Re: [PATCH 2/3] [GSOC] ref-filter: support %(contents) for blob, tree

[ZheNing Hu <adlternative@gmail.com>]

>
> To extend on this point a bit (even though this is not all that
> urgent during the prerelease freeze), conceptually, the %(content)
> field is understood in the larger picture like this:
>
> +--- (the whole thing) ----------------------------------------------+
> |                                                                    |
> | +--- "header" ---------------------------------------------------+ |
> | | tree 678c03dca0a26afd746e8c8bb9e4aadc8bf479b1                  | |
> | | parent 378c7c6ad48c4ccddf9b534616a0e86f28440bd3                | |
> | | author Junio C Hamano <gitster@pobox.com> 1621675665 +0900     | |
> | | committer Junio C Hamano <gitster@pobox.com> 1621675741 +0900  | |
> | +----------------------------------------------------------------+ |
> |                                                                    |
> | +--- "contents" -------------------------------------------------+ |
> | |                                                                | |
> | | +--- "subject" ----------------------------------------------+ | |
> | | | Git 2.32-rc1                                               | | |
> | | +------------------------------------------------------------+ | |
> | |                                                                | |
> | | +--- "body" -------------------------------------------------+ | |
> | | | Signed-off-by: Junio C Hamano <gitster@pobox.com>          | | |
> | | +------------------------------------------------------------+ | |
> | |                                                                | |
> | +----------------------------------------------------------------+ |
> |                                                                    |
> +--------------------------------------------------------------------+
>

Thank you for providing such a complete view. This also means
that the "raw" of contents and tag will contain two parts: "header"
and "contents". But for blobs and trees, they don’t have these things.

> Even though %(header), when it is invented, would make perfect sense
> for commits and tags, it will never make sense for trees and blobs.
> Which means "contents", which is "the whole thing except for the
> header part", would not, either.
>

Although we don’t have a %(header), but in fact we already have fragments
of "%(numparent)", "%(parent)" %(tree)" (see grab_commit_values()) and
"%(tag)"," %(type)","%(object)" (see grab_tag_values()), but they are not
obtained through the "header" part of the raw object buffer.

> There is no %(placeholder) to ask for "the whole thing", and that is
> what you want to use for cat-file --batch if I am not mistaken, and
> adding one would be a good idea.  There is no %(header) yet, either,
> but if somebody needs it for their scripts, it is clear where it fits
> in the picture.
>

So I don't know if adding %(header) will cause duplication of functions.

Thanks!
--
ZheNing Hu