John Keeping wrote:

> The "diff-algorithm" option to the recursive merge strategy takes the
> name of the algorithm as an option, but it uses strcmp on the option
> string to check if it starts with "diff-algorithm=", meaning that this
> options cannot actually be used.
> Fix this by switching to prefixcmp.  At the same time, clarify the
> following line by using strlen instead of a hard-coded length, which
> also makes it consistent with nearby code.
> Reported-by: Luke Noel-Storr <>
> Signed-off-by: John Keeping <>

Thanks, both.

> --- a/merge-recursive.c
> +++ b/merge-recursive.c
> @@ -2069,8 +2069,8 @@ int parse_merge_opt(struct merge_options *o, const char 
> *s)
>               o->xdl_opts = DIFF_WITH_ALG(o, PATIENCE_DIFF);
>       else if (!strcmp(s, "histogram"))
>               o->xdl_opts = DIFF_WITH_ALG(o, HISTOGRAM_DIFF);
> -     else if (!strcmp(s, "diff-algorithm=")) {
> -             long value = parse_algorithm_value(s+15);
> +     else if (!prefixcmp(s, "diff-algorithm=")) {
> +             long value = parse_algorithm_value(s + 
> strlen("diff-algorithm="));
>               if (value < 0)
>                       return -1;

While we're here:

Part of the problem is that there are no tests for this option (or for
'git diff --diff-algorithm', or for the '[diff] algorithm'
configuration), so we didn't notice it didn't work until someone
actually tried it.

Do you have any examples of a diff or merge that works better with
some particular diff algorithm, that could be used in tests?

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