refs/files-backend: stop setting errno from lock_ref_oid_basic

refs/files-backend.c::lock_ref_oid_basic() tries to signal how it failed
to its callers using errno.

It is safe to stop setting errno here, because the callers of this
file-scope static function are

* files_copy_or_rename_ref()
* files_create_symref()
* files_reflog_expire()

None of them looks at errno after seeing a negative return from
lock_ref_oid_basic() to make any decision, and no caller of these three
functions looks at errno after they signal a failure by returning a
negative value. In particular,

* files_copy_or_rename_ref() - here, calls are followed by error()
(which performs I/O) or write_ref_to_lockfile() (which calls
parse_object() which may perform I/O)

* files_create_symref() - here, calls are followed by error() or
create_symref_locked() (which performs I/O and does not inspect
errno)

* files_reflog_expire() - here, calls are followed by error() or
refs_reflog_exists() (which calls a function in a vtable that is not
documented to use and/or preserve errno)

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 950f9738ae0ca13476a2ce1c573ef7f16a14df79..c1794dcd295f214d3791050daff336ab0be21d5b 100644 (file)
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -982,7 +982,6 @@ static int create_reflock(const char *path, void *cb)
 
 /*
  * Locks a ref returning the lock on success and NULL on failure.
- * On failure errno is set to something meaningful.
  */
 static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
                                           const char *refname, int *type,
@@ -990,7 +989,6 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 {
        struct strbuf ref_file = STRBUF_INIT;
        struct ref_lock *lock;
-       int last_errno = 0;
 
        files_assert_main_repository(refs, "lock_ref_oid_basic");
        assert(err);
@@ -1001,11 +999,10 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
        if (!refs_resolve_ref_unsafe(&refs->base, refname,
                                     RESOLVE_REF_NO_RECURSE,
                                     &lock->old_oid, type)) {
-               last_errno = errno;
                if (!refs_verify_refname_available(&refs->base, refname,
                                                   NULL, NULL, err))
                        strbuf_addf(err, "unable to resolve reference '%s': %s",
-                                   refname, strerror(last_errno));
+                                   refname, strerror(errno));
 
                goto error_return;
        }
@@ -1018,15 +1015,12 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
         */
        if (is_null_oid(&lock->old_oid) &&
            refs_verify_refname_available(refs->packed_ref_store, refname,
-                                         NULL, NULL, err)) {
-               last_errno = ENOTDIR;
+                                         NULL, NULL, err))
                goto error_return;
-       }
 
        lock->ref_name = xstrdup(refname);
 
        if (raceproof_create_file(ref_file.buf, create_reflock, &lock->lk)) {
-               last_errno = errno;
                unable_to_lock_message(ref_file.buf, errno, err);
                goto error_return;
        }
@@ -1043,7 +1037,6 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 
  out:
        strbuf_release(&ref_file);
-       errno = last_errno;
        return lock;
 }