Merge branch 'jk/set-upstream-error-cases'

The handing by "git branch --set-upstream-to" against various forms
of errorneous inputs were suboptimal.

* jk/set-upstream-error-cases:
  branch: give advice when tracking start-point is missing
  branch: mention start_name in set-upstream error messages
  branch: improve error message for missing --set-upstream-to ref
  branch: factor out "upstream is not a branch" error messages
  t3200: test --set-upstream-to with bogus refs

advice.c

@@ -13,6 +13,7 @@ int advice_commit_before_merge = 1;
 int advice_resolve_conflict = 1;
 int advice_implicit_identity = 1;
 int advice_detached_head = 1;
+int advice_set_upstream_failure = 1;
 
 static struct {
 	const char *name;
@@ -31,6 +32,7 @@ static struct {
 	{ "resolveconflict", &advice_resolve_conflict },
 	{ "implicitidentity", &advice_implicit_identity },
 	{ "detachedhead", &advice_detached_head },
+	{ "setupstreamfailure", &advice_set_upstream_failure },
 
 	/* make this an alias for backward compatibility */
 	{ "pushnonfastforward", &advice_push_update_rejected }

advice.h

@@ -16,6 +16,7 @@ extern int advice_commit_before_merge;
 extern int advice_resolve_conflict;
 extern int advice_implicit_identity;
 extern int advice_detached_head;
+extern int advice_set_upstream_failure;
 
 int git_default_advice_config(const char *var, const char *value);
 void advise(const char *advice, ...);

branch.c

@@ -197,6 +197,20 @@ int validate_new_branchname(const char *name, struct strbuf *ref,
 	return 1;
 }
 
+static const char upstream_not_branch[] =
+N_("Cannot setup tracking information; starting point '%s' is not a branch.");
+static const char upstream_missing[] =
+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,
 		   int force, int reflog, int clobber_head,
@@ -224,21 +238,30 @@ void create_branch(const char *head,
 	}
 
 	real_ref = NULL;
-	if (get_sha1(start_name, sha1))
+	if (get_sha1(start_name, sha1)) {
+		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);
+	}
 
 	switch (dwim_ref(start_name, strlen(start_name), sha1, &real_ref)) {
 	case 0:
 		/* Not branching from any existing branch */
 		if (explicit_tracking)
-			die("Cannot setup tracking information; starting point is not a branch.");
+			die(_(upstream_not_branch), start_name);
 		break;
 	case 1:
 		/* Unique completion -- good, only if it is a real branch */
 		if (prefixcmp(real_ref, "refs/heads/") &&
 		    prefixcmp(real_ref, "refs/remotes/")) {
 			if (explicit_tracking)
-				die("Cannot setup tracking information; starting point is not a branch.");
+				die(_(upstream_not_branch), start_name);
 			else
 				real_ref = NULL;
 		}

t/t3200-branch.sh

@@ -409,6 +409,18 @@ test_expect_success '--set-upstream-to fails on detached HEAD' '
 	git checkout -
 '
 
+test_expect_success '--set-upstream-to fails on a missing dst branch' '
+	test_must_fail git branch --set-upstream-to master does-not-exist
+'
+
+test_expect_success '--set-upstream-to fails on a missing src branch' '
+	test_must_fail git branch --set-upstream-to does-not-exist master
+'
+
+test_expect_success '--set-upstream-to fails on a non-ref' '
+	test_must_fail git branch --set-upstream-to HEAD^{}
+'
+
 test_expect_success 'use --set-upstream-to modify HEAD' '
 	test_config branch.master.remote foo &&
 	test_config branch.master.merge foo &&