# diff --color-words breaks spacing

2 messages from 2017-01-24 to 2017-01-25. Participants: Phil Hord, Jeff King.
Thread: https://gitlist.dev/t/44960

## Phil Hord, 2017-01-24 17:39

Subject: diff --color-words breaks spacing
Message-ID: <CABURp0ryBtLALEnzRdoeYeUUdrzBxiT3+yTvW6B=vpqMG3p1Rw@mail.gmail.com>
URL: https://gitlist.dev/e/CABURp0ryBtLALEnzRdoeYeUUdrzBxiT3%2ByTvW6B%3DvpqMG3p1Rw%40mail.gmail.com

```
I noticed some weird spacing when comparing files with git diff
--color-words.  The space before a colored word disappears sometimes.

$ git --version
git version 2.11.0.485.g4e59582ff

echo "FOO foo; foo = bar" > a
echo "FOO foo = baz" > b
git diff --color-words --no-index a b
FOOfoo; foo = barbaz

There should be a space after FOO in the diff, even if git doesn't
think "foo" and "foo;" are the same word.

If I remove the semicolon, it looks better, but in fact it only moves
the error later. The missing space is now between the two "foo" words.

echo "FOO foo foo = bar" > a
echo "FOO foo = baz" > b
git diff --color-words --no-index a b
FOO foofoo = barbaz

Here's the same with the color codes changed to text for purposes of this email:

echo "FOO foo; foo = bar" > a
echo "FOO foo = baz" > b
git diff --color-words --no-index a b | tr  \\033 E
FOOE[31mfoo;E[m foo = E[31mbarE[mE[32mbazE[m

echo "FOO foo foo = bar" > a
echo "FOO foo = baz" > b
git diff --color-words --no-index a b | tr  \\033 E
FOO fooE[31mfooE[m = E[31mbarE[mE[32mbazE[m

```

## Jeff King, 2017-01-25 23:20

Subject: Re: diff --color-words breaks spacing
Message-ID: <20170125232038.bedgunhyesdytys3@sigill.intra.peff.net>
URL: https://gitlist.dev/e/20170125232038.bedgunhyesdytys3%40sigill.intra.peff.net
In-Reply-To: <CABURp0ryBtLALEnzRdoeYeUUdrzBxiT3+yTvW6B=vpqMG3p1Rw@mail.gmail.com>

```
On Tue, Jan 24, 2017 at 09:39:31AM -0800, Phil Hord wrote:

> I noticed some weird spacing when comparing files with git diff
> --color-words.  The space before a colored word disappears sometimes.

I _think_ this is working as designed, though it is a bit tricky (and it
may be possible to make it better).

> echo "FOO foo; foo = bar" > a
> echo "FOO foo = baz" > b
> git diff --color-words --no-index a b
> FOOfoo; foo = barbaz

It might be easier to see with --word-diff, which uses the same code but
marks it with punctuation:

  $ git diff --word-diff
  FOO[-foo;-] foo = [-bar-]{+baz+}

The key thing is that what you are seeing is the post-image, plus
word-based annotations. And the post-image does not have that space in
its context, so we would not expect to see:

  FOO [-foo;-] foo = [-bar-]{+baz+}

(you would if we showed the pre-image plus annotations; but then I think
you'd probably end up with the opposite problem when text was added).

However, we also don't see the space in the removed part. I.e., I think:

  FOO[- foo;-] foo = [-bar-]{+baz+}

would be correct. But I think because of the way word-diff is
implemented, a non-word character will never be part of the annotation.

The way it works is basically to break the string down on word
boundaries, so we have:

  pre: FOO, foo;, foo, =, bar
  post: FOO, foo, =, baz

as a set of tokens. We stick each of those on their own line and feed
them back to xdiff, so we get a diff like:

  @@ -1,5 +1,4 @@
   FOO
  -foo;
   foo
   =
  -bar
  +baz

and then walk through the post-image buffer, either inserting chunks of
context from the original buffer, or the changed lines. But the changed
lines themselves do not include the non-word characters, so we have no
idea that a space went away.

-Peff

```