Revised .mill-version update support

Author: lefou

modules/core/src/main/scala/org/scalasteward/core/buildtool/mill/MillAlg.scala

@@ -90,7 +90,9 @@ object MillAlg {
   private def millMainArtifact(version: String): Dependency =
     Dependency(millMainGroupId, millMainArtifactId, version)
 
-  def isMillMainUpdate(update: Update.Single): Boolean =
-    update.groupId === millMainGroupId && update.artifactId.name === millMainArtifactId.name
+  def isMillMainUpdate(update: Update): Boolean =
+    update.groupId === millMainGroupId && update.artifactIds.exists(
+      _.name === millMainArtifactId.name
+    )
 
 }

modules/core/src/main/scala/org/scalasteward/core/edit/UpdateHeuristic.scala

@@ -214,6 +214,7 @@ object UpdateHeuristic {
       case update: Update.Single if isScalafmtUpdate(update) =>
         defaultReplaceVersion(_ => List("version"))(update)
       case update: Update.Single if MillAlg.isMillMainUpdate(update) =>
+        // this is intended to update the `.mill-version`
         content => if (content === update.currentVersion) Some(update.nextVersion) else None
       case _ =>
         _ => None

modules/core/src/main/scala/org/scalasteward/core/io/package.scala

@@ -18,6 +18,7 @@ package org.scalasteward.core
 
 import better.files.File
 import cats.syntax.all._
+import org.scalasteward.core.buildtool.mill.MillAlg
 import org.scalasteward.core.data.{GroupId, Update}
 import org.scalasteward.core.scalafmt.{scalafmtArtifactId, scalafmtConfName, scalafmtGroupId}
 
@@ -31,9 +32,10 @@ package object io {
       file: File
   ): Boolean =
     () match {
-      case _ if isSbtUpdate(update)          => file.name === "build.properties"
-      case _ if isScalafmtCoreUpdate(update) => file.name === scalafmtConfName
-      case _                                 => isGenericSourceFile(file, fileExtensions)
+      case _ if isSbtUpdate(update)              => file.name === "build.properties"
+      case _ if isScalafmtCoreUpdate(update)     => file.name === scalafmtConfName
+      case _ if MillAlg.isMillMainUpdate(update) => file.name === ".mill-version"
+      case _                                     => isGenericSourceFile(file, fileExtensions)
     }
 
   private def isGenericSourceFile(file: File, fileExtensions: Set[String]): Boolean =

modules/core/src/main/scala/org/scalasteward/core/repoconfig/UpdatesConfig.scala

@@ -74,7 +74,7 @@ final case class UpdatesConfig(
 
 object UpdatesConfig {
   val defaultFileExtensions: Set[String] =
-    Set(".mill-version", ".scala", ".sbt", ".sbt.shared", ".sc", ".yml", "pom.xml")
+    Set(".scala", ".sbt", ".sbt.shared", ".sc", ".yml", "pom.xml")
 
   implicit val updatesConfigEq: Eq[UpdatesConfig] =
     Eq.fromUniversalEquals