1 files changed, 52 insertions, 0 deletions
diff --git a/tools/shared/src/main/scala/scala/scalajs/tools/io/CacheUtils.scala b/tools/shared/src/main/scala/scala/scalajs/tools/io/CacheUtils.scala
new file mode 100644
index 0000000..14773f8
--- /dev/null
+++ b/tools/shared/src/main/scala/scala/scalajs/tools/io/CacheUtils.scala
@@ -0,0 +1,52 @@
+package scala.scalajs.tools.io
+
+object CacheUtils {
+
+  def joinVersions(vs: Option[String]*): Option[String] = {
+    val bld = new StringBuilder
+
+    @scala.annotation.tailrec
+    def loop(vs: Seq[Option[String]]): Option[String] = {
+      vs match {
+        case Some(v) :: vss =>
+          bld.append(mangleVersionString(v))
+          loop(vss)
+        case None :: _ =>
+          None
+        case Nil =>
+          Some(bld.toString)
+      }
+    }
+
+    loop(vs.toList)
+  }
+
+  def joinVersions(vs: String*): String =
+    vs.map(mangleVersionString _).mkString
+
+  private def mangleVersionString(str: String) = s"${str.length}:$str"
+
+  def cached(version: Option[String], output: VirtualFile,
+      cache: Option[WritableVirtualTextFile])(action: => Unit): Unit = {
+
+    val upToDate = output.exists && (
+        for {
+          v <- version
+          c <- cache if c.exists
+        } yield c.content == v
+    ).getOrElse(false)
+
+    // Are we outdated?
+    if (!upToDate) {
+      action
+
+      // Write cache
+      for (c <- cache; v <- version) {
+        val w = c.contentWriter
+        try w.write(v)
+        finally w.close()
+      }
+    }
+  }
+
+}