commit-graph: introduce `repo_find_commit_pos_in_graph()`

Low-level callers in systems that are adjacent to the commit-graph (like
the changed-path Bloom filter code) could benefit from being able to
call a function like `parse_commit_in_graph()` without modifying the
corresponding commit slab data.

This is useful in contexts where that slab data is being used to prepare
for an upcoming commit-graph write, where Git must be careful to avoid
clobbering any of that data during a read operation.

Introduce a low-level variant of `parse_commit_in_graph()` which returns
the graph position of a given commit only, without modifying any of the
slab data.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/commit-graph.h b/commit-graph.h
index 2e3ac35237..f23b9e9026 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -41,6 +41,21 @@ int open_commit_graph(const char *graph_file, int *fd, struct stat *st);
 int parse_commit_in_graph(struct repository *r, struct commit *item);
 
 /*
+ * Fills `*pos` with the graph position of `c`, and returns 1 if `c` is
+ * found in the commit-graph belonging to `r`, or 0 otherwise.
+ * Initializes the commit-graph belonging to `r` if it hasn't been
+ * already.
+ *
+ * Note: this is a low-level helper that does not alter any slab data
+ * associated with `c`. Useful in circumstances where the slab data is
+ * already being modified (e.g., writing the commit-graph itself).
+ *
+ * In most cases, callers should use `parse_commit_in_graph()` instead.
+ */
+int repo_find_commit_pos_in_graph(struct repository *r, struct commit *c,
+				  uint32_t *pos);
+
+/*
  * Look up the given commit ID in the commit-graph. This will only return a
  * commit if the ID exists both in the graph and in the object database such
  * that we don't return commits whose object has been pruned. Otherwise, this