Add treebuilder interface and Gentoo prototype

pkg/tree/builder.go

@@ -0,0 +1,28 @@
+// Copyright © 2019 Ettore Di Giacinto <mudler@gentoo.org>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, see <http://www.gnu.org/licenses/>.
+
+package tree
+
+import (
+	pkg "github.com/mudler/luet/pkg/package"
+)
+
+// reads a luet tree and generates the package lists
+type Builder interface {
+	Scan(string) error // compiles a tree
+	Load(string) error // pre-scanned tree
+
+	Generate() (pkg.PackageSet, error) // generates world
+}