[PATCH v2 6/7] reflog_expire(): ignore --updateref for symbolic references

[Michael Haggerty <mhagger@alum.mit.edu>]

If we are expiring reflog entries for a symbolic reference, then how
should --updateref be handled if the newest reflog entry is expired?

Option 1: Update the referred-to reference. (This is what the current
code does.) This doesn't make sense, because the referred-to reference
has its own reflog, which hasn't been rewritten.

Option 2: Update the symbolic reference itself (as in, REF_NODEREF).
This would convert the symbolic reference into a non-symbolic
reference (e.g., detaching HEAD), which is surely not what a user
would expect.

Option 3: Error out. This is plausible, but it would make the
following usage impossible:

    git reflog expire ... --updateref --all

Option 4: Ignore --updateref for symbolic references.

We choose to implement option 4.

Note: another problem in this code will be fixed in a moment.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 Documentation/git-reflog.txt |  3 ++-
 refs.c                       | 15 ++++++++++++---
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-reflog.txt b/Documentation/git-reflog.txt
index 3af9422..d49db7c 100644
--- a/Documentation/git-reflog.txt
+++ b/Documentation/git-reflog.txt
@@ -89,7 +89,8 @@ Options for `expire` and/or `delete`
 
 --updateref::
 	Update the reference to the value of the top reflog entry (i.e.
-	<ref>@\{0\}) if the previous top entry was pruned.
+	<ref>@\{0\}) if the previous top entry was pruned.  (This
+	option is ignored for symbolic references.)
 
 --rewrite::
 	While expiring or deleting, adjust each reflog entry's "old"
diff --git a/refs.c b/refs.c
index f2e9883..bd47d23 100644
--- a/refs.c
+++ b/refs.c
@@ -4026,6 +4026,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	struct ref_lock *lock;
 	char *log_file;
 	int status = 0;
+	int type;
 
 	memset(&cb, 0, sizeof(cb));
 	cb.flags = flags;
@@ -4037,7 +4038,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	 * reference itself, plus we might need to update the
 	 * reference if --updateref was specified:
 	 */
-	lock = lock_ref_sha1_basic(refname, sha1, NULL, 0, NULL);
+	lock = lock_ref_sha1_basic(refname, sha1, NULL, 0, &type);
 	if (!lock)
 		return error("cannot lock ref '%s'", refname);
 	if (!reflog_exists(refname)) {
@@ -4074,10 +4075,18 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	(*cleanup_fn)(cb.policy_cb);
 
 	if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
+		/*
+		 * It doesn't make sense to adjust a reference pointed
+		 * to by a symbolic ref based on expiring entries in
+		 * the symbolic reference's reflog.
+		 */
+		int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
+			!(type & REF_ISSYMREF);
+
 		if (close_lock_file(&reflog_lock)) {
 			status |= error("couldn't write %s: %s", log_file,
 					strerror(errno));
-		} else if ((flags & EXPIRE_REFLOGS_UPDATE_REF) &&
+		} else if (update &&
 			(write_in_full(lock->lock_fd,
 				sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
 			 write_str_in_full(lock->lock_fd, "\n") != 1 ||
@@ -4088,7 +4097,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 		} else if (commit_lock_file(&reflog_lock)) {
 			status |= error("unable to commit reflog '%s' (%s)",
 					log_file, strerror(errno));
-		} else if ((flags & EXPIRE_REFLOGS_UPDATE_REF) && commit_ref(lock)) {
+		} else if (update && commit_ref(lock)) {
 			status |= error("couldn't set %s", lock->ref_name);
 		}
 	}
-- 
2.1.4