Fix SyntaxError due to function declarations

[christofferqa]

See #107.

[msridhar]

@christofferqa can you also add a regression test for this issue?

[christofferqa]

@msridhar Added a test case that fails with the current master branch:

christofferqa:jalangi2 cqa$ python scripts/test.analysis.py 
es2015_syntax failed

analysis exception!!!
/jalangi2/tests/unit/es2015_syntax_jalangi_.js:23
            var f = J$.X1(41, J$.W(33, 'f', J$.T(25, 42, 22, false), f, 3));
                                                                          ^
SyntaxError: Identifier 'f' has already been declared
    at Object.exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:513:28)
    at Object.Module._extensions..js (module.js:550:10)
    at Module.load (module.js:458:32)
    at tryModuleLoad (module.js:417:12)
    at Function.Module._load (module.js:409:3)
    at Function.Module.runMain (module.js:575:10)
    at startProgram (/jalangi2/src/js/commands/direct.js:70:13)
    at MyAnalysis.onReady (/jalangi2/src/js/runtime/analysisCallbackTemplate.js:638:13)
    at ChainedAnalyses.self.(anonymous function) [as onReady] (/jalangi2/src/js/sample_analyses/ChainedAnalyses.js:65:59)

[ksen007]

what is es2015?

[christofferqa]

ECMAScript 2015. I added the test case to show that the current version of Jalangi throws a SyntaxError for code that is not syntactically correct itself (the instrumented program is, though).

I have come across this issue after using Jalangi to instrument some of the most popular libraries for web applications.

[ksen007]

Jalangi only supports ES5. It cannot handle any later version.

On Nov 22, 2016, at 11:44 PM, christofferqa notifications@github.com wrote:

ECMAScript 2015. I added the test case to show that the current version of Jalangi throws a SyntaxError for code that is not syntactically correct itself (the instrumented program is, though).

I have come across this issue after using Jalangi to instrument some of the most popular libraries for web applications.

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[msridhar]

@ksen007 reading #107 I think the issue is that Jalangi-instrumented code that might have worked in previous browser versions no longer works, due to changes in the browsers related to ES2015. @christofferqa is that right?

[christofferqa]

@msridhar Yes, that is the case. Since the browsers are now implementing ES2015, Jalangi introduces a SyntaxError on certain code.
@ksen007 This is not a matter of extending Jalangi to handle new syntactic JavaScript constructs -- it is merely a matter of adjusting the instrumentation such that it does not introduce a SyntaxError.

Try to instrument this simple program using Jalangi, and run the instrumented program in Chrome:

function inc() {}
var inc = function (i) {
  return i+1;
};

[floledermann]

This patch breaks functions that redefine themselves. Simple test case:

function _test() {
  _test = function() {
    return "A";
  }
  return _test();
}
var result = _test();

With your patch applied, this sends Jalangi off into an infinite loop (since _test is never redefined)

While this may seem like an obscure testcase, is is perfectly valid syntax and unfortunately used e.g. by babel to polyfill the typeof operator.

[floledermann]

This is really weird and I do not fully understand it, but it seems that modern JS engines have trouble redefining named functions. I am not set up to provide a formal patch to your PR, but if I remove assigning a name to the generated function (var _test = function **_test** { ... }) (lines 1829 and 1832 in your patch of esnstrument.js) then the testcase given above runs correctly after instrumentation.

I guess assigning a name to the function literal is not really necessary, at least my tests all run correctly after the change.