Re: Assertion failure with git cat-file --batch-command

On Mon, 27 Jul 2026 at 21:26, Pablo Sabater [off-list ref] wrote:

On Mon Jul 27, 2026 at 11:57 AM CEST, Jeff King wrote:

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On Mon, Jul 27, 2026 at 10:30:43AM +0100, Alan Stokes wrote:

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I first observed this in 2.43.0, but it still seems to be present in
2.54.0.

Yeah, I think this has been there since --batch-command was added.

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Note that if I ask git cat-file --batch-command to include the
objecttype in the output it is fine (which gives me a workaround). Or
if I use git cat-file --batch.

IIUC git only fetches the metadata that it needs for each object, and
that is determined from the format. For --batch I guess the type is
always requested, since it is needed to print the object contents. But
for --batch-command that doesn't seem to happen.

Yes, exactly. In the normal --batch code path we have this code:

        /*
         * If we are printing out the object, then always fill in the type,
         * since we will want to decide whether or not to stream.
         */
        if (opt->batch_mode == BATCH_MODE_CONTENTS)
                data.info.typep = &data.type;

But for command mode, we don't do the same. This makes your case work:

diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 1458dd76d6..78eab9723d 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c

@@ -690,6 +690,7 @@ static void parse_cmd_contents(struct batch_options *opt,
                           struct expand_data *data)
 {
      opt->batch_mode = BATCH_MODE_CONTENTS;
+     data->info.typep = &data->type;
      batch_one_object(line, output, opt, data);
 }

but there's a slight catch. That expand_data is used for every request,
not just the current one. In normal --batch mode, every request wants
the same data (the user-specified format plus the object contents). But
in command mode, some may be "contents" requests and some may just be
"info". The code above turns on type-checking for every request, making
the "info" ones pay to look up the type.

Yes, for example, both 'info' and the 'remote-object-info' series
(marked to 'master' in the last "What's cooking") [1] act on
data->info.typep.

This would make 'info' do a type lookup, and 'remote-object-info'
request "type" even if it wasn't present on the format.

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A type lookup isn't all that expensive, but it might matter for some
formats (e.g., just "%(objectname)" does an existence check and nothing
else, so we never even access the object data).

Yes, and only the atoms in the format get expanded, a populated type
without its atom in the format won't be shown.
the wasted lookup or a bigger request are the only effect.

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I guess saving and restore data->info.typep would work.

Yes I think that too, I tried this and it worked fine:

static void parse_cmd_contents(struct batch_options *opt,
                             const char *line,
                             struct strbuf *output,
                             struct expand_data *data)
{
        enum object_type *saved = data->info.typep;

        opt->batch_mode = BATCH_MODE_CONTENTS;
        data->info.typep = &data->type;
        batch_one_object(line, output, opt, data);
        data->info.typep = saved;
}

That does look pretty simple and correct.

nit: On the current code the parameters aren't indented correctly.

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I'm not sure what the correct fix is - always request the type in
--batch-command, or perhaps only if a "contents" command is issued?

Yeah, in general if you are asking about "contents" I'd expect you to
get the full name/type/size triple. But it's not wrong to ask for less,
and certainly we should never hit a BUG(). So I think we'd want a fix
along the lines above.

Do you want to try your hand at a patch? It would need to do the
save/restore, and most importantly add a new test to t1006.

I would be willing to have a go at it. But realistically I probably won't have
time for a month or two. I'm also a complete noob at the whole posting
patches via email process, so it may be slightly chaotic. If anybody else
wanted to deal with it I obviously wouldn't object.

Best wishes,

Alan

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-Peff

[1]: https://lore.kernel.org/git/20260724-ps-eric-work-rebase-v21-0-ba67f024fdff@gmail.com/ (local)

Hope this helps,
Pablo