Subject: [PATCH v3 13/20] commit-graph: verify generation number

From: Derrick Stolee <[email-masked]>
Date: Thu, 24 May 2018 16:25:54 +0000

While iterating through the commit parents, perform the generation
number calculation and compare against the value stored in the
commit-graph.

The tests demonstrate that having a different set of parents affects
the generation number calculation, and this value propagates to
descendants. Hence, we drop the single-line condition on the output.

Signed-off-by: Derrick Stolee <[email-masked]>
---
 commit-graph.c          | 18 ++++++++++++++++++
 t/t5318-commit-graph.sh |  6 ++++++
 2 files changed, 24 insertions(+)

diff --git a/commit-graph.c b/commit-graph.c
index fff22dc0c3..ead92460c1 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -922,6 +922,7 @@ int verify_commit_graph(struct commit_graph *g)
 	for (i = 0; i < g->num_commits; i++) {
 		struct commit *graph_commit, *odb_commit;
 		struct commit_list *graph_parents, *odb_parents;
+		uint32_t max_generation = 0;
 
 		hashcpy(cur_oid.hash, g->chunk_oid_lookup + g->hash_len * i);
 
@@ -956,6 +957,9 @@ int verify_commit_graph(struct commit_graph *g)
 					     oid_to_hex(&graph_parents->item->object.oid),
 					     oid_to_hex(&odb_parents->item->object.oid));
 
+			if (graph_parents->item->generation > max_generation)
+				max_generation = graph_parents->item->generation;
+
 			graph_parents = graph_parents->next;
 			odb_parents = odb_parents->next;
 		}
@@ -963,6 +967,20 @@ int verify_commit_graph(struct commit_graph *g)
 		if (odb_parents != NULL)
 			graph_report("commit-graph parent list for commit %s terminates early",
 				     oid_to_hex(&cur_oid));
+
+		/*
+		 * If one of our parents has generation GENERATION_NUMBER_MAX, then
+		 * our generation is also GENERATION_NUMBER_MAX. Decrement to avoid
+		 * extra logic in the following condition.
+		 */
+		if (max_generation == GENERATION_NUMBER_MAX)
+			max_generation--;
+
+		if (graph_commit->generation != max_generation + 1)
+			graph_report("commit-graph generation for commit %s is %u != %u",
+				     oid_to_hex(&cur_oid),
+				     graph_commit->generation,
+				     max_generation + 1);
 	}
 
 	return verify_commit_graph_error;
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 12f0d7f54d..673b0d37d5 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -272,6 +272,7 @@ GRAPH_BYTE_COMMIT_TREE=$GRAPH_COMMIT_DATA_OFFSET
 GRAPH_BYTE_COMMIT_PARENT=`expr $GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN`
 GRAPH_BYTE_COMMIT_EXTRA_PARENT=`expr $GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 4`
 GRAPH_BYTE_COMMIT_WRONG_PARENT=`expr $GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 3`
+GRAPH_BYTE_COMMIT_GENERATION=`expr $GRAPH_COMMIT_DATA_OFFSET + $HASH_LEN + 8`
 
 # usage: corrupt_graph_and_verify <position> <data> <string>
 # Manipulates the commit-graph file at the position
@@ -366,4 +367,9 @@ test_expect_success 'detect incorrect tree OID' '
 		"commit-graph parent for"
 '
 
+test_expect_success 'detect incorrect generation number' '
+	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION "\01" \
+		"generation"
+'
+
 test_done
-- 
2.16.2.329.gfb62395de6