Support newer scalafmt versions which require a config file

build.sc

@@ -124,7 +124,7 @@ object Deps {
   val sbtTestInterface = ivy"org.scala-sbt:test-interface:1.0"
   val scalaCheck = ivy"org.scalacheck::scalacheck:1.15.4"
   def scalaCompiler(scalaVersion: String) = ivy"org.scala-lang:scala-compiler:${scalaVersion}"
-  val scalafmtDynamic = ivy"org.scalameta::scalafmt-dynamic:3.0.8"
+  val scalafmtDynamic = ivy"org.scalameta::scalafmt-dynamic:3.4.3"
   val scalametaTrees = ivy"org.scalameta::trees:4.5.0"
   def scalaReflect(scalaVersion: String) = ivy"org.scala-lang:scala-reflect:${scalaVersion}"
   def scalacScoveragePlugin = ivy"org.scoverage:::scalac-scoverage-plugin:1.4.11"
@@ -428,7 +428,8 @@ object scalalib extends MillModule {
       Seq(
         "-Djna.nosys=true",
         "-DMILL_BUILD_LIBRARIES=" + genIdeaArgs.map(_.path).mkString(","),
-        "-DMILL_SCALA_LIB=" + runClasspath().map(_.path).mkString(",")
+        "-DMILL_SCALA_LIB=" + runClasspath().map(_.path).mkString(","),
+        s"-DTEST_SCALAFMT_VERSION=${Deps.scalafmtDynamic.dep.version}"
       )
   }
   object backgroundwrapper extends MillPublishModule {

scalalib/src/scalafmt/ScalafmtModule.scala

@@ -1,6 +1,7 @@
 package mill.scalalib.scalafmt
 
 import mill._
+import mill.api.Result
 import mill.define._
 import mill.scalalib._
 
@@ -11,7 +12,7 @@ trait ScalafmtModule extends JavaModule {
       .worker()
       .reformat(
         filesToFormat(sources()),
-        scalafmtConfig().head
+        resolvedScalafmtConfig()
       )
   }
 
@@ -20,12 +21,28 @@ trait ScalafmtModule extends JavaModule {
       .worker()
       .checkFormat(
         filesToFormat(sources()),
-        scalafmtConfig().head
+        resolvedScalafmtConfig()
       )
   }
 
   def scalafmtConfig: Sources = T.sources(T.workspace / ".scalafmt.conf")
 
+  // TODO: Do we want provide some defaults or write a default file?
+  private[ScalafmtModule] def resolvedScalafmtConfig: Task[PathRef] = T.task {
+    val locs = scalafmtConfig()
+    locs.find(p => os.exists(p.path)) match {
+      case None => Result.Failure(s"None of the specified `scalafmtConfig` locations exist. Searched in: ${locs.map(_.path).mkString(", ")}")
+      case Some(c) if (os.read.lines.stream(c.path).find(_.trim.startsWith("version")).isEmpty) =>
+        Result.Failure(
+          s"""Found scalafmtConfig file does not specify to scalafmt version to use.
+            |Please specify the scalafmt version in ${c}
+            |Example:
+            |version = "2.4.3"
+            |""".stripMargin)
+      case Some(c) => Result.Success(c)
+    }
+  }
+
   protected def filesToFormat(sources: Seq[PathRef]) = {
     for {
       pathRef <- sources if os.exists(pathRef.path)
@@ -52,7 +69,7 @@ object ScalafmtModule extends ExternalModule with ScalafmtModule {
         .worker()
         .reformat(
           files,
-          scalafmtConfig().head
+          resolvedScalafmtConfig()
         )
     }
 
@@ -63,7 +80,7 @@ object ScalafmtModule extends ExternalModule with ScalafmtModule {
         .worker()
         .checkFormat(
           files,
-          scalafmtConfig().head
+          resolvedScalafmtConfig()
         )
     }
 

scalalib/src/scalafmt/ScalafmtWorker.scala

@@ -1,19 +1,12 @@
 package mill.scalalib.scalafmt
 
-import java.nio.file.{Paths => JPaths}
-
 import mill._
 import mill.define.{Discover, ExternalModule, Worker}
 import mill.api.Ctx
 import org.scalafmt.interfaces.Scalafmt
 
 import scala.collection.mutable
 import mill.api.Result
-import java.nio.file.Files
-import scala.util.Try
-import java.nio.file.Path
-import scala.util.Failure
-import scala.util.Success
 
 object ScalafmtWorkerModule extends ExternalModule {
   def worker: Worker[ScalafmtWorker] = T.worker { new ScalafmtWorker() }
@@ -66,24 +59,8 @@ private[scalafmt] class ScalafmtWorker {
 
       val scalafmt = Scalafmt
         .create(this.getClass.getClassLoader)
-        .withRespectVersion(false)
 
-      def readDefaultScalafmtConfig(): Try[Path] = {
-        Try(JPaths.get(getClass.getResource("default.scalafmt.conf").toURI))
-      }
-
-      val (configPath, tmpFileCreated) =
-        if (os.exists(scalafmtConfig.path))
-          (scalafmtConfig.path.toNIO, false)
-        else {
-          readDefaultScalafmtConfig() match {
-            case Success(defaultConfig) => (defaultConfig, false)
-            case Failure(exception) => {
-              ctx.log.debug(s"Read default scalafmt config fail, create a temp one")
-              (JPaths.get(Files.createTempFile("temp", ".scalafmt.conf").toUri), true)
-            }
-          }
-        }
+      val configPath = scalafmtConfig.path.toNIO
 
       // keeps track of files that are misformatted
       val misformatted = mutable.ListBuffer.empty[PathRef]
@@ -109,10 +86,6 @@ private[scalafmt] class ScalafmtWorker {
 
       }
 
-      if (tmpFileCreated) {
-        Files.delete(configPath)
-      }
-
       configSig = scalafmtConfig.sig
       misformatted.toList
     } else {

scalalib/test/src/scalafmt/ScalafmtTests.scala

@@ -10,6 +10,8 @@ import utest.framework.TestPath
 
 object ScalafmtTests extends TestSuite {
 
+  val scalafmtTestVersion = sys.props.getOrElse("TEST_SCALAFMT_VERSION", ???)
+
   trait TestBase extends TestUtil.BaseModule {
     def millSourcePath =
       TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
@@ -43,6 +45,12 @@ object ScalafmtTests extends TestSuite {
     os.remove.all(eval.outPath)
     os.makeDir.all(m.millSourcePath / os.up)
     os.copy(resourcePath, m.millSourcePath)
+    os.write(
+      m.millSourcePath / ".scalafmt.conf",
+      s"""version = $scalafmtTestVersion
+         |runner.dialect = scala213
+         |""".stripMargin
+    )
     t(eval)
   }