[PATCH v2 06/12] bloom: use num_changes not nr for limit detection

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: May 11, 2020, 11:56 UTC
Message-ID: <8278b5c0918c6b357e1f1ab3ee65ed2091ec3f61.1589198180.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.622.v2.git.1589198180.gitgitgadget@gmail.com>

From: Derrick Stolee <dstolee@microsoft.com>

As diff_tree_oid() computes a diff, it will terminate early if the total number of changed paths is strictly larger than max_changes. This includes the directories that changed, not just the file paths. However, only the file paths are reflected in the resulting diff queue's "nr" value.

Use the "num_changes" from diffopt to check if the diff terminated early. This is incredibly important, as it can result in incorrect filters! For example, the first commit in the Linux kernel repo reports only 471 changes, but since these are nested inside several directories they expand to 513 "real" changes, and in fact the total list of changes is not reported. Thus, the computed filter for this commit is incorrect.

Demonstrate the subtle difference by using one fewer file change in the 'get bloom filter for commit with 513 changes' test. Before, this edited 513 files inside "bigDir" which hit this inequality. However, dropping the file count by one demonstrates how the previous inequality was incorrect but the new one is correct.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 bloom.c          | 2 +-
 t/t0095-bloom.sh | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/bloom.c b/bloom.c
index 196cda0a1bd..e2ede44126c 100644
--- a/bloom.c
+++ b/bloom.c
@@ -215,7 +215,7 @@ struct bloom_filter *get_bloom_filter(struct repository *r,
 		diff_tree_oid(NULL, &c->object.oid, "", &diffopt);
 	diffcore_std(&diffopt);
 
-	if (diff_queued_diff.nr <= max_changes) {
+	if (diffopt.num_changes <= max_changes) {
 		struct hashmap pathmap;
 		struct pathmap_hash_entry *e;
 		struct hashmap_iter iter;
diff --git a/t/t0095-bloom.sh b/t/t0095-bloom.sh
index 6defeb544f1..48a90625596 100755
--- a/t/t0095-bloom.sh
+++ b/t/t0095-bloom.sh
@@ -100,7 +100,7 @@ test_expect_success EXPENSIVE 'get bloom filter for commit with 513 changes' '
 	rm actual &&
 	rm expect &&
 	mkdir bigDir &&
-	for i in $(test_seq 0 512)
+	for i in $(test_seq 0 511)
 	do
 		echo $i >bigDir/$i
 	done &&

-- 
gitgitgadget