Re: Tracking file metadata in git -- fix metastore or enhance git?

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Apr 10, 2011, 00:15 UTC
Message-ID: <20110410001518.GA6380@elie>
In-Reply-To: <BANLkTim5DPjGjJ=SfnNfXpzCd6=PKnSs6g@mail.gmail.com>

Hi again.

Chris Webb wrote:

> (Disclaimer: I've never tried using smudge filters; maybe they can't be used
> in the way I describe!)

In the current form, they couldn't. smudge/clean filters take their input through stdin and write their output to stdout --- there is not a chance to look at the on-disk directory entry to get metadata.

It might be possible to introduce a new %p substitution pointing to the actual file the filter is working on, since with a few exceptions, the file passed to a clean filter is already on-disk. Exceptions:

 * "git blame --contents=- -- <path>" reads from stdin instead of <path>.

 * the low-level --renormalize facility (see git-merge(1)) and its
   callers feed a clean filter with output from a smudge filter before
   content hits the disk.

 * "git hash-object --path=<path> --stdin" reads from stdin instead of
   <path>.

I'd be worried about using a clean filter to store timestamps. Treating a file as changed whenever mtime changes could be confusing. Treating atime changes as content changes would be even stranger.

Richard Hartmann wrote:

> One large question in my mind is if anyone who's familiar enough with
> the codebase and has the time would be interested in actually
> implementing this.

I don't think this has to touch git core, except perhaps as mentioned above. Please feel free to cc me if working on hooks (pre-commit hook or clean filter) to automatically track metadata and some mechanism to restore it. I'd be glad to give feedback and help in any other way I can.

To be clear, I will not be driving this forward --- it's just not something I've ever needed, so I'd trust others to do a better job of taking good care of the actual use cases.

Ciao, Jonathan