Visual C++ exception message does not print, SIGABRT instead.

[treeform]

Test code:

raise newException(IndexError, "hi there")

Correct (gcc C):

nim c -r .\bug.nim
***\bug.nim(1) bug
Error: unhandled exception: hi there [IndexError]

Correct (gcc C++):

nim cpp -r .\bug.nim
***\bug.nim(1) bug
Error: unhandled exception: hi there [IndexError]

Wrong (Visual C++)

nim cpp --cc:vcc -r .\bug.nim
***\bug.nim(1) bug
SIGABRT: Abnormal termination.

Nim version:

nim -v
Nim Compiler Version 0.20.99 [Windows: amd64]
Compiled at 2019-07-29
Copyright (c) 2006-2019 by Andreas Rumpf

active boot switches: -d:release

[mratsim]

The whole C++ backend had this issue as raised in #6512, it was fixed by c9f1844 but it seems like the fix only worked for GCC/Clang.

[treeform]

This is what I did to make it work:

setTerminate proc() {.noconv.} =
    # Remove ourself as a handler, reinstalling the default handler.
    setTerminate(nil)

    var msg = "Unknown error in unexpected exception handler"
    # try:
    #   raise
    # except Exception:
    #   msg = currException.getStackTrace() & "Error: unhandled exception: " &
    #     currException.msg & " [" & $currException.name & "]"
    # except StdException as e:
    #   msg = "Error: unhandled cpp exception: " & $e.what()
    # except:
    #   msg = "Error: unhandled unknown cpp exception"

    if currException != nil:
      msg = currException.getStackTrace() & "Error: unhandled exception: " &
        currException.msg & " [" & $currException.name & "]"

    when defined(genode):
      # stderr not available by default, use the LOG session
      echo msg
    else:
      writeToStdErr msg & "\n"

    quit 1

At

Nim/lib/system/excpt.nim

Line 486 in 572b7c3

setTerminate proc() {.noconv.} =

I think the issue is that the

try:
    raise

Just does not work with Visual C++ exceptions. But you can just look at the current exception if its there. I am not sure what this try-raise trying to do. I am confused by this.

I think this handler was made to also handle c++ native exceptions. But it was not tested on vc++.

[treeform]

Here is the issue what was being fixed by the regression: #10765 and PR 3cf0380

Hey @cooldome you worked on that PR could you take a look again maybe?

also my vc++ version:
Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24213.1 for x64

[nc-x]

Generating

try {
  std::rethrow_exception(std::current_exception());
}

instead of

try {throw;}

Works fine when tested on C++ code, but for the Nim code in this issue, msvc gives -

Error: unhandled cpp exception: bad exception

which is again wrong. (on gcc it works).

Minimal C++ code for anybody who wants to investigate

#include <exception>
#include <iostream>
using namespace std;

void x() {
  try {
    throw; // does not work in msvc
    // rethrow_exception(current_exception()); // works in msvc, but not for https://github.com/nim-lang/Nim/issues/11846
  } catch (...) {
    cout << "Called by terminate." << endl;
  }
  exit(-1);
}

int main() {
  try {
    set_terminate(x);
    throw 1;
  } catch (string) {
    cout << "ABC" << endl;
  }
  return 0;
}

[cooldome]

fixed

[treeform]

@cooldome Still not fixed for me. I get the exception stack trace but not the message. :(

[treeform]

This change here fixes it:

    {.emit"#if defined(_MSC_VER) && (_MSC_VER < 1923)".}
    #msg = "Error: unhandled unknown cpp exception"
    msg = currException.getStackTrace() & "Error: unhandled exception: " &
        currException.msg & " [" & $currException.name & "]"
    {.emit"#endif".}

[treeform]

I have updated to the newer visual VC++ and that works as well. I guess we are laving older VC++ in broken state but that's probably fine.