Re: bug: transform a binary file into a symlink in one commit => invalid binary patch

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Fri, Jan 23, 2009 at 01:25:30PM +0100, Pixel wrote:
>
>> i hit a bug (git 1.6.1): when you transform a binary file into a
>> symlink in one commit, the binary patch can't be used in "git apply".
>> Is it a known issue?
>
> Not that I know of.
>
> Below is a patch against the test suite that fairly neatly displays the
> problem. I didn't get a chance to look into actually fixing it, though
> (I'm not even sure the problem is in apply, and not in the generated
> patch).

The generated diff is wrong.

A filepair that changes type must be split into deletion followed by
creation, which means the "index" line should say 0{40} on the right hand
side for the first half and then 0{40} on the left hand side for the
second half.  The patch generated by this step:

> +test_expect_success 'create patch' '
> +	git diff-tree --binary HEAD^ HEAD >patch
> +'

However says the blob contents change from "\0" to "file" on both.

This is because diff.c::run_diff() computes "index" only once and reuses
it for both halves.