Re: [PATCH 0/3] cat-file: add %(objectmode) avoid verifying submodules' OIDs

[Jeff King <peff@peff.net>]

On Mon, Mar 11, 2024 at 02:43:00PM -0700, Junio C Hamano wrote:

> It is somewhat unsatisfying that --batch/--batch-check lacks so
> much.  Even with %(objectmode) its nature of one-object-at-a-time
> makes querying children of a large tree a chore, when you compare it
> with something like "cat-file -p HEAD:" that allows you to grab the
> needed information for all children with a single invocation.
> 
> This is orthogonal to what the patch wants to do, which is to enrich
> the output side with more formatting, bit I wonder if we want to
> consider enriching the input side?  e.g. instead of feeding just a
> single object name from the standard input of "cat-file
> --batch/--batch-check", perhaps a syntax can say "Here I have the
> object name for a tree-ish object, but please pretend that I gave
> you all the objects contained within it", or something?

That is an interesting direction. In practice I guess you might want to
expand trees (to show their contents) or perhaps commits (to traverse
history and/or look at their trees). And we already have tools to do
that.

So for example you can already do:

  git ls-tree --format='%(objectname) %(objectmode)' HEAD

Or if you wanted to mix-and-match with other cat-file placeholders, you
can do:

  git ls-tree --format='%(objectname) %(objectmode)' HEAD |
  git cat-file --batch-check='%(objectname) %(deltabase) %(rest)'

That is a little less efficient (we look up the object twice), but once
you are working with hex object ids it is not too bad (cat-file is
heavily optimized here). Of course in the long run I think we should
move to a future where the formatting code is shared, and you can just
ask ls-tree for deltabase if you want to.

I think leaving this to specialized tools like ls-tree gives them a lot
of flexibility that a special input mode to cat-file might find awkward.
For example, recurse vs non-recursive tree listing. Or filtering with
pathspecs. And of course when you get into commits and traversal, there
are many rev-list options. :)

The strategy so far has been making sure cat-file can efficiently take
in the output of these other tools to further describe objects. But
moving towards a unified output formatting model would be even better, I
think. In the meantime, I think cat-file learning %(objectmode) makes
sense for single names (rather than listing trees), and fortunately it
uses the same (obvious) name that ls-tree does, so we won't have a
problem unifying them later.

The patch itself looked reasonable to me, modulo the comments you
already made.

-Peff