[RFD/PATCH 4/5] branch.c: Look up refspecs to validate tracking branches

[Johan Herland <johan@herland.net>]

The current code for validating tracking branches (e.g. the argument to the
-t/--track option) hardcodes refs/heads/* and refs/remotes/* as the potential
locations for tracking branches. This works well with the conventional
refspecs created by "git clone" or "git remote add", but does not work if the
user tweaks the refspecs to place remote-tracking branches outside
refs/remotes/*.

This patch adds explicit checking of the refspecs for each remote to determine
whether a candidate tracking branch is indeed a valid remote-tracking branch,
even if placed outside refs/heads/* and refs/remotes/*.

This new check is added as a fallback after checking for match against
refs/heads/* and refs/remotes/*, so the code will not be run in the common
case.

This patch also fixes the last remaining test failure in t2024-checkout-dwim.

Signed-off-by: Johan Herland <johan@herland.net>
---
 branch.c                 | 18 +++++++++++++++++-
 t/t2024-checkout-dwim.sh |  2 +-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/branch.c b/branch.c
index 6ae6a4c..c9f9dec 100644
--- a/branch.c
+++ b/branch.c
@@ -197,6 +197,21 @@ int validate_new_branchname(const char *name, struct strbuf *ref,
 	return 1;
 }
 
+static int check_tracking_branch(struct remote *remote, void *cb_data)
+{
+	char *tracking_branch = cb_data;
+	struct refspec query;
+	memset(&query, 0, sizeof(struct refspec));
+	query.dst = tracking_branch;
+	return !(remote_find_tracking(remote, &query) ||
+		 prefixcmp(query.src, "refs/heads/"));
+}
+
+static int validate_remote_tracking_branch(char *ref)
+{
+	return !for_each_remote(check_tracking_branch, ref);
+}
+
 static const char upstream_not_branch[] =
 N_("Cannot setup tracking information; starting point '%s' is not a branch.");
 static const char upstream_missing[] =
@@ -259,7 +274,8 @@ void create_branch(const char *head,
 	case 1:
 		/* Unique completion -- good, only if it is a real branch */
 		if (prefixcmp(real_ref, "refs/heads/") &&
-		    prefixcmp(real_ref, "refs/remotes/")) {
+		    prefixcmp(real_ref, "refs/remotes/") &&
+		    validate_remote_tracking_branch(real_ref)) {
 			if (explicit_tracking)
 				die(_(upstream_not_branch), start_name);
 			else
diff --git a/t/t2024-checkout-dwim.sh b/t/t2024-checkout-dwim.sh
index fc6edc9..a8f0a90 100755
--- a/t/t2024-checkout-dwim.sh
+++ b/t/t2024-checkout-dwim.sh
@@ -108,7 +108,7 @@ test_expect_success 'checkout of branch from a single remote succeeds #3' '
 	test_tracking_branch spam repo_c refs/remotes/extra_dir/repo_c/extra_dir/spam
 '
 
-test_expect_failure 'checkout of branch from a single remote succeeds #4' '
+test_expect_success 'checkout of branch from a single remote succeeds #4' '
 	git checkout eggs &&
 	test_tracking_branch eggs repo_d refs/repo_d/eggs
 '
-- 
1.8.1.3.704.g33f7d4f