Cache Scalafix instances globally

mill-scalafix/src/com/goyeau/mill/scalafix/ScalafixCache.scala

@@ -0,0 +1,24 @@
+package com.goyeau.mill.scalafix
+
+import com.goyeau.mill.scalafix.CoursierUtils
+import coursier.core.Repository
+import scalafix.interfaces.Scalafix
+
+import scala.collection.mutable
+import scala.ref.SoftReference
+import scala.jdk.CollectionConverters._
+
+private[scalafix] object ScalafixCache {
+
+  private val cache = mutable.Map.empty[(String, Seq[Repository]), SoftReference[Scalafix]]
+
+  def getOrElseCreate(scalaVersion: String, repositories: Seq[Repository]) =
+    cache.get((scalaVersion, repositories)) match {
+      case Some(SoftReference(value)) => value
+      case _ =>
+        val newResult =
+          Scalafix.fetchAndClassloadInstance(scalaVersion, repositories.map(CoursierUtils.toApiRepository).asJava)
+        cache.update((scalaVersion, repositories), SoftReference(newResult))
+        newResult
+    }
+}

mill-scalafix/src/com/goyeau/mill/scalafix/ScalafixModule.scala

@@ -77,8 +77,8 @@ object ScalafixModule {
       wd: os.Path
   ): Result[Unit] =
     if (sources.nonEmpty) {
-      val scalafix = Scalafix
-        .fetchAndClassloadInstance(scalaVersion, repositories.map(CoursierUtils.toApiRepository).asJava)
+      val scalafix = ScalafixCache
+        .getOrElseCreate(scalaVersion, repositories)
         .newArguments()
         .withParsedArguments(args.asJava)
         .withWorkingDirectory(wd.toNIO)