Paper:
Learning to Repair Software Vulnerabilities with Generative Adversarial Networks
Motivated by the problem of automated repair of software vulnerabilities, we propose an adversarial learning approach that maps from one discrete source domain to another target domain without requiring paired labeled examples or source and target domains to be bijections. We demonstrate that the proposed adversarial learning approach is an effective technique for repairing software vulnerabilities, performing close to seq2seq approaches that require labeled pairs. The proposed Generative Adversarial Network approach is application-agnostic in that it can be applied to other problems similar to code repair, such as grammar correction or sentiment translation.

Review:
Update based on author rebuttal: The authors address some of my criticisms and promise to improve some of the motivation in subsequent drafts. The rebuttal doesn't change my impression of accepting this paper.  This paper proposes a system for correcting sequences, with a target application of fixing buggy source code. They use a sequence-to-sequence model within a GAN framework, which allows the model to be trained without paired source/target data. Some additional new tricks are proposed to make the model output consistent translations of the input. The model is tested on two synthetic tasks and a source code correction benchmark.  Overall, I thought this paper provided a compelling model which seems to function well on sequence-to-sequence tasks even without explicit source/target pairs. The authors focus only on datasets where explicit source/target pairs are available in order to compare their method to standard seq2seq models. This was a disappointment to me. As the authors say, "The major advantage of our approach is that it can be used in the absence of paired data, opening up a wide set of previously unusable data sets for the sequence correction task."  While the experiments suggest the model can still perform reasonably well without explicitly using the source-target pairs, the model itself was not tested in this regime. In particular, a truly realistic test of the model would be in a setting where there is no guarantee that a given source sequence has a paired target sequence anywhere in the training data. I think this paper would be a lot stronger if it was shown to work in this setting - perhaps by being deployed in a source code vulnerability detection system and proving to be genuinely useful. That being said, I am not familiar with the source code correction problem domain so I may be missing the significance of the reported results. Apart from this, I found some of the presentation confusing or otherwise amenable to improvement; some specific comments are below.   > "only a limited number of relatively small paired sequence correction datasets exist" In the context (and via the citation), it sounds like you are discussing machine translation datasets, not "sequence correction" datasets, but in that case this statement is false - there are many translation datasets, and many of them are large. From later context, I think you mean generic datasets which deal with correcting sequences (like fixing grammar errors, or source code correction), but I was thrown off by this sentence in the midst of a paragraph about MT.  - In your description of WGAN, you don't mention that in order to actually estimate Wasserstein distance the function class must be constrained to 1-Lipschitz functions, for example by weight clipping (as originally proposed in WGAN) or via a gradient penalty (as proposed by Gulrajani et al.)  You mention this later, but it's inaccurate to introduce the WGAN the way that you do without mentioning this.  - You state that you feed the discriminator "soft" network outputs directly rather than sampling. Do you still sample from the generator's output and feed the sample back in? If you don't, your model is not very powerful because it no longer has a stochastic variable and all possible future outcomes must be encoded in the deterministic hidden state. If you do, then you can't propagate gradients though the sampling operation so your model is only learning one-step dependencies. Which did you do and why? From later discussion (4.2) it sounds like the latter; I'd suggest addressing this early on.  - Your discussion of the weak discriminator feels a little incomplete to me. It is nice that with a weak discriminator you obtain useful gradients, but there is a trade-off between discriminator strength and the generator's abilities, namely because the generator only ever learns how to solve the task through the discriminator. Being able to utilize discriminator gradients is not enough - the discriminator has to be able to provide a good model of the data distribution in order to be useful. Of course, as you point out, useful gradients are a prerequisite, but my point is that the generator's performance is limited in the case of a weak generator. I would suggest adding a few sentences to comment on this.  - More common is to call the "Improved WGAN" loss the "WGAN-GP" loss, due to the gradient penalty.