Re: Rename handling

Johannes Schindelin wrote:

I completely understand the arguments in favor of automatic renaming. I have never once advocated getting rid of it. It is useful and valuable and works well within its constraints.

For some reason whenever I try to argue that we need, IN ADDITION to the automatic rename detection, a way to provide hints to the merge engine that a non-auto-detectable rename has occurred, the responses I get back are mostly of the form, "But the automatic rename detection handles all these cases that wouldn't be handled with manual rename marking!" It's as if one can either think autodetection is a good idea, or manual flagging is a good idea, but under no circumstances could they both be good ideas at the same time. (As evidenced by the comment above about "someone who previously thought manual renames were a pretty clever thing.") But they are not in fact mutually exclusive.

Say you're tracking a directory full of video files. Even a slight tweak to one of them (to put a logo in the corner, say, while moving it into an "accessible by the public" directory) will result in a file that has no content in common at all if you look at it as purely a stream of bytes. Short of decoding the thing to video frames and looking for similarities in the images, there's no way any merge tool will ever be able to tell the two versions are the same file unless the user indicates it. Any tool that saves its files in compressed form will have a similar problem: unless git knows how to uncompress the tool's files, a content comparison will often be useless to detect similarities.

Of course, git actually does give you a way to mark renames manually: commit them by themselves without changing the content. The problem is that that overloads the "record this snapshot of the tree for posterity" command purely for the purpose of working around the merge tool's inability to detect the rename. If other people are like me, when they record a rename-only commit immediately followed by a content-change commit on the same files, the intermediate state of the tree (with just the renames) is not actually an interesting point in the history of the project. It's not a revision in anything but an internal git sense. It probably doesn't even compile or work correctly. It exists only because I'm forced to create it if I want to be 100% certain my renames will be tracked accurately. It is, in short, pollution in the history of my project.

It also means that if I want reliable renames, I can no longer impose the requirement that my project be in a buildable state at each commit. That doesn't seem like all that unreasonable a thing to want (but maybe it is?) -- I don't want to be in the situation where I say, e.g. "git checkout -b testbranch '@{1 day ago}'" and get a broken working copy because I happened to do it at just the wrong time of day. But with the "just commit your renames separately" approach, that's exactly what can happen.

Now, once again, none of the above is an argument against the automatic rename detection. For cases where renames are automatically detectable, it works fine and will continue to do so, and in fact doesn't have the problem of committing broken builds. I am not arguing it should be replaced or that the user should be required to tell git about every rename. But the lack of an additional manual option forces me into a particular workflow that I wouldn't otherwise use and prevents me from imposing the workflow rules I *do* want.

Hopefully that shed a little light on why I think manual rename support is not a totally idiotic idea.

-Steve