branch: give advice when tracking start-point is missing

If the user requests to --set-upstream-to a branch that does
not exist, then either:

  1. It was a typo.

  2. They thought the branch should exist.

In case (1), there is not much we can do beyond showing the
name we tried to use. For case (2), though, we can help to
guide them through common workflows.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/branch.c b/branch.c
index d6f40015d..6ae6a4c32 100644
--- a/branch.c
+++ b/branch.c
@@ -200,7 +200,16 @@ int validate_new_branchname(const char *name, struct strbuf *ref,
 static const char upstream_not_branch[] =
 N_("Cannot setup tracking information; starting point '%s' is not a branch.");
 static const char upstream_missing[] =
-N_("Cannot setup tracking information; starting point '%s' does not exist");
+N_("the requested upstream branch '%s' does not exist");
+static const char upstream_advice[] =
+N_("\n"
+"If you are planning on basing your work on an upstream\n"
+"branch that already exists at the remote, you may need to\n"
+"run \"git fetch\" to retrieve it.\n"
+"\n"
+"If you are planning to push out a new local branch that\n"
+"will track its remote counterpart, you may want to use\n"
+"\"git push -u\" to set the upstream config as you push.");
 
 void create_branch(const char *head,
 		   const char *name, const char *start_name,
@@ -230,8 +239,14 @@ void create_branch(const char *head,
 
 	real_ref = NULL;
 	if (get_sha1(start_name, sha1)) {
-		if (explicit_tracking)
+		if (explicit_tracking) {
+			if (advice_set_upstream_failure) {
+				error(_(upstream_missing), start_name);
+				advise(_(upstream_advice));
+				exit(1);
+			}
 			die(_(upstream_missing), start_name);
+		}
 		die("Not a valid object name: '%s'.", start_name);
 	}