diff --git a/main/src/main/scala/sbt/internal/Repository.scala b/main/src/main/scala/sbt/internal/Repository.scala
new file mode 100644
index 000000000..239dd02ef
--- /dev/null
+++ b/main/src/main/scala/sbt/internal/Repository.scala
@@ -0,0 +1,34 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal
+
+/**
+ * Represents an abstract cache of values, accessible by a key. The interface is deliberately
+ * minimal to give maximum flexibility to the implementation classes. For example, one can construct
+ * a cache from a `sbt.io.FileTreeRepository` that automatically registers the paths with the
+ * cache (but does not clear the cache on close):
+ * {{{
+ *  val repository = sbt.io.FileTreeRepository.default(_.getPath)
+ *  val fileCache = new Repository[Seq, (Path, Boolean), TypedPath] {
+ *    override def get(key: (Path, Boolean)): Seq[TypedPath] = {
+ *      val (path, recursive) = key
+ *      val depth = if (recursive) Int.MaxValue else 0
+ *      repository.register(path, depth)
+ *      repository.list(path, depth, AllPass)
+ *    }
+ *    override def close(): Unit = {}
+ *  }
+ * }}}
+ *
+ * @tparam M the container type of the cache. This will most commonly be `Option` or `Seq`.
+ * @tparam K the key type
+ * @tparam V the value type
+ */
+trait Repository[M[_], K, V] extends AutoCloseable {
+  def get(key: K): M[V]
+}