When upgrading a commit-graph using generation v1 to one using
generation v2, it is possible to force Git into a corrupt state where it
(incorrectly) believes that a GDO2 chunk is necessary, *after* deciding
not to write one.
This makes subsequent reads using the commit-graph produce the following
error message:
fatal: commit-graph requires overflow generation data but has none
Demonstrate this bug by increasing our test coverage to include a
minimal example of upgrading a commit-graph from generation v1 to v2.
The only notable components of this test are:
- The committer date of the commit is chosen carefully so that the
offset underflows when computed using a v1 generation number, but
would not overflow when using v2 generation numbers.
- The upgrade to generation number v2 must read in the v1 generation
numbers, which we can do by passing `--changed-paths`, which will
force the commit-graph internals to call `fill_commit_graph_info()`.
A future patch will squash this bug.
Reported-by: Jeff King <peff@xxxxxxxx>
Reproduced-by: Will Chandler <wfc@xxxxxxxxxxxxxx>
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
t/t5318-commit-graph.sh | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index fbf0d64578..4d9f62f22d 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -811,4 +811,31 @@ test_expect_success 'set up and verify repo with generation data overflow chunk'
graph_git_behavior 'generation data overflow chunk repo' repo left right
+test_expect_failure 'overflow during generation version upgrade' '
+ git init overflow-v2-upgrade &&
+ (
+ cd overflow-v2-upgrade &&
+
+ # This commit will have a date at two seconds past the Epoch,
+ # and a (v1) generation number of 1, since it is a root commit.
+ #
+ # The offset will then be computed as 2-1, which will underflow
+ # to 2^31, which is greater than the v2 offset small limit of
+ # 2^31-1.
+ #
+ # This is sufficient to need a large offset table for the v2
+ # generation numbers.
+ test_commit --date "@2 +0000" base &&
+ git repack -d &&
+
+ # Test that upgrading from generation v1 to v2 correctly
+ # produces the overflow table.
+ git -c commitGraph.generationVersion=1 commit-graph write &&
+ git -c commitGraph.generationVersion=2 commit-graph write \
+ --changed-paths &&
+
+ git rev-list --all
+ )
+'
+
test_done
--
2.37.0.1.g1379af2e9d
