Subject: [RFC PATCH 0/1] commit-graph.c: handle corrupt commit trees

From: Taylor Blau <[email-masked]>
Date: Tue, 3 Sep 2019 22:22:38 -0400

Hi,

I was running some of the new 'git commit-graph' commands, and noticed
that I could consistently get 'git commit-graph write --reachable' to
segfault when a commit's root tree is corrupt.

I have an extremely-unfinished fix attached as an RFC PATCH below, but I
wanted to get a few thoughts on this before sending it out as a non-RFC.

In my patch, I simply 'die()' when a commit isn't able to be parsed
(i.e., when 'parse_commit_no_graph' returns a non-zero code), but I
wanted to see if others thought that this was an OK approach. Some
thoughts:

  * It seems like we could write a commit-graph by placing a "filler"
    entry where the broken commit would have gone. I don't see any place
    where this is implemented currently, but this seems like a viable
    alternative to not writing _any_ commits into the commit-graph.

  * Could we learn about the corruption earlier? Ideally (in the obscene
    of these placeholder objects that indicate corruption), we wouldn't
    start writing a commit-graph until all of the objects in it are
    known to be good.

    This seems like a costly operation when it comes to memory, but
    maybe I'm thinking about it the wrong way.

Depending on the approach here, I'll clean up the commit and message, as
well as add a test that demonstrates the breakage and subsequent fix.

Thanks in advance for your feedback :-).

Taylor Blau (1):
  commit-graph.c: die on un-parseable commits

 commit-graph.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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2.22.0