Add wip code for config backends.

ext/rugged/rugged.h

@@ -40,6 +40,7 @@
 #include <assert.h>
 #include <git2.h>
 #include <git2/odb_backend.h>
+#include <git2/sys/config.h>
 #include <git2/sys/refdb_backend.h>
 #include <git2/sys/refs.h>
 #include <git2/sys/repository.h>

ext/rugged/rugged_config.c

@@ -384,6 +384,65 @@ static VALUE rb_git_config_transaction(VALUE self)
 	return rb_result;
 }
 
+/*
+ *  call-seq:
+ *    config.add_backend(backend, level, force = false) -> config
+ *
+ *  Add a backend to be used by the config.
+ *
+ *  A backend can only be assigned once, and becomes unusable from that
+ *  point on. Trying to assign a backend a second time will raise an
+ *  exception.
+ */
+static VALUE rb_git_config_add_backend(int argc, VALUE *argv, VALUE self)
+{
+	git_config *config;
+	git_config_backend *backend;
+	ID id_level;
+	git_config_level_t level;
+	VALUE rb_backend, rb_level, rb_force;
+
+	rb_scan_args(argc, argv, "21", &rb_backend, &rb_level, &rb_force);
+
+	// TODO: Check rb_backend
+
+	Check_Type(rb_level, T_SYMBOL);
+
+	id_level = SYM2ID(rb_level);
+
+	if (id_level == rb_intern("system")) {
+		level = GIT_CONFIG_LEVEL_SYSTEM;
+	} else if (id_level == rb_intern("xdg")) {
+		level = GIT_CONFIG_LEVEL_XDG;
+	} else if (id_level == rb_intern("global")) {
+		level = GIT_CONFIG_LEVEL_GLOBAL;
+	} else if (id_level == rb_intern("local")) {
+		level = GIT_CONFIG_LEVEL_LOCAL;
+	} else if (id_level == rb_intern("app")) {
+		level = GIT_CONFIG_LEVEL_APP;
+	} else if (id_level == rb_intern("highest")) {
+		level = GIT_CONFIG_HIGHEST_LEVEL;
+	} else {
+		rb_raise(rb_eArgError, "Invalid config backend level.");
+	}
+
+	// TODO: if (!NIL_P(rb_force) && rb_force != Qtrue && rb_force != Qfalse)
+
+	Data_Get_Struct(self, git_config, config);
+	Data_Get_Struct(rb_backend, git_config_backend, backend);
+
+	if (!backend)
+		rb_exc_raise(rb_exc_new2(rb_eRuntimeError, "Can not reuse config backend instances"));
+
+	rugged_exception_check(git_config_add_backend(config, backend, level, RTEST(rb_force)));
+
+	// libgit2 has taken ownership of the backend, so we should make sure
+	// we don't try to free it.
+	((struct RData *)rb_backend)->data = NULL;
+
+	return self;
+}
+
 void Init_rugged_config(void)
 {
 	/*
@@ -397,6 +456,8 @@ void Init_rugged_config(void)
 
 	rb_define_method(rb_cRuggedConfig, "delete", rb_git_config_delete, 1);
 
+	rb_define_method(rb_cRuggedConfig, "add_backend", rb_git_config_add_backend, -1);
+
 	rb_define_method(rb_cRuggedConfig, "store", rb_git_config_store, 2);
 	rb_define_method(rb_cRuggedConfig, "[]=", rb_git_config_store, 2);