[PATCH v9 7/7] refs: make errno output explicit for refs_resolve_ref_unsafe

[Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>]

From: Han-Wen Nienhuys <hanwen@xxxxxxxxxx>

This introduces refs_resolve_ref_unsafe_with_errno(), which makes the API
contract for the errno output explicit. The implementation still relies on
the global errno variable to ensure no side effects of this refactoring.

lock_ref_oid_basic() in files-backend.c is the only caller of refs_resolve_ref()
that needs error information to make logic decisions, so update that caller

Signed-off-by: Han-Wen Nienhuys <hanwen@xxxxxxxxxx>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 refs.c               |  2 +-
 refs.h               | 11 +++++++++++
 refs/files-backend.c | 10 ++++++----
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/refs.c b/refs.c
index b31dbdd0fa2..9497b51e0a1 100644
--- a/refs.c
+++ b/refs.c
@@ -1688,7 +1688,7 @@ int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
 					   type, failure_errno);
 }
 
-static const char *refs_resolve_ref_unsafe_with_errno(struct ref_store *refs,
+const char *refs_resolve_ref_unsafe_with_errno(struct ref_store *refs,
 					       const char *refname,
 					       int resolve_flags,
 					       struct object_id *oid,
diff --git a/refs.h b/refs.h
index c009707438d..ba09ba0687b 100644
--- a/refs.h
+++ b/refs.h
@@ -68,6 +68,17 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 				    int resolve_flags,
 				    struct object_id *oid,
 				    int *flags);
+/**
+ * refs_resolve_ref_unsafe_with_errno() is like
+ * refs_resolve_ref_unsafe(), but provide access to errno code that
+ * lead to a failure. We guarantee that errno is set to a meaningful
+ * value on non-zero return.
+ */
+const char *refs_resolve_ref_unsafe_with_errno(struct ref_store *refs,
+					       const char *refname,
+					       int resolve_flags,
+					       struct object_id *oid,
+					       int *flags, int *failure_errno);
 const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
 			       struct object_id *oid, int *flags);
 
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 746831c86cb..68182296c1b 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1001,6 +1001,7 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 {
 	struct strbuf ref_file = STRBUF_INIT;
 	struct ref_lock *lock;
+	int resolve_errno = 0;
 
 	files_assert_main_repository(refs, "lock_ref_oid_basic");
 	assert(err);
@@ -1008,13 +1009,14 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 	CALLOC_ARRAY(lock, 1);
 
 	files_ref_path(refs, &ref_file, refname);
-	if (!refs_resolve_ref_unsafe(&refs->base, refname,
-				     RESOLVE_REF_NO_RECURSE,
-				     &lock->old_oid, type)) {
+	if (!refs_resolve_ref_unsafe_with_errno(&refs->base, refname,
+						RESOLVE_REF_NO_RECURSE,
+						&lock->old_oid, type,
+						&resolve_errno)) {
 		if (!refs_verify_refname_available(&refs->base, refname,
 						   NULL, NULL, err))
 			strbuf_addf(err, "unable to resolve reference '%s': %s",
-				    refname, strerror(errno));
+				    refname, strerror(resolve_errno));
 
 		goto error_return;
 	}
-- 
2.32.0.874.ge7a9d58bfcf