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commit-graph: return generation from memory

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The commit_graph_generation() method used to report a value of
GENERATION_NUMBER_INFINITY if the commit_graph_data_slab had an instance
for the given commit but the graph_pos indicated the commit was not in
the commit-graph file.

However, an upcoming change will introduce the ability to set generation
values in-memory without writing the commit-graph file. Thus, we can no
longer trust 'graph_pos' to indicate whether or not the generation
member can be trusted.

Instead, trust the 'generation' member if the commit has a value in the
slab _and_ the 'generation' member is non-zero. Otherwise, treat it as
GENERATION_NUMBER_INFINITY.

This only makes a difference for a very old case for the commit-graph:
the very first Git release to write commit-graph files wrote zeroes in
the topological level positions. If we are parsing a commit-graph with
all zeroes, those commits will now appear to have
GENERATION_NUMBER_INFINITY (as if they were not parsed from the
commit-graph).

I attempted several variations to work around the need for providing an
uninitialized 'generation' member, but this was the best one I found. It
does require a change to a verification test in t5318 because it reports
a different error than the one about non-zero generation numbers.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee 2023-03-20 11:26:51 +00:00 committed by Junio C Hamano
parent 80c928d947
commit 2ee11f7261
2 changed files with 4 additions and 6 deletions
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8
commit-graph.c
View file

@ -116,12 +116,10 @@ timestamp_t commit_graph_generation(const struct commit *c)
struct commit_graph_data *data =
commit_graph_data_slab_peek(&commit_graph_data_slab, c);
if (!data)
return GENERATION_NUMBER_INFINITY;
else if (data->graph_pos == COMMIT_NOT_FROM_GRAPH)
return GENERATION_NUMBER_INFINITY;
if (data && data->generation)
return data->generation;
return data->generation;
return GENERATION_NUMBER_INFINITY;
}
static struct commit_graph_data *commit_graph_data_at(const struct commit *c)

2
t/t5318-commit-graph.sh
View file

@ -630,7 +630,7 @@ test_expect_success 'detect incorrect generation number' '
test_expect_success 'detect incorrect generation number' '
corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION "\01" \
"non-zero generation number"
"commit-graph generation for commit"
'
test_expect_success 'detect incorrect commit date' '