Re: [PATCH v6 2/3] graph: add support for --line-prefix on all graph-aware output

Jacob Keller [off-list ref] writes:

To make this work, we have to fix a few bugs in the graph API that force
graph_show_commit_msg to be used only when you have a valid graph.
Additionally, we extend the default_diff_output_prefix handler to work
even when no graph is enabled.

This is somewhat of a hack on top of the graph API, but I think it
should be acceptable here.

Unlike the opt-prefix-length I removed in 1/3, the length of the
line-prefix will never change during the lifetime of a single
diff_options struct, so it might turn out that repeated strlen()
on it for each and every line output is wasteful.

Other than that, I didn't spot anything immediately questionable.

Thanks.