contrib/subtree: Handle '--prefix' argument with a slash appended

'git subtree merge' will fail if the argument of '--prefix' has a slash
appended.

Signed-off-by: Techlive Zheng <techlivezheng@gmail.com>
Signed-off-by: David A. Greene <greened@obbligato.org>
Signed-off-by: Jeff King <peff@peff.net>

contrib/subtree/git-subtree.sh

@@ -90,7 +90,7 @@ while [ $# -gt 0 ]; do
 		--annotate) annotate="$1"; shift ;;
 		--no-annotate) annotate= ;;
 		-b) branch="$1"; shift ;;
-		-P) prefix="$1"; shift ;;
+		-P) prefix="${1%/}"; shift ;;
 		-m) message="$1"; shift ;;
 		--no-prefix) prefix= ;;
 		--onto) onto="$1"; shift ;;

contrib/subtree/t/t7900-subtree.sh

@@ -257,6 +257,26 @@ test_expect_success 'merge the added subproj again, should do nothing' '
 	)
 '
 
+next_test
+test_expect_success 'merge new subproj history into subdir/ with a slash appended to the argument of --prefix' '
+	test_create_repo "$test_count" &&
+	test_create_repo "$test_count/subproj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/subproj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./subproj master &&
+		git subtree add --prefix=subdir/ FETCH_HEAD
+	) &&
+	test_create_commit "$test_count/subproj" sub2 &&
+	(
+		cd "$test_count" &&
+		git fetch ./subproj master &&
+		git subtree merge --prefix=subdir/ FETCH_HEAD &&
+		check_equal "$(last_commit_message)" "Merge commit '\''$(git rev-parse FETCH_HEAD)'\''"
+	)
+'
+
 #
 # Tests for 'git subtree split'
 #