From: Garthy D <garthy_lmkltybr@...>
Date: 2013-02-25T13:59:25+09:00
Subject: 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