fsck: detect null sha1 in tree entries

Short of somebody happening to beat the 1 in 2^160 odds of
actually generating content that hashes to the null sha1, we
should never see this value in a tree entry. So let's have
fsck warn if it it seen.

As in the previous commit, we test both blob and submodule
entries to future-proof the test suite against the
implementation depending on connectivity to notice the
error.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 5b8ebd8..5e36cc7 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -217,4 +217,30 @@ test_expect_success 'rev-list --verify-objects with bad sha1' '
 	grep -q "error: sha1 mismatch 63ffffffffffffffffffffffffffffffffffffff" out
 '
 
+_bz='\0'
+_bz5="$_bz$_bz$_bz$_bz$_bz"
+_bz20="$_bz5$_bz5$_bz5$_bz5"
+
+test_expect_success 'fsck notices blob entry pointing to null sha1' '
+	(git init null-blob &&
+	 cd null-blob &&
+	 sha=$(printf "100644 file$_bz$_bz20" |
+	       git hash-object -w --stdin -t tree) &&
+	  git fsck 2>out &&
+	  cat out &&
+	  grep "warning.*null sha1" out
+	)
+'
+
+test_expect_success 'fsck notices submodule entry pointing to null sha1' '
+	(git init null-commit &&
+	 cd null-commit &&
+	 sha=$(printf "160000 submodule$_bz$_bz20" |
+	       git hash-object -w --stdin -t tree) &&
+	  git fsck 2>out &&
+	  cat out &&
+	  grep "warning.*null sha1" out
+	)
+'
+
 test_done