Re: Split commit graphs and commit-graph read

[Jeff King <peff@peff.net>]

On Sun, Nov 10, 2019 at 08:19:20PM -0500, Derrick Stolee wrote:

> > Running some tests with commands like git for-each-ref and git
> > rev-list shows that the "split" commit graph is being used (setting
> > core.commitGraph=false makes commands noticeably slower), so
> > functionally all seems well. But should git commit-graph read be
> > handling this better?
> 
> Unfortunately, you're running into an issue because I designed the
> "read" subcommand poorly (and also forgot to update it for
> incremental commit-graph files). The biggest issue is that "read"
> is not really meant for end-users. It really should have been built
> as a test-tool. This point was corrected when I got around to writing
> the multi-pack-index since it uses "test-tool read-midx" instead of
> add.
> 
> To fix this issue, I would probably go about it by removing the "read"
> subcommand and creating a "test-tool read-commit-graph" for the tests
> that need that output.
> 
> If others on-list think that the better thing to do is to update the
> "read" subcommand to provide the same output, but iterate over each
> layer of an incremental commit-graph, then I can do that work instead.

In theory I suppose one could use it to debug a commit-graph file "in
the field" as it were, where somebody does not necessarily have the
test-tool programs. But in practice, I have not ever done that (I didn't
even know "commit-graph read" was there), and it's not that big a deal
to just have a build of git.git handy.

I'd be much more likely to use "commit-graph verify". And perhaps it
could grow a "--verbose" flag if somebody really wants that (but I think
it would be fine to punt until somebody cares enough to do so).

I guess dropping the sub-command is technically a backwards incompatible
change, but since it didn't do anything that normal users would find
useful in the first place, I wouldn't be sorry to see it go.

-Peff