[RFC PATCH 1/1] commit-graph.c: die on un-parseable commits

[Taylor Blau <me@ttaylorr.com>]

When we write a commit graph chunk, we process a given list of 'struct
commit *'s and parse out the parent(s) and tree OID in order to write
out its information.

We do this by calling 'parse_commit_no_graph', and then checking the
result of 'get_commit_tree_oid' to write the tree OID. This process
assumes that 'parse_commit_no_graph' parses the commit successfully.
When this isn't the case, 'get_commit_tree_oid(*list)' may return NULL,
in which case trying to '->hash' it causes a SIGSEGV.

Instead, teach 'write_graph_chunk_data' to stop when a commit isn't able
to be parsed, at the peril of failing to write a commit-graph.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 commit-graph.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/commit-graph.c b/commit-graph.c
index f2888c203b..6aa6998ecd 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -843,7 +843,9 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 		uint32_t packedDate[2];
 		display_progress(ctx->progress, ++ctx->progress_cnt);
 
-		parse_commit_no_graph(*list);
+		if (parse_commit_no_graph(*list))
+			die(_("unable to parse commit %s"),
+				oid_to_hex(&(*list)->object.oid));
 		hashwrite(f, get_commit_tree_oid(*list)->hash, hash_len);
 
 		parent = (*list)->parents;
-- 
2.22.0