[PATCH v3 4/4] commit-graph: commit-graph: avoid repeated mixed generation number warnings

[Taylor Blau <me@ttaylorr.com>]

When validating that a commit-graph has either all zero, or all non-zero
generation numbers, we emit a warning on both the rising and falling
edge of transitioning between the two.

So if we are unfortunate enough to see a commit-graph which has a
repeating sequence of zero, then non-zero generation numbers, we'll
generate many warnings that contain more or less the same information.

Avoid this by keeping track of a single example for a commit with zero-
and non-zero generation, and emit a single warning at the end of
verification if both are non-NULL.

Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 commit-graph.c          | 29 +++++++++++++----------------
 t/t5318-commit-graph.sh |  4 ++--
 2 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/commit-graph.c b/commit-graph.c
index acca753ce8..9e6eaa8a46 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -2560,9 +2560,6 @@ static void graph_report(const char *fmt, ...)
 	va_end(ap);
 }
 
-#define GENERATION_ZERO_EXISTS 1
-#define GENERATION_NUMBER_EXISTS 2
-
 static int commit_graph_checksum_valid(struct commit_graph *g)
 {
 	return hashfile_checksum_valid(g->data, g->data_len);
@@ -2575,7 +2572,8 @@ static int verify_one_commit_graph(struct repository *r,
 {
 	uint32_t i, cur_fanout_pos = 0;
 	struct object_id prev_oid, cur_oid;
-	int generation_zero = 0;
+	struct commit *seen_gen_zero = NULL;
+	struct commit *seen_gen_non_zero = NULL;
 
 	verify_commit_graph_error = verify_commit_graph_lite(g);
 	if (verify_commit_graph_error)
@@ -2681,19 +2679,12 @@ static int verify_one_commit_graph(struct repository *r,
 			graph_report(_("commit-graph parent list for commit %s terminates early"),
 				     oid_to_hex(&cur_oid));
 
-		if (!commit_graph_generation_from_graph(graph_commit)) {
-			if (generation_zero == GENERATION_NUMBER_EXISTS)
-				graph_report(_("commit-graph has generation number zero for commit %s, but non-zero elsewhere"),
-					     oid_to_hex(&cur_oid));
-			generation_zero = GENERATION_ZERO_EXISTS;
-		} else {
-			if (generation_zero == GENERATION_ZERO_EXISTS)
-				graph_report(_("commit-graph has non-zero generation number for commit %s, but zero elsewhere"),
-					     oid_to_hex(&cur_oid));
-			generation_zero = GENERATION_NUMBER_EXISTS;
-		}
+		if (commit_graph_generation_from_graph(graph_commit))
+			seen_gen_non_zero = graph_commit;
+		else
+			seen_gen_zero = graph_commit;
 
-		if (generation_zero == GENERATION_ZERO_EXISTS)
+		if (seen_gen_zero)
 			continue;
 
 		/*
@@ -2719,6 +2710,12 @@ static int verify_one_commit_graph(struct repository *r,
 				     odb_commit->date);
 	}
 
+	if (seen_gen_zero && seen_gen_non_zero)
+		graph_report(_("commit-graph has both zero and non-zero "
+			       "generations (e.g., commits '%s' and '%s')"),
+			     oid_to_hex(&seen_gen_zero->object.oid),
+			     oid_to_hex(&seen_gen_non_zero->object.oid));
+
 	return verify_commit_graph_error;
 }
 
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 8e96471b34..ba65f17dd9 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -620,12 +620,12 @@ test_expect_success 'detect incorrect chunk count' '
 
 test_expect_success 'detect mixed generation numbers (non-zero to zero)' '
 	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION_LAST "\0\0\0\0" \
-		"but non-zero elsewhere"
+		"both zero and non-zero generations"
 '
 
 test_expect_success 'detect mixed generation numbers (zero to non-zero)' '
 	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION "\0\0\0\0" \
-		"but zero elsewhere"
+		"both zero and non-zero generations"
 '
 
 test_expect_success 'git fsck (checks commit-graph when config set to true)' '
-- 
2.42.0.4.g52b49bb434