1 files changed, 57 insertions, 0 deletions
diff --git a/scalalib/src/scalafmt/ScalafmtWorker.scala b/scalalib/src/scalafmt/ScalafmtWorker.scala
new file mode 100644
index 00000000..47d8375f
--- /dev/null
+++ b/scalalib/src/scalafmt/ScalafmtWorker.scala
@@ -0,0 +1,57 @@
+package mill.scalalib.scalafmt
+
+import mill._
+import mill.define.{Discover, ExternalModule, Worker}
+import mill.modules.Jvm
+import mill.api.Ctx
+
+import scala.collection.mutable
+
+object ScalafmtWorkerModule extends ExternalModule {
+  def worker: Worker[ScalafmtWorker] = T.worker { new ScalafmtWorker() }
+
+  lazy val millDiscover = Discover[this.type]
+}
+
+private[scalafmt] class ScalafmtWorker {
+  private val reformatted: mutable.Map[os.Path, Int] = mutable.Map.empty
+  private var configSig: Int = 0
+
+  def reformat(input: Seq[PathRef],
+               scalafmtConfig: PathRef,
+               scalafmtClasspath: Agg[os.Path])(implicit ctx: Ctx): Unit = {
+    val toFormat =
+      if (scalafmtConfig.sig != configSig) input
+      else
+        input.filterNot(ref => reformatted.get(ref.path).contains(ref.sig))
+
+    if (toFormat.nonEmpty) {
+      ctx.log.info(s"Formatting ${toFormat.size} Scala sources")
+      reformatAction(toFormat.map(_.path),
+                     scalafmtConfig.path,
+                     scalafmtClasspath)
+      reformatted ++= toFormat.map { ref =>
+        val updRef = PathRef(ref.path)
+        updRef.path -> updRef.sig
+      }
+      configSig = scalafmtConfig.sig
+    } else {
+      ctx.log.info(s"Everything is formatted already")
+    }
+  }
+
+  private val cliFlags = Seq("--non-interactive", "--quiet")
+
+  private def reformatAction(toFormat: Seq[os.Path],
+                             config: os.Path,
+                             classpath: Agg[os.Path])(implicit ctx: Ctx) = {
+    val configFlags =
+      if (os.exists(config)) Seq("--config", config.toString) else Seq.empty
+    Jvm.runSubprocess(
+      "org.scalafmt.cli.Cli",
+      classpath,
+      mainArgs = toFormat.map(_.toString) ++ configFlags ++ cliFlags
+    )
+  }
+
+}