On Fri, Sep 13, 2019 at 10:30 PM Jeff King <peff@xxxxxxxx> wrote: > SNIP > > > Now this looks more like it. I can actually see a useful diff here, > > instead of everything looking like a new file. But there is a lot of > > confusion here: > > > > 1. `diff --follow` is not a documented[1] option. Why does it work? > > Accident. :) See above. > > > 2. `diff -M` doesn't actually work either. It should, though. In fact, > > I expected it to work as `--follow` does. But it doesn't. > > It doesn't work because this is a copy, not a rename. > > > 3. The `diff.renames` config doesn't seem to be working here, when it should. > > It does, but the pathspec prevents it from finding a source candidate. Jeff, thanks so much. All of your examples help to contrast the different behavior. I thought -M did copies & renames, that was my misunderstanding. But the fact that you explained that the file spec would prevent it from working as I'd like anyway means it doesn't matter too much. Ultimately my goal is to use the pathspec to filter what is visible, I don't necessarily intend it to obscure my results due to internal behavior. I realize there are performance obligations too (as you described) but I feel like something like this should be straightforward for end users. I consider myself a step above most people with my understanding of Git and how it functions, and even I was confused by this. Especially when it comes to folks I work with at my day job, I just don't see them making sense of this. To me, as transparently as possible, moves and copies should be handled intrinsically. I realize there are technical challenges (performance, ambiguities, etc), but anything that can be done to help with that would go a long way with most users. Maybe a 3rd option from your list to solve this issue might be adding some metadata to commits or blob object types to record the pathspec of the file it was a copy or move of. Even if this required you to first do a git cp/mv before modifying the content, or a strict similarity threshold, I think it would go a long way. That means that `diff` can utilize the metadata in the object itself to find the path specs to follow, instead of requiring some complex deduction logic that has a steep performance cost.
