Re: [PATCH v2 0/4] cat-file: optionally convert to worktree version

[Jeff King <peff@peff.net>]

On Wed, Aug 24, 2016 at 10:02:39AM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > On Wed, Aug 24, 2016 at 09:09:06AM -0700, Junio C Hamano wrote:
> >
> >> >  +	if (!path)
> >> >  +		path = obj_context.path;
> >> >  +	else if (obj_context.mode == S_IFINVALID)
> >> >  +		obj_context.mode = 0100644;
> >> >  +
> >> >   	buf = NULL;
> >> >   	switch (opt) {
> >> >   	case 't':
> >> 
> >> The above two hunks make all the difference in the ease of reading
> >> the remainder of the function.  Very good.
> >
> > Yeah, I agree. Though it took me a moment to figure out why we were
> > setting obj_context.mode but not obj_context.path; the reason is that
> > "mode" is convenient to use as local storage, but "path" is not, because
> > it is not a pointer but an array.
> 
> Wait a minute.  Why is it a cascaded if/elseif, not two independent
> if statements that gives a default value?  In other words, wouldn't
> these two independent and orthogonal decisions?
> 
>  * When forced to use some path, we ignore obj_context.path
> 
>  * Whether we are forced to use a path or not, if we do not know the
>    mode from the lookup context, we want to use the regular blob
>    mode.
> 
> So that part of the patch is wrong after all, I would have to say.
> 
> 	if (!path)
>         	path = obj_context.path;
> 	if (obj_context.mode == S_IFINVALID)
>         	obj_context.mode = 0100644;
> 
> or something like that, perhaps.

Oh, hrm, you are right. I assumed we wanted to force the mode when
--path was in effect, but that is not what the original does. If you
say:

  --path=foo HEAD:bar

then we will take the mode for "bar", whatever it is (maybe a tree or
symlink). But if you say:

  --path=foo $(git rev-parse HEAD:bar)

then we will use 100644, regardless of what "bar" is in HEAD.

I have not thought about it enough to know if that is a good thing or a
bad thing. But I'll bet Dscho has, so I will wait for him to comment. :)

> >   if (!force_path) {
> > 	/* use file info from sha1 lookup */
> > 	path = obj_context.path;
> > 	mode = obj_context.mode;
> >   } else {
> > 	/* use path requested by user, and assume it is a regular file */
> > 	path = force_path;
> > 	mode = 0100644;
> >   }
> 
> Hmph, if you read it that way, then if/elseif makes some sense, but
> we need to assume that the obj_context.mode can be garbage and have
> a fallback for it.
> 
> Just like
> 
> 	git cat-file --filters --path=git.c HEAD:t
> 
> would error out because HEAD:t is not even a blob, I would expect
> 
> 	git cat-file --filters --path=git.c :RelNotes
> 
> to error out, because the object itself _is_ known to be a
> blob that is not a regular file.
> 
> And that kind of type checking will not be possible with "if the
> user gave us a path, assume it is a regular file".

Right, I agree that is the outcome, but I just wasn't sure that the
second case _should_ error out. IOW, does "--filters --path" mean "treat
this as a regular file at path X", or is the "regular file" part not
implied?

I don't suppose anybody cares that much either way, but it feels weird
to behave differently depending on how we looked up the blob (whereas
for the HEAD:t case, a tree is always a tree).

-Peff