Re: [PATCH 2/4] merge-base: "--is-ancestor A B"

[Martin von Zweigbergk <martinvonz@gmail.com>]

(Resending as plain text, sorry about duplicate, Junio.)

On Thu, Aug 30, 2012 at 4:13 PM, Junio C Hamano <gitster@pobox.com> wrote:
>
> In many scripted Porcelain commands, we find this idiom:
>
>     if test "$(git rev-parse --verify A)" = "$(git merge-base A B)"
>     then
>         ... A is an ancestor of B ...
>     fi
>
> But you do not have to compute exact merge-base only to see if A is
> an ancestor of B.  Give them a more direct way to use the underlying
> machinery.

Thanks! It has bugged me ever since I first saw that idiom that there
was no way that better shows the intent.

> +       if (argc != 2)
> +               die("--is-ancestor takes exactly two commits");

I think git merge-base shows the usage message regardless if argc < 2,
so this only happens when more than two arguments are given. Maybe
include --is-ancestor in the usage message?

> +       if (is_ancestor && (show_all | octopus | reduce))
> +               die("--is-reachable cannot be used with other options");

I suppose --is-reachable should be --is-ancestor.