Re: [PATCH] diff: prefer indent heuristic over compaction heuristic

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

On Thu, Dec 22, 2016 at 1:12 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Jacob Keller <jacob.keller@gmail.com> writes:
>
>> I don't think we have too many config options that interact in this
>> way, so I understand that "last writing of a particular configuration"
>> makes sense, but interactions between configs is something that would
>> have never occurred to me. I'll send a patch to drop the compaction
>> heuristic since I think we're all 100% in agreement that it is
>> superseded by the new configuration (as no case has been shown where
>> the new one is worse than compaction, and most show it to be better).
>
> If I recall correctly, we agreed that we'll drop the implementation
> of compaction, but use the name --compaction-heuristics to trigger
> the new and improved "indent heuristics":
>
>     <20161101205916.d74n6lhgp2hexpzr@sigill.intra.peff.net>
>

That sounds familiar.

> So let's do this.
>
> -- >8 --
> Subject: [PATCH] diff: retire the original experimental "compaction" heuristics
>
> This retires the experimental "compaction" heuristics but with a
> twist.  It removes the mention of "indent" heuristics, which was a
> competing experiment, from everywhere, guts the core logic of the
> original "compaction" heuristics out and replaces it with the logic
> used by the "indent" heuristics.
>
> The externally visible effect of this change is that people who have
> been experimenting by setting diff.compactionHeuristic configuration
> or giving the command line option --compaction-heuristic will start
> getting the behaviour based on the improved heuristics that used to
> be called "indent" heuristics.
>
> Suggested-by: Jeff King <peff@peff.net>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  Documentation/diff-config.txt            |  6 ++---
>  Documentation/diff-heuristic-options.txt |  2 --
>  builtin/blame.c                          |  3 +--
>  diff.c                                   | 25 ++++-----------------
>  git-add--interactive.perl                |  5 +----
>  t/t4061-diff-indent.sh                   | 38 ++++++++++++++++----------------
>  xdiff/xdiff.h                            |  1 -
>  xdiff/xdiffi.c                           | 37 +++----------------------------
>  8 files changed, 30 insertions(+), 87 deletions(-)
>
> diff --git a/Documentation/diff-config.txt b/Documentation/diff-config.txt
> index 58f4bd6afa..39fff3aef9 100644
> --- a/Documentation/diff-config.txt
> +++ b/Documentation/diff-config.txt
> @@ -171,11 +171,9 @@ diff.tool::
>
>  include::mergetools-diff.txt[]
>
> -diff.indentHeuristic::
>  diff.compactionHeuristic::
> -       Set one of these options to `true` to enable one of two
> -       experimental heuristics that shift diff hunk boundaries to
> -       make patches easier to read.
> +       Set this option to `true` to enable experimental heuristics
> +       that shift diff hunk boundaries to make patches easier to read.
>
>  diff.algorithm::
>         Choose a diff algorithm.  The variants are as follows:
> diff --git a/Documentation/diff-heuristic-options.txt b/Documentation/diff-heuristic-options.txt
> index 36cb549df9..3cb024aa22 100644
> --- a/Documentation/diff-heuristic-options.txt
> +++ b/Documentation/diff-heuristic-options.txt
> @@ -1,5 +1,3 @@
> ---indent-heuristic::
> ---no-indent-heuristic::
>  --compaction-heuristic::
>  --no-compaction-heuristic::
>         These are to help debugging and tuning experimental heuristics
> diff --git a/builtin/blame.c b/builtin/blame.c
> index 4ddfadb71f..395d4011fb 100644
> --- a/builtin/blame.c
> +++ b/builtin/blame.c
> @@ -2596,7 +2596,6 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
>                  * and are only included here to get included in the "-h"
>                  * output:
>                  */
> -               { OPTION_LOWLEVEL_CALLBACK, 0, "indent-heuristic", NULL, NULL, N_("Use an experimental indent-based heuristic to improve diffs"), PARSE_OPT_NOARG, parse_opt_unknown_cb },
>                 { OPTION_LOWLEVEL_CALLBACK, 0, "compaction-heuristic", NULL, NULL, N_("Use an experimental blank-line-based heuristic to improve diffs"), PARSE_OPT_NOARG, parse_opt_unknown_cb },
>

The unchanged context line should have its description re-worded to
something like "Use an experimental heuristic to improve diffs" as it
no longer uses only blank lines.

Everything else looked correct.

Thanks,
Jake