  The relationship of comments to code, and in particular, the task of
generating useful comments given the code, has long been of interest. The
earliest approaches have been based on strong syntactic theories of
comment-structures, and relied on textual templates. More recently, researchers
have applied deep learning methods to this task, and specifically, trainable
generative translation models which are known to work very well for Natural
Language translation (e.g., from German to English). We carefully examine the
underlying assumption here: that the task of generating comments sufficiently
resembles the task of translating between natural languages, and so similar
models and evaluation metrics could be used. We analyze several recent
code-comment datasets for this task: CodeNN, DeepCom, FunCom, and DocString. We
compare them with WMT19, a standard dataset frequently used to train state of
the art natural language translators. We found some interesting differences
between the code-comment data and the WMT19 natural language data. Next, we
describe and conduct some studies to calibrate BLEU (which is commonly used as
a measure of comment quality). using "affinity pairs" of methods, from
different projects, in the same project, in the same class, etc; Our study
suggests that the current performance on some datasets might need to be
improved substantially. We also argue that fairly naive information retrieval
(IR) methods do well enough at this task to be considered a reasonable
baseline. Finally, we make some suggestions on how our findings might be used
in future research in this area.
