Michal Privoznik <mpriv...@redhat.com> writes:

> +--diff-algorithm={patience|minimal|histogram|myers}::
> +     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".
> +--
> ++
> +For instance, if you configured diff.algorithm variable to a
> +non-default value and want to use the default one, then you
> +have to use `--diff-algorithm=myers` option.
> +
> +You should prefer this option over the `--minimal`, `--patience` and
> +`--histogram` which are kept just for backwards compatibility.

Much better; I'd drop the last paragraph, though.

I also think we really should consider "default" synonym for
whichever happens to be the built-in default (currently myers).

> diff --git a/diff.c b/diff.c
> index e9a7e4d..3e021d5 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -144,7 +144,7 @@ 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)
> +long parse_algorithm_value(const char *value)
>  {
>       if (!value || !strcasecmp(value, "myers"))
>               return 0;
> @@ -3633,6 +3633,16 @@ int diff_opt_parse(struct diff_options *options, const 
> char **av, int ac)
>               options->xdl_opts = DIFF_WITH_ALG(options, PATIENCE_DIFF);
>       else if (!strcmp(arg, "--histogram"))
>               options->xdl_opts = DIFF_WITH_ALG(options, HISTOGRAM_DIFF);
> +     else if (!prefixcmp(arg, "--diff-algorithm=")) {
> +             long value = parse_algorithm_value(arg+17);
> +             if (value < 0)
> +                     return error("option diff-algorithm accepts \"myers\", "
> +                                  "\"minimal\", \"patience\" and 
> \"histogram\"");
> +             /* clear out previous settings */
> +             DIFF_XDL_CLR(options, NEED_MINIMAL);
> +             options->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
> +             options->xdl_opts |= value;

This makes me wonder if other places that use DIFF_WITH_ALG() also
need to worry about clearing NEED_MINIMAL?

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