commit-graph: Create `git_commit_graph` as an abstraction for the file

This change does a medium-size refactor of the git_commit_graph_file and
the interaction with the ODB. Now instead of the ODB owning a direct
reference to the git_commit_graph_file, there will be an intermediate
git_commit_graph. The main advantage of that is that now end users can
explicitly set a git_commit_graph that is eagerly checked for errors,
while still being able to lazily use the commit-graph in a regular ODB,
if the file is present.

3 files changed, 63 insertions, 0 deletions

diff --git a/include/git2/odb.h b/include/git2/odb.h
index c4bfa5290..dd481e950 100644
--- a/include/git2/odb.h
+++ b/include/git2/odb.h
@@ -544,6 +544,21 @@ GIT_EXTERN(size_t) git_odb_num_backends(git_odb *odb);
  */
 GIT_EXTERN(int) git_odb_get_backend(git_odb_backend **out, git_odb *odb, size_t pos);
 
+/**
+ * Set the git commit-graph for the ODB.
+ *
+ * After a successfull call, the ownership of the cgraph parameter will be
+ * transferred to libgit2, and the caller should not free it.
+ *
+ * The commit-graph can also be unset by explicitly passing NULL as the cgraph
+ * parameter.
+ *
+ * @param odb object database
+ * @param cgraph the git commit-graph
+ * @return 0 on success; error code otherwise
+ */
+GIT_EXTERN(int) git_odb_set_commit_graph(git_odb *odb, git_commit_graph *cgraph);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/include/git2/sys/commit_graph.h b/include/git2/sys/commit_graph.h
new file mode 100644
index 000000000..038c9b739
--- /dev/null
+++ b/include/git2/sys/commit_graph.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_sys_git_commit_graph_h__
+#define INCLUDE_sys_git_commit_graph_h__
+
+#include "git2/common.h"
+#include "git2/types.h"
+
+/**
+ * @file git2/sys/commit_graph.h
+ * @brief Git commit-graph
+ * @defgroup git_commit_graph Git commit-graph APIs
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/**
+ * Opens a `git_commit_graph` from a path to an objects directory.
+ *
+ * This finds, opens, and validates the `commit-graph` file.
+ *
+ * @param cgraph_out the `git_commit_graph` struct to initialize.
+ * @param objects_dir the path to a git objects directory.
+ * @return Zero on success; -1 on failure.
+ */
+GIT_EXTERN(int) git_commit_graph_open(git_commit_graph **cgraph_out, const char *objects_dir);
+
+/**
+ * Frees commit-graph data. This should only be called when memory allocated
+ * using `git_commit_graph_open` is not returned to libgit2 because it was not
+ * associated with the ODB through a successful call to
+ * `git_odb_set_commit_graph`.
+ *
+ * @param cgraph the commit-graph object to free. If NULL, no action is taken.
+ */
+GIT_EXTERN(void) git_commit_graph_free(git_commit_graph *cgraph);
+
+GIT_END_DECL
+
+#endif
diff --git a/include/git2/types.h b/include/git2/types.h
index ade0c7d32..562eb8e5f 100644
--- a/include/git2/types.h
+++ b/include/git2/types.h
@@ -102,6 +102,9 @@ typedef struct git_refdb git_refdb;
 /** A custom backend for refs */
 typedef struct git_refdb_backend git_refdb_backend;
 
+/** A git commit-graph */
+typedef struct git_commit_graph git_commit_graph;
+
 /**
  * Representation of an existing git repository,
  * including all its object contents