From: Jeff King <peff@peff.net>
Date: Tue, 20 Mar 2018 15:58:14 GMT
Subject: Re: [BUG] log --graph corrupts patch
Message-ID: <20180320155814.GA32366@sigill.intra.peff.net>
In-Reply-To: <1e686ea0-90ac-f3f4-7bcf-6951c9253598@talktalk.net>

On Tue, Mar 20, 2018 at 09:58:14AM +0000, Phillip Wood wrote:

> > Are you using any exotic filters for your pager? If you use "git
> > --no-pager" does the problem persist?
> 
> Hi Peff, thanks for taking the time to check this, I had forgotten about
> the pager. I'm using diff-highlight and it seems that is causing the
> problems.

Heh. Lucky guess. Unsurprisingly, I use diff-highlight, too. But I did
not see it because I never bothered to upgrade my personal copy of the
script, which has been working for me for ages, to the one in contrib/.

But indeed, I can easily reproduce the problem with that version of the
script. Here's a pretty minimal reproduction:

-- >8 --

cat >bad <<\EOF
* commit whatever
| other stuff irrelevant
|
| diff --git a/foo b/foo
| --- a/foo
| --- b/foo
| @@ -100,6 +100,9
|  some
|  context
|  lines
| +some
| +new
| +lines
|  -context line with a leading minus
|  and other
|  context
EOF

contrib/diff-highlight/diff-highlight <bad

-- 8< --

which produce:

...
|  -context line with a leading minus
| +some
| +new
| +lines
...

The issue bisects to 7e4ffb4c17 (diff-highlight: add support for --graph
output, 2016-08-29). I think the problem is the "\s+" at the end of the
$GRAPH regex, which soaks up the space for the context, and accidentally
treats the "-" line as a preimage removal.

But just switching that to "\s" doesn't quite work. We may have an
arbitrary number of spaces between the graph ascii-art and the diff.
E.g., if you have a commit at the base of a branch (the test in
contrib/diff-highlight shows this case).

So I think you'd have to record the indent of the previous hunk header,
and then make sure that the indent matched that. But even there, I think
we're subject to false positives if a commit message contains a hunk
header (it's indented an extra 4 characters, but we'd accidentally soak
that up thinking it was graph indentation).

To make it bullet-proof, I think we'd have to actually parse the graph
structure, finding a "*" line and then accepting only an indent that
matched it.

-Peff