Re: [PATCH 4/6] [GSOC] ref-filter: add %(rest) atom and --rest option

Junio C Hamano [off-list ref] 于2021年6月9日周三 下午3:00写道：

I think I kind-of see what is going on here.  There is

    git cat-file blob --textconv --path="$path" "$blob_object_name"

that allows a blob to be fed to the command, pretend as if it
appears at $path in a tree object and grab attribute for it, and
show the blob contents converted using the textconv filter.  If we
were to mimic it by extending the format based substitutions, a
design consistent with the behaviour is to teach --format=%(raw)
to show the contents after applying the textconv filter instead of
the raw blob contents.

Yes, this is exactly what cat-file --textconv does.

And there is a corresponding

    git cat-file --batch --textconv

The "--path=$path" parameter is omitted when using --batch, as each
object would sit at different path in the tree (so the input stream
would be given as a run of "<blob> <path>" to give each item its own
path).

Just like let --batch omitted --path, --rest is meaningless for "for-ech-ref".

So to answer my question in the previous message, yes, this is an
attempt to support the "cat-file --textconv".  So in the context of
that command, something may need to be added.  But I do not think it
makes any sense to expose that to for-each-ref and friends, even if
we were to share the internal machinery (after all, sharing of the
internal machinery is a mere means to an end that is to make it
easier to give the same syntax and same behaviour to end users and
is not a goal itself; "because we use the same machinery, the users
have to tolerate that irrelevant %(atoms) are accepted by the parser"
is not making a good excuse for a sloppy implementation).

Because "git cat-file --batch" will only print the contents of the object once,
so when implements the function of textconv/filters in ref-filter,
we should really consider whether we should let something like
"%(raw) %(raw) %(raw) %(raw:size)" all pass the conversion of textconv/filters.
If it is my previous %(raw:textconv) or %(raw:filter), they can only print
the converted content separately, and we need:

$ git for-ecah-ref --format="%(raw:filters) %(raw:filters)
%(raw:filters) %(raw:filters:size)"

As you said it might be too complicated for the user....

Having said all that, I somehow doubt that the "--batch=<format>"
was designed to interact sensibly with the "--textconv" option.
builtin/cat-file.c::expand_atom() does not know anything at all that
the data could be modified from the raw contents of the blob, so
--batch="%(contents) %(size)" --textconv, if existed, may show the
conveted contents with size of blob before conversion, or something
incoherent like that.  And if your rewrite using the shared internal
machinery results in a more coherent behaviour, that would be
excellent.  For example, we could imagine that the machinery, when
textconv (or filter) is in use, would first grab the blob contents
and run the requested conversion, and then work solely on that
conveted contents when computing what to fill with %(raw:size) and
other blob-related atoms.

And with your --textconv/--filters, we only need:

$ git for-ecah-ref --format="%(raw) %(raw) %(raw) %(raw:size)" --filters

This will be more concise for users. I will try to build --filters, --textconv
for ref-filter . But as stated in the previous reply, it needs to be placed
after the transplant of cat-file --batch (Because --path is useless for
for-each-ref, and at the same time we need proper testing for
--filter/--textconv.)

Thanks, your reply is very reasonable,
--
ZheNing Hu