Forum: Ruby Possible mruby bug in mrb_load_string

Hi all,

I have been having a bit of a play around with mruby (note: mruby, not
MRI Ruby), and I believe I may have found a bug in a recent (20120222)
version.

Basically, if you call mrb_load_string with something that returns a
class, then make a call on the returned object that throws an exception,
and then call mrb_load_string with a string that makes the same kind of
return, the class in question has somehow vanished from the environment,
and the second load will fail.

Test program and Makefile below. The test string is simply "Float",
which returns the Float class. The first time it calls it, it is okay.
The second time, "Float" no longer exists.

Naturally, if you remove the call to 'dummyCall', the second load works
as it should.

I have seen the problem with other classes as well, although the
specifics of what triggers the problem can vary. It is hard to make a
general statement as to the exact fault. As a general rule, if any Class
is returned from mrb_load_string, and a subsequent call on the return
generates an exception, depending on what you do, the whole Class may or
may not (seem to) be removed from the current environment.

I was wondering if anyone familiar with mruby would be happy to skim
over my code below and let me know of any mistakes I may have made, and
possibly test out the code with their version of mruby, to see if it
works or fails for them as well. I want to make sure I haven't made a
mistake myself before I report it as a bug in mruby. I hope at least one
person here is using or has used mruby. :}

I am using mruby as checked out on 20120222, Linux, 64-bit.

Cheers,
Garth

-----------------
floatnom.c
-----------------

#include <mruby.h>
#include <mruby/compile.h>
#include <mruby/string.h>
#include <assert.h>
#include <string.h>

static void show_result(mrb_state *mrb, mrb_value v)
{
   switch (mrb_type(v))
   {
     case MRB_TT_CLASS:
       fprintf(stderr, "- Type Class returned.\n");
       break;
     case MRB_TT_FALSE:
       fprintf(stderr, "- Type false/nil returned.\n");
       break;
     default:
       fprintf(stderr, "- Type %d returned.\n", mrb_type(v));
       break;
   }

   if (mrb->exc)
   {
     struct RObject *exc = mrb->exc;
     mrb->exc = 0;
     mrb_value e = mrb_obj_value(exc);
     mrb_value e_to_s = mrb_funcall(mrb, e, "to_s", 0);
     assert(mrb->exc == 0);
     if (mrb_type(e_to_s) == MRB_TT_STRING)
     {
       char buff[512];
       memcpy(buff, RSTRING_PTR(e_to_s), RSTRING_LEN(e_to_s));
       buff[RSTRING_LEN(e_to_s)] = '\0';
       fprintf(stderr, "- Exception was: %s\n", buff);
     }
     else
       fprintf(stderr, "- Exception could not be identified.\n");
     assert(mrb->exc == 0);
   }
   else
     fprintf(stderr, "- No exception.\n");
}

int main(int argc, char *argv[])
{
   mrb_state *mrb = mrb_open();

   fprintf(stderr, "Loading first string:\n");
   mrb_value v1 = mrb_load_string(mrb, "Float");
   show_result(mrb, v1);

   fprintf(stderr, "Making bad call:\n");
   mrb_value v2 = mrb_funcall(mrb, v1, "dummyCall", 0);
   show_result(mrb, v2);

   fprintf(stderr, "Loading same string again. Should work, but
doesn't.\n");
   mrb_value v3 = mrb_load_string(mrb, "Float");
   show_result(mrb, v3);

   mrb_close(mrb);
   return 0;
}

-----------------
Makefile
-----------------

floatnom: floatnom.o
  gcc -o floatnom floatnom.o -L/path/to/mruby/lib -lmruby -lm

floatnom.o: floatnom.c
  gcc -Wall -o floatnom.o -I/path/to/mruby/include -c floatnom.c

clean:
  rm -f floatnom floatnom.o


-----------------
Typical output
-----------------

(May be typos- transcribed by hand)

Loading first string:
- Type Class returned.
- No exception.
Making bad call:
- Type false/nil returned.
- Exception was: undefined method 'dummyCall' for Float
Loading same string again. Should work, but doesn't.
- Type false/nil returned.
- Exception was: uninitialized constant Float

Hi all,

Whoops, I mean 20130222 rather than 20120222. About 3 days ago, not one
year and three days. I'm still mentally stuck in 2012 I think. ;)

Cheers,
Garth

On Feb 24, 2013, at 20:59 , Garthy D 
<garthy_lmkltybr@entropicsoftware.com> wrote:

>
> Hi all,
>
> I have been having a bit of a play around with mruby (note: mruby, not MRI 
Ruby), and I believe I may have found a bug in a recent (20120222) version.

Please resend this (with your followup corrections) to ruby-core@ or 
directly to bugs.ruby-lang.org

Hi Ryan,

Thanks for the suggestion. I've been meaning to sign up to ruby-core,
this sounds like the perfect excuse to do so.

Cheers,
Garth

Hi,

ruby-core is for CRuby specific or Ruby in general.  Use github issues
at <github.com/mruby/mruby> for mruby.

In message "Re: Possible mruby bug in mrb_load_string"
    on Tue, 26 Feb 2013 16:12:08 +0900, Garthy D 
<garthy_lmkltybr@entropicsoftware.com> writes:

|Hi Ryan,
|
|Thanks for the suggestion. I've been meaning to sign up to ruby-core,
|this sounds like the perfect excuse to do so.
|
|Cheers,
|Garth

Hi Matz,

Thanks for letting me know. I've put the post in as an issue for mruby
at github:

https://github.com/mruby/mruby/issues/894

Cheers,
Garth

Yukihiro Matsumoto <matz@ruby.or.jp> wrote:
> Hi,
>
> ruby-core is for CRuby specific or Ruby in general.  Use github issues
> at <github.com/mruby/mruby> for mruby.

When will there be a mailing list for mruby?

I'm not comfortable with GitHub.  It's not Free Software and
it's design encourages reliance on GH-specific tools/interaction.
I realize I am a minority here, though.

Hi,

In message "Re: Possible mruby bug in mrb_load_string"
    on Tue, 26 Feb 2013 17:46:37 +0900, Eric Wong 
<normalperson@yhbt.net> writes:

|When will there be a mailing list for mruby?
|
|I'm not comfortable with GitHub.  It's not Free Software and
|it's design encourages reliance on GH-specific tools/interaction.
|I realize I am a minority here, though.

I have no plan for a mailing list now, since I am not capable to
handle even more mails, although I understand your concern.

              matz.