Re: [RFC/WIP] range-diff: show old/new blob OIDs in comments

> (WIP, mostly stream-of-concious notes + reasoning)
>
> When using "git format-patch --range-diff", the pre and
> post-image blob OIDs are in each email, while the exact
> commit OIDs are rarely shared via emails (only the tip
> commit from "git request-pull").
>
> These blob OIDs make it easy to search for or lookup the
> full emails which create them, or the blob itself once
> it's fetched via git.
>
> public-inbox indexes and allows querying specifically for blob
> OIDs via dfpre:/dfpost: since June 2017.  As of Jan 2019,
> public-inbox also supports recreating blobs out of patch emails
> (querying internally with dfpre:/dfpost: and doing "git apply")
>
> Searching on these blob OIDs also makes it easier to find
> previous versions of the patch sets using any mail search
> engine.
>
> Future changes to public-inbox may allow generating custom
> diffs out of any blobs it can find or recreate.
>
> Most of this is pretty public-inbox-specific and would've
> made some future changes to public-inbox much easier....
> (if we had this from the start of range-diff).
>
> Unfortunately, it won't help with cases where range-diffs
> are already published, but range-diff isn't too old.

>
> I'm also still learning my way around git's C internals, but
> using patch.{old,new}_oid_prefix seems alright...
>
> FIXME: tests, t3206 needs updating
>
> Not-signed-off-by: Eric Wong <e@80x24.org>
> ---
>  range-diff.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/range-diff.c b/range-diff.c
> index 7fed5a3b4b..85d2f1f58f 100644
> --- a/range-diff.c
> +++ b/range-diff.c
> @@ -118,13 +118,24 @@ static int read_patches(const char *range, struct string_list *list)
>  				die(_("could not parse git header '%.*s'"), (int)len, line);
>  			strbuf_addstr(&buf, " ## ");
>  			if (patch.is_new > 0)
> -				strbuf_addf(&buf, "%s (new)", patch.new_name);
> +				strbuf_addf(&buf, "%s (new %s)",
> +						patch.new_name,
> +						patch.new_oid_prefix);
>  			else if (patch.is_delete > 0)
> -				strbuf_addf(&buf, "%s (deleted)", patch.old_name);
> +				strbuf_addf(&buf, "%s (deleted %s)",
> +						patch.old_name,
> +						patch.old_oid_prefix);
>  			else if (patch.is_rename)
> -				strbuf_addf(&buf, "%s => %s", patch.old_name, patch.new_name);
> +				strbuf_addf(&buf, "%s => %s (%s..%s)",
> +						patch.old_name,
> +						patch.new_name,
> +						patch.old_oid_prefix,
> +						patch.new_oid_prefix);
>  			else
> -				strbuf_addstr(&buf, patch.new_name);
> +				strbuf_addf(&buf, "%s (%s..%s)",
> +						patch.new_name,
> +						patch.old_oid_prefix,
> +						patch.new_oid_prefix);
>
>  			free(current_filename);
>  			if (patch.is_delete > 0)
>
>