Re: GSoC Git Proposal Draft - ZheNing Hu

[ZheNing Hu <adlternative@gmail.com>]

Jeff King <peff@peff.net> 于2021年4月8日周四 上午3:28写道：
>
> On Sat, Apr 03, 2021 at 10:27:39PM +0800, ZheNing Hu wrote:
>
> > >   - figure out which data will be needed for each item based on the
> > >     parsed format, and then do the minimum amount of work to get that
> > >     data (using "oid_object_info_extended()" helps here, because it
> > >     likewise tries to do as little work as possible to satisfy the
> > >     request, but there are many elements that it doesn't know about)
> > >
> >
> > I have indeed noticed that `oid_object_info_extended()`
> > can get information about the object which we actually want.
> > In `cat-file.c`, It has been used in `batch_object_write()`, and
> > `expanding_atom()` specify what data we need.
> > In `ref-filter.c`, It has been used in `get_object()`.
> > I am not sure what you mean about "many elements that it
> > doesn't know about", For the time being, `cat-file` can get 5
> > kind of objects info it need.
>
> I think there are things one might want to format that
> oid_object_info_extended() does not know about. For example, if you are
> asking about %(authorname), it can't provide that. But we want to do as
> little work as possible to satisfy the request. So for example, with the
> format "%(objectsize)", we'd prefer _not_ to load the contents of each
> object, and just ask oid_object_info_extended() for the size. But if we
> are asked for "%(authorname)", we know we'll have to read and parse the
> object contents.
>

OK, I understand it now, `%(authorname)` needs to grub info in object content
so that content must be parsed, If we need to let cat-file learn
`%(authorname)`,
It takes extra work to extract from the object.

> So this notion of "figure out the least amount of work" will have to be
> part of the format code (and ref-filter and the pretty.c formatters do
> make an attempt at this; I'm saying that a universal formatter will want
> to keep this behavior).
>

You're right. %(tree) %(parent) ... reliant on commit object info,
%(tagger) %(taggername) ... reliant on tag object info.But If it is
some %(objectsize) or %(objectname) content, we do not need
to parse the content of the objects. Future work we should also
keep avoid parsing of non-dependent info.

> > Maybe you think that `cat-file` can learn some features in
> > `ref-filter` to extend the function of `cat-file --batch`?
> > E.g. %(objectname:short)? I think I may have a better
> > understanding of the topic of this mini-project now.
> > We may not want to port the logic of cat-file,but to learn some
> > design in `ref-filter`, right?
>
> Yes, I think the goal is for all of the commands that allow format
> specifiers to support the same set (at least where it makes sense;
> obviously you cannot ask for %(refname) in cat-file).
>

The future new API may need to deny such access.

> And IMHO the best way to do that is to write a new universal formatting
> API that takes the best parts from all of the existing ones. It _could_
> also be done by choosing ref-filter as the best implementation, slowly
> teaching it formats the other commands know (which is what Olga had
> started with), and then cleaning up any performance deficiencies. But I
> think that last part would actually be easier when starting from scratch
> (e.g., I think it would help to actually produce an abstract syntax tree
> of the parsed format, and then walk that tree to fill in the values).
>
> -Peff

It is the unified "%an" and "%author" you said last time.
I think maybe Olga and Hariom might have done similar things:
Calling `ref-filter` results in slower speed.

And you said we may can refactor to abstract syntax tree, this is
a good idea, and this may be a big project, In particular, pre-knowledge
of compilation principles is required, and we may also need to deal with
each different atom carefully.

Thanks.
--
ZheNing Hu