Re: [PATCH] [GSOC] ref-filter: add %(notes) format atom

From: ZheNing Hu <adlternative@gmail.com>
Date: May 3, 2021, 13:25 UTC
Message-ID: <CAOLTT8R2-uZQ4rAs+TNKSZXzfXjjB-=unuBUykMo=taguTPw7A@mail.gmail.com>
In-Reply-To: <xmqqsg34a5j8.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> 于2021年5月3日周一 上午10:57写道：

Show 13 quoted lines

>
> ZheNing Hu <adlternative@gmail.com> writes:
>
> > Note that `cat-file --batch` should be a superset of `ref-filter` and
> > `--pretty`, because
> > it supports all objects, while `ref-filter` only supports "commit" and
> > "tag" two kinds
> > of objects, and `--pretty` only supports "commit" one kind of object.
>
> What?  A ref can point at any kind of objects, not necessarily
> commits and tags.  %(objectname), %(objecttype), etc. obviously
> are applicable to any type of object.
>

Thanks for correcting. I only saw tag and commit in the output of `git for-each-ref` before, and blob and tree are not processed in `grab_values` in `ref-filter.c`, which deepens my illusion. `git update-ref` can make a ref point to a blob object or tree object, although I don't know what these refs are used for... A reference to a commit object makes sense, but if it is a blob, are there any suitable scenarios?

> Another thing worth noting is that ref-filter needs to deal with
> traits that are not tied to any particular object, but to the ref
> itself, like who its upstream is and where it would be pushed to.
>

Indeed need to be considered "%(push)" "%(remote)" will change "refname".

Show 11 quoted lines

> > So it may be reasonable to provide `%(notes)` to "commit","tag"
> > objects in `cat-file --batch`
> > in the future, now integrate them into ref-filter firstly.
>
> And you can attach notes to objects of any type, not limited to
> commits and tags.
>
> >> >     So in this patch, I tried to migrate --pretty=%N to --format=%(notes).
>
> What do you mean by "migrate"?  Are you making both available?
>

Well, here are some incorrect statements, I just want to express that the `--format="%(notes)"` implemented in "ref-filter" has the same semantics as "--pretty=%N".

Show 16 quoted lines

> >> > diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
> >> > index 2ae2478de706..07f037a16e13 100644
> >> > --- a/Documentation/git-for-each-ref.txt
> >> > +++ b/Documentation/git-for-each-ref.txt
> >> > @@ -139,6 +139,9 @@ deltabase::
> >> >       given object, if it is stored as a delta.  Otherwise it
> >> >       expands to the null object name (all zeroes).
> >> >
> >> > +notes::
> >> > +     The notes associated with the ref.
>
> "The notes associated with the object pointed at by the ref".
>
> A note is never associated with a ref.  It can only associated with
> an object.
>

Indeed.

Show 17 quoted lines

> If we are going to have %(notes), it may be natural to desire
> grabbing notes for the given object from specified notes ref, e.g.
>
>     git for-each-ref --format="%(notes:amlog) %(subject)" zh/pretty-date-human
>
> may want to give the same kind of information as
>
>     git show -s --format='%N %s' --notes=amlog zh/pretty-date-human
>
> The underlying notes machinery however may not be prepared to work
> with more than one notes tree at the same time, so
>
>     git for-each-ref --format="%(notes) %(subject)" --notes=amlog zh/pretty-date-human
>
> might be a better syntax, as --format="%(notes:X) %(notes:Y)" may
> not be something you can easily support.
>

Here is a "bad" idea that might support this feature: use another subprocess "git notes --refs=refs/notes/amlog" :)

Thanks. -- ZheNing Hu