commit-graph: writing missing parents is a BUG

When writing a commit-graph, we write GRAPH_MISSING_PARENT if the
parent's object id does not appear in the list of commits to be
written into the commit-graph. This was done as the initial design
allowed commits to have missing parents, but the final version
requires the commit-graph to be closed under reachability. Thus,
this GRAPH_MISSING_PARENT value should never be written.

However, there are reasons why it could be written! These range
from a bug in the reachable-closure code to a memory error causing
the binary search into the list of object ids to fail. In either
case, we should fail fast and avoid writing the commit-graph file
with bad data.

Remove the GRAPH_MISSING_PARENT constant in favor of the constant
GRAPH_EDGE_LAST_MASK, which has the same value.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit-graph.c b/commit-graph.c
index 40c855f1855595fbf5b285008d3c829e6a2f41eb..c14ada6918ac9b0fc847bcb1b7c2cadf3d26383a 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -34,7 +34,6 @@
 #define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1
 
 #define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000
-#define GRAPH_PARENT_MISSING 0x7fffffff
 #define GRAPH_EDGE_LAST_MASK 0x7fffffff
 #define GRAPH_PARENT_NONE 0x70000000
 
@@ -496,7 +495,9 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
                                              commit_to_sha1);
 
                        if (edge_value < 0)
-                               edge_value = GRAPH_PARENT_MISSING;
+                               BUG("missing parent %s for commit %s",
+                                   oid_to_hex(&parent->item->object.oid),
+                                   oid_to_hex(&(*list)->object.oid));
                }
 
                hashwrite_be32(f, edge_value);
@@ -514,7 +515,9 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
                                              nr_commits,
                                              commit_to_sha1);
                        if (edge_value < 0)
-                               edge_value = GRAPH_PARENT_MISSING;
+                               BUG("missing parent %s for commit %s",
+                                   oid_to_hex(&parent->item->object.oid),
+                                   oid_to_hex(&(*list)->object.oid));
                }
 
                hashwrite_be32(f, edge_value);
@@ -567,7 +570,9 @@ static void write_graph_chunk_large_edges(struct hashfile *f,
                                                  commit_to_sha1);
 
                        if (edge_value < 0)
-                               edge_value = GRAPH_PARENT_MISSING;
+                               BUG("missing parent %s for commit %s",
+                                   oid_to_hex(&parent->item->object.oid),
+                                   oid_to_hex(&(*list)->object.oid));
                        else if (!parent->next)
                                edge_value |= GRAPH_LAST_EDGE;
 
@@ -864,7 +869,7 @@ void write_commit_graph(const char *obj_dir,
                        count_distinct++;
        }
 
-       if (count_distinct >= GRAPH_PARENT_MISSING)
+       if (count_distinct >= GRAPH_EDGE_LAST_MASK)
                die(_("the commit graph format cannot write %d commits"), count_distinct);
 
        commits.nr = 0;
@@ -891,7 +896,7 @@ void write_commit_graph(const char *obj_dir,
        }
        num_chunks = num_extra_edges ? 4 : 3;
 
-       if (commits.nr >= GRAPH_PARENT_MISSING)
+       if (commits.nr >= GRAPH_EDGE_LAST_MASK)
                die(_("too many commits to write graph"));
 
        compute_generation_numbers(&commits, report_progress);