Re: [PATCH] merge-recursive: fix the diff3 common ancestor label for virtual commits

>
> In commit 743474cbfa8b ("merge-recursive: provide a better label for
> diff3 common ancestor", 2019-08-17), the label for the common ancestor
> was changed from always being
>
>          "merged common ancestors"
>
> to instead be based on the number of merge bases:
>
>     >=2: "merged common ancestors"
>       1: <abbreviated commit hash>
>       0: "<empty tree>"
>
> Unfortunately, this did not take into account that when we have a single
> merge base, that merge base could be fake or constructed.  In such
> cases, this resulted in a label of "00000000".  Of course, the previous
> label of "merged common ancestors" was also misleading for these cases.
> Since we have an API that is explicitly about creating fake commits in
> merge_recursive_generic(), we should provide a better label when using
> that API.  So, when merge_recursive_generic() is called, set the label
> to:
>
>          "constructed merge base"
>
> Note that users of merge_recursive_generic include the builtin commands
> git-am (in combination with git apply --build-fake-ancestor),
> git-merge-recursive, and git-stash.
>
> Reported-by: Jeff King <peff@peff.net>

> @@ -3741,6 +3744,7 @@ int merge_recursive_generic(struct merge_options *opt,
>                                            oid_to_hex(merge_bases[i]));
>                         commit_list_insert(base, &ca);
>                 }
> +               opt->ancestor = "constructed merge base";