`Main_Dispatch + 117
    frame #6: 0x0000000100004269 serialization-jtf`handle_message(ctx=0x0000000108fff448, actor=0x0000000108ffec00, msg=0x0000000108fff340) + 457 at actor.c:152
    frame #7: 0x0000000100003f0b serialization-jtf`ponyint_actor_run(ctx=0x0000000108fff448, actor=0x0000000108ffec00, batch=100) + 107 at actor.c:209
    frame #8: 0x0000000100017299 serialization-jtf`run(sched=0x0000000108fff400) + 185 at scheduler.c:301
    frame #9: 0x0000000100016fa9 serialization-jtf`run_thread(arg=0x0000000108fff400) + 57 at scheduler.c:352
    frame #10: 0x00007fff97df399d libsystem_pthread.dylib`_pthread_body + 131
    frame #11: 0x00007fff97df391a libsystem_pthread.dylib`_pthread_start + 168
    frame #12: 0x00007fff97df1351 libsystem_pthread.dylib`thread_start + 13

[jtfmumm]

The String has to be empty. Updated description.

[jtfmumm]

Actually, serializing an empty string on its own segfaults.

[SeanTAllen]

This was introduced in b90ec8f

@Praetonus thoughts?