[PATCH] refs: don't clear oid before read_raw_ref in the debug ref backend

[PATCH] refs: don't clear oid before read_raw_ref in the debug ref backend

[Xinyu Ruan via GitGitGadget]

From: Xinyu Ruan <r200981113@gmail.com>

The debug_read_raw_ref function clears the oid to null_oid before
calling read_raw_ref, which causes the oid to be lost even when
read_raw_ref successfully reads the reference. This leads to failures
when executing commands like "git branch new_branch <commit_id>" with
GIT_TRACE_REFS=1, as the command cannot find a valid branch point
because the oid is null.

Signed-off-by: Xinyu Ruan <r200981113@gmail.com>
---
    refs: don't clear oid before read_raw_ref in the debug ref backend

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2089%2FRuanXinyu%2Fref-debug-disable-clear-oid-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2089/RuanXinyu/ref-debug-disable-clear-oid-v1
Pull-Request: https://github.com/git/git/pull/2089

 refs/debug.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/refs/debug.c b/refs/debug.c
index 697adbd0dc..c8dde3558d 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -227,7 +227,6 @@ static int debug_read_raw_ref(struct ref_store *ref_store, const char *refname,
 	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
 	int res = 0;
 
-	oidcpy(oid, null_oid(ref_store->repo->hash_algo));
 	res = drefs->refs->be->read_raw_ref(drefs->refs, refname, oid, referent,
 					    type, failure_errno);
 

base-commit: a99f379adf116d53eb11957af5bab5214915f91d
-- 
gitgitgadget

Re: [PATCH] refs: don't clear oid before read_raw_ref in the debug ref backend

[Patrick Steinhardt]

On Fri, Oct 31, 2025 at 03:37:05AM +0000, Xinyu Ruan via GitGitGadget wrote:
> From: Xinyu Ruan <r200981113@gmail.com>
> 
> The debug_read_raw_ref function clears the oid to null_oid before
> calling read_raw_ref, which causes the oid to be lost even when
> read_raw_ref successfully reads the reference.

This sentence doesn't quite make sense to me. If `read_raw_ref()`
succeeds, wouldn't we expect that the OID was set to the target's object
ID anyway? So why does it hurt to set the object ID to the null ID if
it's going to get rewritten anyway?

Another question is why we were setting it to the null OID in the first
place. Ideally, this should be discussed in the commit message.

> This leads to failures
> when executing commands like "git branch new_branch <commit_id>" with
> GIT_TRACE_REFS=1, as the command cannot find a valid branch point
> because the oid is null.

This smells like an issue that can be be demonstrated via a unit test.
Right now though we got zero testing for `GIT_TRACE_REFS` in our test
suite. Maybe this could be used as a starting point for a new test suite
"t0620-ref-debug.sh" that exercises the different callbacks?

Thanks!

Patrick