Subject: [PATCH v3 7/8] pack-objects: prevent name hash version change

From: "Derrick Stolee via GitGitGadget" <[email-masked]>
Date: Fri, 20 Dec 2024 17:19:53 +0000

From: Derrick Stolee <[email-masked]>

When the --name-hash-version option is used in 'git pack-objects', it
can change from the initial assignment to when it is used based on
interactions with other arguments. Specifically, when writing or reading
bitmaps, we must force version 1 for now. This could change in the
future when the bitmap format can store a name hash version value,
indicating which was used during the writing of the packfile.

Protect the 'git pack-objects' process from getting confused by failing
with a BUG() statement if the value of the name hash version changes
between calls to pack_name_hash_fn().

Signed-off-by: Derrick Stolee <[email-masked]>
---
 builtin/pack-objects.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index b19c3665003..4d10baf7ac9 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -276,6 +276,14 @@ static void validate_name_hash_version(void)
 
 static inline uint32_t pack_name_hash_fn(const char *name)
 {
+	static int seen_version = -1;
+
+	if (seen_version < 0)
+		seen_version = name_hash_version;
+	else if (seen_version != name_hash_version)
+		BUG("name hash version changed from %d to %d mid-process",
+		    seen_version, name_hash_version);
+
 	switch (name_hash_version)
 	{
 	case 1:
-- 
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