repo: add git_repository_wrap_odb() to wrap an ODB

Primarily useful when used together with git_odb_backend_one_pack().

include/git2/repository.h

@@ -36,6 +36,19 @@ GIT_BEGIN_DECL
 GIT_EXTERN(int) git_repository_open(git_repository **repository, const char *path);
 
 /**
+ * Create a "fake" repository to wrap an object database
+ *
+ * Create a repository object to wrap an object database to be used
+ * with the API when all you have is an object database. This doesn't
+ * have any paths associated with it, so use with care.
+ *
+ * @param repository pointer to the repo
+ * @param odb the object database to wrap
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_repository_wrap_odb(git_repository **repository, git_odb *odb);
+
+/**
  * Look for a git repository and copy its path in the given buffer.
  * The lookup start from base_path and walk across parent directories
  * if nothing has been found. The lookup ends when the first repository

src/repository.c

@@ -388,6 +388,19 @@ int git_repository_open(git_repository **repo_out, const char *path)
 		repo_out, path, GIT_REPOSITORY_OPEN_NO_SEARCH, NULL);
 }
 
+int git_repository_wrap_odb(git_repository **repo_out, git_odb *odb)
+{
+	git_repository *repo;
+
+	repo = repository_alloc();
+	GITERR_CHECK_ALLOC(repo);
+
+	git_repository_set_odb(repo, odb);
+	*repo_out = repo;
+
+	return 0;
+}
+
 int git_repository_discover(
 	char *repository_path,
 	size_t size,