Re: [PATCH 2/3] config: Introduce diff.algorithm variable

> Some users or projects prefer different algorithms over others, e.g.
> patience over myers or similar. However, specifying appropriate
> argument every time diff is to be used is impractical. Moreover,
> creating an alias doesn't play nicely with other tools based on diff
> (git-show for instance). Hence, a configuration variable which is able
> to set specific algorithm is needed. For now, these four values are
> accepted: 'myers' (which has the same effect as not setting the config
> variable at all), 'minimal', 'patience' and 'histogram'.
>
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  Documentation/diff-config.txt          | 17 +++++++++++++++++
>  contrib/completion/git-completion.bash |  1 +
>  diff.c                                 | 23 +++++++++++++++++++++++
>  3 files changed, 41 insertions(+)
>
> diff --git a/Documentation/diff-config.txt b/Documentation/diff-config.txt
> index 4314ad0..be31276 100644
> --- a/Documentation/diff-config.txt
> +++ b/Documentation/diff-config.txt
> @@ -155,3 +155,20 @@ diff.tool::
>  	"kompare".  Any other value is treated as a custom diff tool,
>  	and there must be a corresponding `difftool.<tool>.cmd`
>  	option.
> +
> +diff.algorithm::
> +	Choose a diff algorithm.  The variants are as follows:
> ++
> +--
> +`myers`;;
> +	The basic greedy diff algorithm.
> +`minimal`;;
> +	Spend extra time to make sure the smallest possible diff is
> +	produced.
> +`patience`;;
> +	Use "patience diff" algorithm when generating patches.
> +`histogram`;;
> +	This algorithm extends the patience algorithm to "support
> +	low-occurrence common elements".
> +--
> ++

> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
> index 383518c..33e25dc 100644
> --- a/contrib/completion/git-completion.bash
> +++ b/contrib/completion/git-completion.bash
> @@ -1839,6 +1839,7 @@ _git_config ()
>  		diff.suppressBlankEmpty
>  		diff.tool
>  		diff.wordRegex
> +		diff.algorithm
>  		difftool.
>  		difftool.prompt
>  		fetch.recurseSubmodules
> diff --git a/diff.c b/diff.c
> index 732d4c2..ddae5c4 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -36,6 +36,7 @@ static int diff_no_prefix;
>  static int diff_stat_graph_width;
>  static int diff_dirstat_permille_default = 30;
>  static struct diff_options default_diff_options;
> +static long diff_algorithm = 0;

>  static char diff_colors[][COLOR_MAXLEN] = {
>  	GIT_COLOR_RESET,
> @@ -143,6 +144,20 @@ static int git_config_rename(const char *var, const char *value)
>  	return git_config_bool(var,value) ? DIFF_DETECT_RENAME : 0;
>  }
>  
> +static long parse_algorithm_value(const char *value)
> +{
> +	if (!value || !strcasecmp(value, "myers"))
> +		return 0;
> +	else if (!strcasecmp(value, "minimal"))
> +		return XDF_NEED_MINIMAL;
> +	else if (!strcasecmp(value, "patience"))
> +		return XDF_PATIENCE_DIFF;
> +	else if (!strcasecmp(value, "histogram"))
> +		return XDF_HISTOGRAM_DIFF;
> +	else
> +		return -1;
> +}
> +
>  /*
>   * These are to give UI layer defaults.
>   * The core-level commands such as git-diff-files should
> @@ -196,6 +211,13 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
>  		return 0;
>  	}
>  
> +	if (!strcmp(var, "diff.algorithm")) {
> +		diff_algorithm = parse_algorithm_value(value);
> +		if (diff_algorithm < 0)
> +			return -1;
> +		return 0;
> +	}
> +
>  	if (git_color_config(var, value, cb) < 0)
>  		return -1;
>  
> @@ -3213,6 +3235,7 @@ void diff_setup(struct diff_options *options)
>  	options->add_remove = diff_addremove;
>  	options->use_color = diff_use_color_default;
>  	options->detect_rename = diff_detect_rename_default;
> +	options->xdl_opts |= diff_algorithm;
>  
>  	if (diff_no_prefix) {
>  		options->a_prefix = options->b_prefix = "";