[PATCH 0/3] fixing "diff --relative" with external diff

From: Jeff King <peff@peff.net>
Date: Jan 6, 2023, 11:00 UTC
Message-ID: <Y7f/YiVu1TgbucDI@coredump.intra.peff.net>
In-Reply-To: <CALiLy7raQsK3j+f6+dpYrEiegvFZRra5F9JwPWu---4h_AR49w@mail.gmail.com>

On Wed, Jan 04, 2023 at 03:03:17PM -0700, Carl Baldwin wrote:

Show 9 quoted lines

> What did you expect to happen? (Expected behavior)
> 
>     When using a diff.external command with --relative, the diff output should
>     show the minor change that I made to the file.
> 
> What happened instead? (Actual behavior)
> 
>     The diff output shows the entire old contents of the file as deleted. The
>     header of the patch looked like this (indent added for this report):

Nice catch, and thank you for a clear reproduction recipe. It looks like this bug has been lurking since --relative was introduced in 2008. :)

Here's a patch series which fixes it. The first one is the fix itself, and the other two are some cleanups we can do on top (I almost squashed them in, but their diffs are rather noisy and make it harder to see the actual fix).

  [1/3]: diff: use filespec path to set up tempfiles for ext-diff
  [2/3]: diff: clean up external-diff argv setup
  [3/3]: diff: drop "name" parameter from prepare_temp_file()

 diff.c                   | 30 +++++++++++++-----------------
 t/t4045-diff-relative.sh | 29 +++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 17 deletions(-)

-Peff