[jcgrillo]

That's a good point, this does seem qualitatively different. Like dialect translation. In that case the specification is really precise, it's just the old code. Building something new or adding functionality to existing software the spec is almost guaranteed to be more vague.

EDIT: this specificity seems important for language models but the harder I think about it the less sure I am that it's the right intuition..

[rincebrain]

My intuition is that what makes them well suited is that the transformations on the input desired are well-defined and frequent tasks - e.g. any other software that migrated from, say, SDL1 to SDL2, or had to move from gcc 3 to 4, or Sun cc to gcc, had to have these transformations in their source history.

IOW, "there is probably very little stopping you except time from having written Coccinelle patches to mechanically do most of these transformations".