Re: [PATCH] commit-graph: add verify changed paths option

[Taylor Blau <me@ttaylorr.com>]

On Fri, Jul 31, 2020 at 02:02:35PM -0400, Jeff King wrote:
> On Fri, Jul 31, 2020 at 07:49:25AM +0000, Son Luong Ngoc via GitGitGadget wrote:
>
> > From: Son Luong Ngoc <sluongng@gmail.com>
> >
> > Add '--has-changed-paths' option to 'git commit-graph verify' subcommand
> > to validate whether the commit-graph was written with '--changed-paths'
> > option.
>
> Is a single boolean flag sufficient? If you have incrementals, you might
> have some slices with this chunk and some without. What should the
> boolean be in that case?

I think you'd really want to know which layers do and don't have
filters. It might be even more interesting to have a tool like what 'git
show-index' is to '*.idx' files, maybe something like 'git show-graph'
or 'git show-commit-graph'. Its output would be one line per commit that
shows:

  - what layer in the chain it's located at
  - its graph_pos
  - its generation number
  - whether or not it has a Bloom filter
  - ???

That would be a useful tool for debugging anyway, even outside of the
test suite. It would be even better if we could replace the test-tool
with it.

On an unrelated note; this patch is broken as-is, since it will only
report that Bloom filters exist if the top-most graph has them. I have a
patch to fix this that I have been meaning to send out for most of this
week. I'll try to get to it shortly.

> I thought we had some way of reporting the number of commits covered by
> filters, but I can't seem to find it.

I don't recall having anything like that.

> Our "test-tool read-graph" can report on whether there's a bloom filter
> chunk, but I think it also doesn't distinguish between different slices
> (and anyway, it wouldn't be suitable for tools that don't rely on an
> actual built git.git directory).
>
> -Peff
Thanks,
Taylor