git-clone.sh: properly configure remote even if remote's head is dangling

When cloning a remote repository which's HEAD refers to a nonexistent
ref, git-clone cloned all existing refs, but failed to write the
configuration for 'remote'.  Now it detects the dangling remote HEAD,
refuses to checkout any local branch since HEAD refers to nowhere, but
properly writes the configuration for 'remote', so that subsequent
'git fetch's don't fail.

The problem was reported by Daniel Jacobowitz through
 http://bugs.debian.org/466581Signed-off-by: NGerrit Pape <pape@smarden.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-clone.sh

@@ -409,11 +409,12 @@ else
 	cd "$D" || exit
 fi
 
-if test -z "$bare" && test -f "$GIT_DIR/REMOTE_HEAD"
+if test -z "$bare"
 then
 	# a non-bare repository is always in separate-remote layout
 	remote_top="refs/remotes/$origin"
-	head_sha1=`cat "$GIT_DIR/REMOTE_HEAD"`
+	head_sha1=
+	test ! -r "$GIT_DIR/REMOTE_HEAD" || head_sha1=`cat "$GIT_DIR/REMOTE_HEAD"`
 	case "$head_sha1" in
 	'ref: refs/'*)
 		# Uh-oh, the remote told us (http transport done against
@@ -470,9 +471,16 @@ then
 		git config branch."$head_points_at".merge "refs/heads/$head_points_at"
 		;;
 	'')
-		# Source had detached HEAD pointing nowhere
-		git update-ref --no-deref HEAD "$head_sha1" &&
-		rm -f "refs/remotes/$origin/HEAD"
+		if test -z "$head_sha1"
+		then
+			# Source had nonexistent ref in HEAD
+			echo >&2 "Warning: Remote HEAD refers to nonexistent ref, unable to checkout."
+			no_checkout=t
+		else
+			# Source had detached HEAD pointing nowhere
+			git update-ref --no-deref HEAD "$head_sha1" &&
+			rm -f "refs/remotes/$origin/HEAD"
+		fi
 		;;
 	esac
 

t/t5701-clone-local.sh

@@ -63,4 +63,12 @@ test_expect_success 'Even without -l, local will make a hardlink' '
 	test 0 = $copied
 '
 
+test_expect_success 'local clone of repo with nonexistent ref in HEAD' '
+	cd "$D" &&
+	echo "ref: refs/heads/nonexistent" > a.git/HEAD &&
+	git clone a d &&
+	cd d &&
+	git fetch &&
+	test ! -e .git/refs/remotes/origin/HEAD'
+
 test_done