remote.c: untangle error logic in branch_get_upstream

The error-diagnosis logic in branch_get_upstream was copied straight from sha1_name.c in the previous commit. However, because we check all error cases and upfront and then later diagnose them, the logic is a bit tangled. In particular: - if branch->merge[0] is NULL, we may end up dereferencing it for an error message (in practice, it should never be NULL, so this is probably not a triggerable bug). - We may enter the code path because branch->merge[0]->dst is NULL, but we then start our error diagnosis by checking whether our local branch exists. But that is only relevant to diagnosing missing merge config, not a missing tracking ref; our diagnosis may hide the real problem. Instead, let's just use a sequence of "if" blocks to check for each error type, diagnose it, and return NULL. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

remote.c

@@ -1721,18 +1721,25 @@ const char *branch_get_upstream(struct branch *branch, struct strbuf *err)
 {
 if (!branch)
 return error_buf(err, _("HEAD does not point to a branch"));
-if (!branch->merge || !branch->merge[0] || !branch->merge[0]->dst) {
+
+if (!branch->merge || !branch->merge[0]) {
+/*
+ * no merge config; is it because the user didn't define any,
+ * or because it is not a real branch, and get_branch
+ * auto-vivified it?
+ */
 if (!ref_exists(branch->refname))
 return error_buf(err, _("no such branch: '%s'"),
  branch->name);
-if (!branch->merge)
-return error_buf(err,
- _("no upstream configured for branch '%s'"),
- branch->name);
+return error_buf(err,
+ _("no upstream configured for branch '%s'"),
+ branch->name);
+}
+
+if (!branch->merge[0]->dst)
 return error_buf(err,
  _("upstream branch '%s' not stored as a remote-tracking branch"),
  branch->merge[0]->src);
-}
 
 return branch->merge[0]->dst;
 }