[PATCH 7/7] rev-list: detect broken root trees

[Taylor Blau <me@ttaylorr.com>]

From: Jeff King <peff@peff.net>

When the traversal machinery sees a commit without a root tree, it
assumes that the tree was part of a BOUNDARY commit, and quietly ignores
the tree. But it could also be caused by a commit whose root tree is
broken or missing.

Instead, let's die() when we see a NULL root tree. We can differentiate
it from the BOUNDARY case by seeing if the commit was actually parsed.
This covers that case, plus future-proofs us against any others where we
might try to show an unparsed commit.

Signed-off-by: Jeff King <peff@peff.net>
---
 list-objects.c                         | 3 +++
 t/t6102-rev-list-unexpected-objects.sh | 6 ++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/list-objects.c b/list-objects.c
index bb7e61ef4b..b5651ddd5b 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -374,6 +374,9 @@ static void do_traverse(struct traversal_context *ctx)
 			struct tree *tree = get_commit_tree(commit);
 			tree->object.flags |= NOT_USER_GIVEN;
 			add_pending_tree(ctx->revs, tree);
+		} else if (commit->object.parsed) {
+			die(_("unable to load root tree for commit %s"),
+			      oid_to_hex(&commit->object.oid));
 		}
 		ctx->show_commit(commit, ctx->show_data);
 
diff --git a/t/t6102-rev-list-unexpected-objects.sh b/t/t6102-rev-list-unexpected-objects.sh
index c8d4b31f8f..98f5cffbb6 100755
--- a/t/t6102-rev-list-unexpected-objects.sh
+++ b/t/t6102-rev-list-unexpected-objects.sh
@@ -68,8 +68,10 @@ test_expect_success 'traverse unexpected non-tree root (lone)' '
 	test_must_fail git rev-list --objects $broken_commit
 '
 
-test_expect_failure 'traverse unexpected non-tree root (seen)' '
-	test_must_fail git rev-list --objects $blob $broken_commit
+test_expect_success 'traverse unexpected non-tree root (seen)' '
+	test_must_fail git rev-list --objects $blob $broken_commit \
+		>output 2>&1 &&
+	test_i18ngrep "not a tree" output
 '
 
 test_expect_success 'setup unexpected non-commit tag' '
-- 
2.21.0.203.g358da99528