[PATCH v5 6/6] refs: make errno output explicit for refs_resolve_ref_unsafe

["Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@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>
Reviewed-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 refs/files-backend.c | 15 ++++++++-------
 refs/refs-internal.h |  8 ++++++++
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 7aafdf2ce3d..d6a7a0ee919 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -929,6 +929,7 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 	int mustexist = (old_oid && !is_null_oid(old_oid));
 	int resolve_flags = RESOLVE_REF_NO_RECURSE;
 	int resolved;
+	int resolve_errno = 0;
 
 	files_assert_main_repository(refs, "lock_ref_oid_basic");
 	assert(err);
@@ -941,10 +942,11 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 		resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;
 
 	files_ref_path(refs, &ref_file, refname);
-	resolved = !!refs_resolve_ref_unsafe(&refs->base,
-					     refname, resolve_flags,
-					     &lock->old_oid, type);
-	if (!resolved && errno == EISDIR) {
+	resolved = !!refs_resolve_ref_unsafe_with_errno(&refs->base, refname,
+							resolve_flags,
+							&lock->old_oid, type,
+							&resolve_errno);
+	if (!resolved && resolve_errno == EISDIR) {
 		/*
 		 * we are trying to lock foo but we used to
 		 * have foo/bar which now does not exist;
@@ -964,15 +966,14 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 						     &lock->old_oid, type);
 	}
 	if (!resolved) {
-		int last_errno = errno;
-		if (last_errno != ENOTDIR ||
+		if (resolve_errno != ENOTDIR ||
 		    /* in case of D/F conflict, try to generate a better error
 		     * message. If that fails, fall back to strerror(ENOTDIR).
 		     */
 		    !refs_verify_refname_available(&refs->base, refname, extras,
 						   skip, err))
 			strbuf_addf(err, "unable to resolve reference '%s': %s",
-				    refname, strerror(last_errno));
+				    refname, strerror(resolve_errno));
 
 		goto error_return;
 	}
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index bf581e70cf6..df01d5dc8df 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -153,6 +153,14 @@ int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
 		      struct object_id *oid, struct strbuf *referent,
 		      unsigned int *type, int *failure_errno);
 
+/* Like refs_resolve_ref_unsafe, but provide access to errno code that lead to a
+ * failure. */
+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);
+
 /*
  * Write an error to `err` and return a nonzero value iff the same
  * refname appears multiple times in `refnames`. `refnames` must be
-- 
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