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commit-graph: fix ordering bug in generation numbers 

When computing the generation numbers for a commit-graph, we compute
the corrected commit dates and then check if their offsets from the
actual dates is too large to fit in the 32-bit Generation Data chunk.
However, there is a problem with this approach: if we have parsed the
generation data from the previous commit-graph, then we continue the
loop because the corrected commit date is already computed. This causes
an under-count in the number of overflow values.

It is incorrect to add an increment to num_generation_data_overflows
next to this 'continue' statement, because we might start
double-counting commits that are computed because of the depth-first
search walk from a commit with an earlier OID.

Instead, iterate over the full commit list at the end, checking the
offsets to see how many grow beyond the maximum value.

Create a new t5328-commit-graph-64-bit-time.sh test script to handle
special cases of testing 64-bit timestamps. This helps demonstrate this
bug in more cases. It still won't hit all potential cases until the next
change, which reenables reading generation numbers. Use the skip_all
trick from 0a2bfccb9c (t0051: use "skip_all" under !MINGW in
single-test file, 2022-02-04) to make the output clean when run on a
32-bit system.

Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee 2022-03-01 19:48:30 +00:00 committed by Junio C Hamano
parent 17925e0602
commit 75979d9460
3 changed files with 48 additions and 5 deletions
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10
commit-graph.c
View File

@ -1556,12 +1556,16 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
if (current->date && current->date > max_corrected_commit_date)
max_corrected_commit_date = current->date - 1;
commit_graph_data_at(current)->generation = max_corrected_commit_date + 1;
if (commit_graph_data_at(current)->generation - current->date > GENERATION_NUMBER_V2_OFFSET_MAX)
ctx->num_generation_data_overflows++;
}
}
}
for (i = 0; i < ctx->commits.nr; i++) {
struct commit *c = ctx->commits.list[i];
timestamp_t offset = commit_graph_data_at(c)->generation - c->date;
if (offset > GENERATION_NUMBER_V2_OFFSET_MAX)
ctx->num_generation_data_overflows++;
}
stop_progress(&ctx->progress);
}

4
t/t5318-commit-graph.sh
View File

@ -425,10 +425,10 @@ test_expect_success 'warn on improper hash version' '
)
'
test_expect_success 'lower layers have overflow chunk' '
test_expect_success TIME_IS_64BIT,TIME_T_IS_64BIT 'lower layers have overflow chunk' '
cd "$TRASH_DIRECTORY/full" &&
UNIX_EPOCH_ZERO="@0 +0000" &&
FUTURE_DATE="@2147483646 +0000" &&
FUTURE_DATE="@4147483646 +0000" &&
rm -f .git/objects/info/commit-graph &&
test_commit --date "$FUTURE_DATE" future-1 &&
test_commit --date "$UNIX_EPOCH_ZERO" old-1 &&

39
t/t5328-commit-graph-64bit-time.sh Executable file
View File

@ -0,0 +1,39 @@
#!/bin/sh
test_description='commit graph with 64-bit timestamps'
. ./test-lib.sh
if ! test_have_prereq TIME_IS_64BIT || ! test_have_prereq TIME_T_IS_64BIT
then
skip_all='skipping 64-bit timestamp tests'
test_done
fi
. "$TEST_DIRECTORY"/lib-commit-graph.sh
UNIX_EPOCH_ZERO="@0 +0000"
FUTURE_DATE="@4147483646 +0000"
GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
test_expect_success 'lower layers have overflow chunk' '
rm -f .git/objects/info/commit-graph &&
test_commit --date "$FUTURE_DATE" future-1 &&
test_commit --date "$UNIX_EPOCH_ZERO" old-1 &&
git commit-graph write --reachable &&
test_commit --date "$FUTURE_DATE" future-2 &&
test_commit --date "$UNIX_EPOCH_ZERO" old-2 &&
git commit-graph write --reachable --split=no-merge &&
test_commit extra &&
git commit-graph write --reachable --split=no-merge &&
git commit-graph write --reachable &&
graph_read_expect 5 "generation_data generation_data_overflow" &&
mv .git/objects/info/commit-graph commit-graph-upgraded &&
git commit-graph write --reachable &&
graph_read_expect 5 "generation_data generation_data_overflow" &&
test_cmp .git/objects/info/commit-graph commit-graph-upgraded
'
graph_git_behavior 'overflow' '' HEAD~2 HEAD
test_done