Re: [Question] Diff text filters and git add

From: Jeff King <peff@peff.net>
Date: Jul 9, 2019, 21:51 UTC
Message-ID: <20190709215104.GA20936@sigill.intra.peff.net>
In-Reply-To: <009201d5369f$4da5d030$e8f17090$@nexbridge.com>

On Tue, Jul 09, 2019 at 05:43:05PM -0400, Randall S. Becker wrote:

Show 8 quoted lines

> I am trying to do something a bit strange and wonder about the best way to
> go. I have a text filter that presents content of very special binary file
> formats using textconv. What I am wondering is whether using the textconv
> mechanism is sufficient to have git calculate the file signature or whether
> I need to use an external diff engine, so that git add behaves in a stable
> manner (i.e., does git internally use the textconv mechanism for evaluating
> whether a file changed or whether the external diff engine is required, or
> whether this is even possible at all).

No, textconv only applies when generating a diff to output, and will never impact what's stored in Git.

It sounds like you might want a clean filter instead, to sanitize the file contents as they come into Git (and perhaps a matching smudge filter to convert back to the working-tree version if necessary).

You're talking about "the diff engine" here, but note that git-add would never do a diff at all. It cares only about full sha1s (and optimizes out re-computing the sha1 on each invocation by using stat data). So outside of clean/smudge, there's nothing else going on.

-Peff