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[PATCH 0/1] commit-graph: writing missing parents is a BUG

A user complained that they had the following message in a git command:

fatal: invalid parent position 2147483647

In hex, this value is 0x7fffffff, corresponding to the GRAPH_MISSING_PARENT
constant. This constant was intended as a way to have the commit-graph store
commits with parents that are not also in the commit-graph. During
development, however, we chose to require the commit-graph to be closed
under reachability. Thus, this value should never be written, and we don't
fall back to parsing usual commits when we see the constant.

This actually happened, and the root cause is unknown. This either means the
reachable closure logic is broken somewhere, or something caused the binary
search to find the parent in our list of commits. This second problem is
more likely, as we have seen RAM issues cause corrupted memory before. I'm
still investigating the root cause, but for now we can hit a BUG() statement
instead of writing bad data.

Thanks, -Stolee

Derrick Stolee (1):
  commit-graph: writing missing parents is a BUG

 commit-graph.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

base-commit: 0d0ac3826a3bbb9247e39e12623bbcfdd722f24c
Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-102%2Fderrickstolee%2Fcommit-graph-bug-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-102/derrickstolee/commit-graph-bug-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/102