flx_args is overwritten while parsing #23

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1. Winand

   changed the title [-]`flx_args` variable is overwritten while parsing[/-] [+]`flx_args` is overwritten while parsing[/+] on May 7, 2018
2. almarklein

   added

   bugSomething isn't workingSomething isn't working

   on May 14, 2018
3. almarklein commented on Oct 5, 2018

   

   almarklein

   on Oct 5, 2018

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   I am sorry, but I am having trouble understanding the problem. I don't see how fle_args[0] is overwritten; it is only indexed, right?

   I tried to work with the example in your PR:

   from pscript import py2js, evaljs
   
   def partial2(a1, a2, *args, **kwargs):
       print(a1, a2)
       print(args)
       print(kwargs)
       print('--')
   
   def main():
       partial2(3, 4, 5, 6, foo=3, bar=4)
   
   js = py2js(partial2)
   # print(js)
   print(evaljs(js + py2js(main) + 'main(); partial2(3, 4, 5)'))

   Which produces this, which seems fine:

   3 4
   [ 5, 6 ]
   { foo: 3, bar: 4 }
   --
   3 4
   [ 5 ]
   {}
   --
   null
   

   Could you please try to adjust this code for it to cause the error on your end? That would hopefully make things more explicit :)
4. Winand commented on Oct 5, 2018

   

   Winand

   on Oct 5, 2018

   ContributorAuthor

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   Ok, I created a file test.py:

   def partial2(a1, a2, *args, **kwargs):
       print(a1, a2)
       print(args)
       print(kwargs)
       print('--')
   
   def main():
       partial2(3, 4, 5, 6, foo=3, bar=4)
   
   main()
   partial2(3, 4, 5)
   

   Then I compiled it to test.js with script2js:

   /* Do not edit, autogenerated by pscript */
   
   var _pyfunc_op_error = function (etype, msg) { // nargs: 2
       var e = new Error(etype + ': ' + msg);
       e.name = etype
       return e;
   };
   var _pyfunc_op_parse_kwargs = function (arg_names, arg_values, kwargs, strict) { // nargs: 3
       for (var i=0; i<arg_values.length; i++) {
           var name = arg_names[i];
           if (kwargs[name] !== undefined) {
               arg_values[i] = kwargs[name];
               delete kwargs[name];
           }
       }
       if (strict && Object.keys(kwargs).length > 0) {
           throw _pyfunc_op_error('TypeError',
               'Function ' + strict + ' does not accept **kwargs.');
       }
       return kwargs;
   };
   var main, partial2;
   partial2 = function flx_partial2 (a1, a2) {
       var args, kwargs, stub1_args;
       kwargs = {};
       if (arguments.length == 1 && typeof arguments[0] == 'object' && Object.keys(arguments[0]).toString() == 'flx_args,flx_kwargs') {
           kwargs = _pyfunc_op_parse_kwargs([], [], arguments[0].flx_kwargs);
           stub1_args = arguments[0].flx_args;
           a1 = stub1_args[0];
           a2 = stub1_args[1];
           args = arguments[0].flx_args.slice(2);
       } else {args = Array.prototype.slice.call(arguments, 2);}
       console.log(a1 + " " + a2);
       console.log(args);
       console.log(kwargs);
       console.log("--");
       return null;
   };
   
   main = function flx_main () {
       partial2({flx_args: [3, 4, 5, 6], flx_kwargs: {foo: 3, bar: 4}});
       return null;
   };
   
   main();
   partial2(3, 4, 5);
   

   When running this script in Chrome 70 I get the following error:
   

   How is it possible?
   I couldn't believe it but when we assign a1 = stub1_args[0]; we assign 3 to arguments[0] 😞
   
5. almarklein commented on Oct 5, 2018

   

   almarklein

   on Oct 5, 2018

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   Wow! This is madness ... but I can confirm it on both Chrome and Firefox (Windows 10). It looks like a1 is somehow bound to the same spot in memory as argumens[0], but that's not how variables are supposed to work, right? Is this some obscure result of the browser's JS optimization?

   JS is full of surprises :(
6. almarklein commented on Oct 5, 2018

   

   almarklein

   on Oct 5, 2018

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   https://spin.atomicobject.com/2011/04/10/javascript-don-t-reassign-your-function-arguments/