[PATCH 4/8] refs: make errno output explicit for refs_resolve_ref_unsafe

["Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com>]

From: Han-Wen Nienhuys <hanwen@google.com>

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.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
---
 refs.c               | 12 ++++++++++++
 refs.h               |  1 +
 refs/files-backend.c | 19 ++++++++++---------
 refs/refs-internal.h |  8 ++++++++
 4 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/refs.c b/refs.c
index 43e2ad6b612a..e8ce88040b3e 100644
--- a/refs.c
+++ b/refs.c
@@ -1780,6 +1780,18 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 	return NULL;
 }
 
+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 *result = refs_resolve_ref_unsafe(refs, refname,
+						     resolve_flags, oid, flags);
+	*failure_errno = errno;
+	return result;
+}
+
 /* backend functions */
 int refs_init_db(struct strbuf *err)
 {
diff --git a/refs.h b/refs.h
index 48970dfc7e0f..ede405ac3874 100644
--- a/refs.h
+++ b/refs.h
@@ -68,6 +68,7 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 				    int resolve_flags,
 				    struct object_id *oid,
 				    int *flags);
+
 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 efe493ca1425..3ab09871db5e 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -924,6 +924,7 @@ 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;
 
 	files_assert_main_repository(refs, "lock_ref_oid_basic");
 	assert(err);
@@ -936,10 +937,11 @@ 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;
@@ -959,12 +961,11 @@ 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 ||
-		    !refs_verify_refname_available(&refs->base, refname,
-						   extras, skip, err))
+		if (resolve_errno != 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 ac8a14086724..b9f713b5acd6 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);
 
+/* 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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