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List:       git
Subject:    [RFC PATCH 6/6] commit-graph: revert to odb on missing parents
From:       Derrick Stolee <dstolee () microsoft ! com>
Date:       2018-05-31 17:41:20
Message-ID: 20180531174024.124488-7-dstolee () microsoft ! com
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The commit-graph format includes a way to specify a parent is
"missing" from the commit-graph (i.e. we do not have a record of
that parent in our list of object IDs, and hence cannot provide
a graph position). For mose cases, this does not occur due to
the close_reachable() method adding all reachable commits. However,
in a shallow clone, we will try to record the parents of a commit
on the shallow boundary, but the parents are not in the repository.

The GRAPH_PARENT_MISSING value that is stored in the format is
purposeful, especially for future plans to make the commit-graph file
incremental or transporting sections of a commit-graph file across
the network.

In the meantime, check if a commit has a missing parent while filling
its details from the commit-graph. If a parent is missing, still
assign the generation number and graph position for that item, but
report that the commit-graph failed to fill the contents. Then the
caller is responsible for filling the rest of the data from a commit
buffer.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 commit-graph.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/commit-graph.c b/commit-graph.c
index 80e377b90f..3e33d061fe 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -278,17 +278,44 @@ static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uin
 	struct commit_list **pptr;
 	const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
 
-	item->object.parsed = 1;
+	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
 	item->graph_pos = pos;
 
+	/*
+	 * If we have any edges marked as GRAPH_PARENT_MISSING, we must not parse any
+	 * more of this object and leave it to the commit buffer to parse.
+	 */
+	edge_value = get_be32(commit_data + g->hash_len);
+	if (edge_value == GRAPH_PARENT_MISSING)
+		return 0;
+	if (edge_value == GRAPH_PARENT_NONE)
+		goto continue_parsing;
+
+	edge_value = get_be32(commit_data + g->hash_len + 4);
+	if (edge_value == GRAPH_PARENT_MISSING)
+		return 0;
+	if (edge_value == GRAPH_PARENT_NONE)
+		goto continue_parsing;
+	if (!(edge_value & GRAPH_OCTOPUS_EDGES_NEEDED))
+		goto continue_parsing;
+
+	parent_data_ptr = (uint32_t*)(g->chunk_large_edges +
+			  4 * (uint64_t)(edge_value & GRAPH_EDGE_LAST_MASK));
+	do {
+		edge_value = get_be32(parent_data_ptr);
+		if (edge_value == GRAPH_PARENT_MISSING)
+			return 0;
+		parent_data_ptr++;
+	} while (!(edge_value & GRAPH_LAST_EDGE));
+	
+continue_parsing:
+	item->object.parsed = 1;
 	item->maybe_tree = NULL;
 
 	date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
 	date_low = get_be32(commit_data + g->hash_len + 12);
 	item->date = (timestamp_t)((date_high << 32) | date_low);
 
-	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
-
 	pptr = &item->parents;
 
 	edge_value = get_be32(commit_data + g->hash_len);
-- 
2.16.2.338.gcfe06ae955

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