midx: add options to writer function

Provide an options structure to MIDX writing. This allows us to
specify information (like OID type) during writer creation.

include/git2/sys/midx.h

@@ -19,6 +19,44 @@
  */
 GIT_BEGIN_DECL
 
+/**
+ * Options structure for `git_midx_writer_options`.
+ *
+ * Initialize with `GIT_MIDX_WRITER_OPTIONS_INIT`. Alternatively,
+ * you can use `git_midx_writer_options_init`.
+ */
+typedef struct {
+	unsigned int version;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	/** The object ID type that this commit graph contains. */
+	git_oid_t oid_type;
+#endif
+} git_midx_writer_options;
+
+/** Current version for the `git_midx_writer_options` structure */
+#define GIT_MIDX_WRITER_OPTIONS_VERSION 1
+
+/** Static constructor for `git_midx_writer_options` */
+#define GIT_MIDX_WRITER_OPTIONS_INIT { \
+		GIT_MIDX_WRITER_OPTIONS_VERSION \
+	}
+
+/**
+ * Initialize git_midx_writer_options structure
+ *
+ * Initializes a `git_midx_writer_options` with default values.
+ * Equivalent to creating an instance with
+ * `GIT_MIDX_WRITER_OPTIONS_INIT`.
+ *
+ * @param opts The `git_midx_writer_options` struct to initialize.
+ * @param version The struct version; pass `GIT_MIDX_WRITER_OPTIONS_VERSION`.
+ * @return Zero on success; -1 on failure.
+ */
+GIT_EXTERN(int) git_midx_writer_options_init(
+	git_midx_writer_options *opts,
+	unsigned int version);
+
 /**
  * Create a new writer for `multi-pack-index` files.
  *
@@ -31,7 +69,7 @@ GIT_EXTERN(int) git_midx_writer_new(
 		git_midx_writer **out,
 		const char *pack_dir
 #ifdef GIT_EXPERIMENTAL_SHA256
-		, git_oid_t oid_type
+		, git_midx_writer_options *options
 #endif
 		);
 

src/libgit2/midx.c

@@ -508,21 +508,29 @@ static int packfile__cmp(const void *a_, const void *b_)
 }
 
 int git_midx_writer_new(
-		git_midx_writer **out,
-		const char *pack_dir
+	git_midx_writer **out,
+	const char *pack_dir
 #ifdef GIT_EXPERIMENTAL_SHA256
-		, git_oid_t oid_type
+	, git_midx_writer_options *opts
 #endif
 		)
 {
 	git_midx_writer *w;
+	git_oid_t oid_type;
 
-#ifndef GIT_EXPERIMENTAL_SHA256
-	git_oid_t oid_type = GIT_OID_SHA1;
+	GIT_ASSERT_ARG(out && pack_dir);
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	GIT_ERROR_CHECK_VERSION(opts,
+		GIT_MIDX_WRITER_OPTIONS_VERSION,
+		"git_midx_writer_options");
+
+	oid_type = opts && opts->oid_type ? opts->oid_type : GIT_OID_DEFAULT;
+	GIT_ASSERT_ARG(git_oid_type_is_valid(oid_type));
+#else
+	oid_type = GIT_OID_SHA1;
 #endif
 
-	GIT_ASSERT_ARG(out && pack_dir && oid_type);
-
 	w = git__calloc(1, sizeof(git_midx_writer));
 	GIT_ERROR_CHECK_ALLOC(w);
 

src/libgit2/odb_pack.c

@@ -796,13 +796,21 @@ static int pack_backend__writemidx(git_odb_backend *_backend)
 	size_t i;
 	int error = 0;
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	git_midx_writer_options midx_opts = GIT_MIDX_WRITER_OPTIONS_INIT;
+#endif
+
 	GIT_ASSERT_ARG(_backend);
 
 	backend = (struct pack_backend *)_backend;
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	midx_opts.oid_type = backend->opts.oid_type;
+#endif
+
 	error = git_midx_writer_new(&w, backend->pack_folder
 #ifdef GIT_EXPERIMENTAL_SHA256
-		, backend->opts.oid_type
+		, &midx_opts
 #endif
 		);
 

tests/libgit2/pack/midx.c

@@ -59,7 +59,7 @@ void test_pack_midx__writer(void)
 	cl_git_pass(git_str_joinpath(&path, git_repository_path(repo), "objects/pack"));
 
 #ifdef GIT_EXPERIMENTAL_SHA256
-	cl_git_pass(git_midx_writer_new(&w, git_str_cstr(&path), GIT_OID_SHA1));
+	cl_git_pass(git_midx_writer_new(&w, git_str_cstr(&path), NULL));
 #else
 	cl_git_pass(git_midx_writer_new(&w, git_str_cstr(&path)));
 #endif