nim cpp -r --gc:arc segfaults on caught AssertionError

[timotheecour]

nim cpp -r --gc:arc segfaults on dereferencing e in Exception as e

Example

when true:
  type MyExcept = object of CatchableError
  proc gun()=
    raise newException(MyExcept, "some msg")
  proc fun()=
    try:
      gun()
    except Exception as e:
      echo "caught1"
      echo ("caught2", e.msg, e.name) # segfault here for `nim cpp --gc:arc`
  fun()

Current Output

nim cpp -r --gc:arc main.nim

caught1
("caught2", "some msg", "MyExcept")
Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(75) t0900
/Users/timothee/git_clone/nim/Nim_prs/lib/system/excpt.nim(73) fun
/Users/timothee/git_clone/nim/Nim_prs/lib/system/refs_v2.nim(116) nimDestroyAndDispose
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

Expected Output

caught1
("caught2", "some msg", "MyExcept")

Additional Information

• devel 5e9ebe9
• see also nim c --gc:arc --exceptions:{setjmp,goto} incorrectly handles raise; nim cpp --gc:arc is ok #13070
• nim c --gc:arc --exceptions:goto doesn't crash but gives:

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(63) t0900
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(60) fun
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(57) gun
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(27) failedAssertImpl
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(20) raiseAssert
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(45) sysFatal
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(33) sysFatal
Error: unhandled exception: /Users/timothee/git_clone/nim/timn/tests/nim/all/t0900.nim(57, 14) `false` threw.. [AssertionError]

this is NOT discussed in this issue

[c-blake]

I was able to reproduce this with nim-9fc04a555ca0fc9eaff6d4eb9ba47a0a64feb9c2 compiled with and compling client code with gcc-8.3.0 on Linux with no user nim.cfg and only --exceptions:goto and this code:

proc doIt() =
  raise newException(CatchableError, "")
try:
  doIt()
except:
  quit(1)

Putting the try/except in a main() and calling it does not help. Catching except CatchableError: ... or except CatchableError as e: .. also changes nothing. Changing from the default gc to --gc:arc also changes nothing. The exception is not caught in any of those cases. Changing CatchableError to Exception changes nothing, but I guess the intent is for that to fail in exactly this way.

This all seemed really basic. So, I went to tests/exceptions/. Many of those seem to compile and work, but perhaps the most relevant nim c --exceptions:goto tests/exception/texceptions.nim fails to Nim-compile with the exception in expression, saying texceptions.nim(72, 7) Error: expression '1' is of type 'int literal(1)' and has to be discarded. That compiles in other --exception modes and I suspect is a known problem being in tests/.

Commenting out said block makes tests/exception/texceptions.nim compile and then also reproduce this problem in my environment. The first uncaught-that-should-be-caught one that I see is the ValueError raised in fun1. Perhaps @timotheecour can confirm for his environment or @Araq for Windows? I have not yet tried to dig into the generated C code.

[Araq]

@c-blake Your bug has been fixed, but the original bug with nim cpp remains so I'm leaving this open until my C++ exception handling bugfixes are ready.

[c-blake]

Cool. Yeah, bug seems squashed to me. Thanks for the rapid response and good luck with the cpp target.