[PATCH] archive: fix archive generation for empty trees

[Brodie Rao <brodie@sf.io>]

Prior to this change, git-archive would try to verify path arguments -
even if none were provided. It used get_pathspec("", pathspec), which
would return a pathspec of "" instead of NULL.

Then it would try to verify if the tree contained any paths matching
"". This is fine in the normal case where the tree contains anything
(every entry would match), but for an empty tree, it wouldn't match,
and you'd get this error:

  fatal: path not found:

Now, instead of "", we use a pathspec prefix of NULL. If no path
arguments were provided, get_pathspec() will return NULL, and we won't
try to verify the existence of any paths in the tree.

Signed-off-by: Brodie Rao <brodie@sf.io>
---
 archive.c           |    2 +-
 t/t5000-tar-tree.sh |   16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/archive.c b/archive.c
index 1ee837d..6e23896 100644
--- a/archive.c
+++ b/archive.c
@@ -236,7 +236,7 @@ static int path_exists(struct tree *tree, const char *path)
 static void parse_pathspec_arg(const char **pathspec,
 		struct archiver_args *ar_args)
 {
-	ar_args->pathspec = pathspec = get_pathspec("", pathspec);
+	ar_args->pathspec = pathspec = get_pathspec(NULL, pathspec);
 	if (pathspec) {
 		while (*pathspec) {
 			if (!path_exists(ar_args->tree, *pathspec))
diff --git a/t/t5000-tar-tree.sh b/t/t5000-tar-tree.sh
index 527c9e7..404786f 100755
--- a/t/t5000-tar-tree.sh
+++ b/t/t5000-tar-tree.sh
@@ -360,4 +360,20 @@ test_expect_success GZIP 'remote tar.gz can be disabled' '
 		>remote.tar.gz
 '
 
+test_expect_success \
+    'git archive with an empty tree and a prefix' \
+    'git rm -r . &&
+     git commit -m empty &&
+     git archive --format=tar --prefix=empty/ HEAD > e1.tar &&
+     "$TAR" tf e1.tar'
+
+test_expect_success \
+    'git archive with an empty tree and no prefix' \
+    'git archive --format=tar HEAD > e2.tar &&
+     test_must_fail "$TAR" tf e2.tar'
+
+test_expect_success \
+    'git archive on specific paths with an empty tree' \
+    'test_must_fail git archive --format=tar --prefix=empty/ HEAD foo'
+
 test_done
-- 
1.7.9.2