Re: [PATCH 2/2] xdiff: implement empty line chunk heuristic

[Jacob Keller <jacob.keller@gmail.com>]

On Mon, Apr 18, 2016 at 2:12 PM, Stefan Beller <sbeller@google.com> wrote:
> In order to produce the smallest possible diff and combine several diff
> hunks together, we implement a heuristic from GNU Diff which moves diff
> hunks forward as far as possible when we find common context above and
> below a diff hunk. This sometimes produces less readable diffs when
> writing C, Shell, or other programming languages, ie:
>
> ...
>  /*
> + *
> + *
> + */
> +
> +/*
> ...
>
> instead of the more readable equivalent of
>
> ...
> +/*
> + *
> + *
> + */
> +
>  /*
> ...
>
> Implement the following heuristic to (optionally) produce the desired
> output.
>
>   If there are diff chunks which can be shifted around, shift each hunk
>   such that the last common empty line is below the chunk with the rest
>   of the context above.
>
> This heuristic appears to resolve the above example and several other
> common issues without producing significantly weird results. However, as
> with any heuristic it is not really known whether this will always be
> more optimal. Thus, it can be disabled via diff.compactionHeuristic.
>
> Signed-off-by: Stefan Beller <sbeller@google.com>
> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---

Thanks Stephan and Junio, this looks pretty good. I think before it's
merged we'd probably want to implement some sort of attributes which
allows per-path configuration, incase it needs to be configured at
all.

I've got it applied to my local git, and I'm going to try to run a
diff between enabled vs disabled on a large section of the Linux
kernel history and a few other projects to see if I spot anything odd.

Thanks,
Jake