update_ref(): improve documentation

Add a docstring for update_ref(), emphasizing its similarity to
ref_transaction_update(). Rename its parameters to match those of
ref_transaction_update().

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -3738,8 +3738,8 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 				      flags, NULL, err);
 }
 
-int update_ref(const char *action, const char *refname,
-	       const unsigned char *sha1, const unsigned char *oldval,
+int update_ref(const char *msg, const char *refname,
+	       const unsigned char *new_sha1, const unsigned char *old_sha1,
 	       unsigned int flags, enum action_on_err onerr)
 {
 	struct ref_transaction *t;
@@ -3747,8 +3747,8 @@ int update_ref(const char *action, const char *refname,
 
 	t = ref_transaction_begin(&err);
 	if (!t ||
-	    ref_transaction_update(t, refname, sha1, oldval,
-				   flags, action, &err) ||
+	    ref_transaction_update(t, refname, new_sha1, old_sha1,
+				   flags, msg, &err) ||
 	    ref_transaction_commit(t, &err)) {
 		const char *str = "update_ref failed for ref '%s': %s";
 

refs.h

@@ -344,9 +344,16 @@ int ref_transaction_commit(struct ref_transaction *transaction,
  */
 void ref_transaction_free(struct ref_transaction *transaction);
 
-/** Lock a ref and then write its file */
-int update_ref(const char *action, const char *refname,
-	       const unsigned char *sha1, const unsigned char *oldval,
+/**
+ * Lock, update, and unlock a single reference. This function
+ * basically does a transaction containing a single call to
+ * ref_transaction_update(). The parameters to this function have the
+ * same meaning as the corresponding parameters to
+ * ref_transaction_update(). Handle errors as requested by the `onerr`
+ * argument.
+ */
+int update_ref(const char *msg, const char *refname,
+	       const unsigned char *new_sha1, const unsigned char *old_sha1,
 	       unsigned int flags, enum action_on_err onerr);
 
 extern int parse_hide_refs_config(const char *var, const char *value, const char *);