[PATCH 2/2] fast-import: fix 'from 0{40}' test

[Dmitry Ivankov <divanorama@gmail.com>]

parse_from_existing() has a special case for null_sha1 treating it
as a start of an orphaned branch. It is how null_sha1 parent is
treated in fast-import. For example parse_reset_branch() clears
sha1 of a branch but leaves it in a lookup table.

Looking at parse_from_existing() call sites, we can seen that it is
only called for sha1's that come from get_sha1() or an existing
object. So fast-import internals don't give it null_sha1 explicitly
and the only way for it to appear is direct '0{40}' in the input.

Don't treat null_sha1 as a magic sha1 in parse_from_existing thus
making 'from 0{40}' an invalid input. (Unless there is a commit
object having null_sha1, of course. And object with null_sha1 would
be a lot of trouble in fast-import regardless of this patch.)

Signed-off-by: Dmitry Ivankov <divanorama@gmail.com>
---
 fast-import.c          |   17 ++++++-----------
 t/t9300-fast-import.sh |    2 +-
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/fast-import.c b/fast-import.c
index 742e7da..827434a 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2488,18 +2488,13 @@ static void parse_from_commit(struct branch *b, char *buf, unsigned long size)
 
 static void parse_from_existing(struct branch *b)
 {
-	if (is_null_sha1(b->sha1)) {
-		hashclr(b->branch_tree.versions[0].sha1);
-		hashclr(b->branch_tree.versions[1].sha1);
-	} else {
-		unsigned long size;
-		char *buf;
+	unsigned long size;
+	char *buf;
 
-		buf = read_object_with_reference(b->sha1,
-			commit_type, &size, b->sha1);
-		parse_from_commit(b, buf, size);
-		free(buf);
-	}
+	buf = read_object_with_reference(b->sha1,
+		commit_type, &size, b->sha1);
+	parse_from_commit(b, buf, size);
+	free(buf);
 }
 
 static int parse_from(struct branch *b)
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 8cc3f16..0784d50 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -381,7 +381,7 @@ data 0
 
 from 0000000000000000000000000000000000000000
 INPUT_END
-test_expect_failure 'B: fail on "from 0{40}"' '
+test_expect_success 'B: fail on "from 0{40}"' '
     test_must_fail git fast-import <input
 '
 rm -f .git/objects/pack_* .git/objects/index_*
-- 
1.7.3.4