Support Mill 1

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

@@ -90,11 +90,18 @@ final class MillAlg[F[_]](defaultResolvers: List[Resolver])(implicit
   override protected val scalafixIssue: Option[String] =
     Some("https://github.com/scala-steward-org/scala-steward/issues/2838")
 
-  private def getMillVersion(buildRootDir: File): F[Option[Version]] =
-    List(
-      buildRootDir / s".$millVersionName",
-      buildRootDir / ".config" / millVersionName
-    ).collectFirstSomeM(fileAlg.readFile).map(_.flatMap(parser.parseMillVersion))
+  private def getMillVersion(buildRootDir: File): F[Option[Version]] = {
+    val fromConfigFile =
+      List(
+        buildRootDir / s".$millVersionName",
+        buildRootDir / ".config" / millVersionName
+      ).collectFirstSomeM(fileAlg.readFile).map(_.flatMap(parser.parseMillVersion))
+    val fromBuildFile = List(buildRootDir / "build.mill", buildRootDir / "build.mill.scala")
+      .collectFirstSomeM(fileAlg.readFile)
+      .map(_.flatMap(parser.parseBuildFileMillVersion))
+
+    fromBuildFile.orElse(fromConfigFile)
+  }
 
   private def getMillPluginDeps(
       millVersion: Version,

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

@@ -46,6 +46,13 @@ object parser {
   def parseMillVersion(s: String): Option[Version] =
     Option(s.trim).filter(_.nonEmpty).map(Version.apply)
 
+  private val millVersionRegex = """\s*\/\/\|\s*mill-version:\s*['"]?(.+?)['"]?\s*""".r
+  def parseBuildFileMillVersion(s: String): Option[Version] = {
+    s.linesIterator.collectFirst {
+      case millVersionRegex(version) => Version(version)
+    }
+  }
+
   /** Used to correctly format the Mill plugin artifacts will when included look like:
     *   - import $ivy.`com.goyeau::mill-scalafix::0.2.10`
     *

modules/core/src/test/scala/org/scalasteward/core/buildtool/mill/MillVersionParserTest.scala

@@ -19,4 +19,31 @@ class MillVersionParserTest extends FunSuite {
     val parsed = parser.parseMillVersion(versionFileContent).map(_.value)
     assertEquals(parsed, expected)
   }
+
+  test(s"parse version from build.mill file") {
+    val buildMillFileContent = """
+      |//|
+      |//| mill-version: 1.0.5
+      |""".stripMargin
+    val parsed = parser.parseBuildFileMillVersion(buildMillFileContent).map(_.value)
+    assertEquals(parsed, Some("1.0.5"))
+  }
+
+  test(s"parse quoted version from build.mill file") {
+    val buildMillFileContent = """
+      |//|
+      |//| mill-version: "1.0.5"
+      |""".stripMargin
+    val parsed = parser.parseBuildFileMillVersion(buildMillFileContent).map(_.value)
+    assertEquals(parsed, Some("1.0.5"))
+  }
+
+  test(s"parse single quoted version from build.mill file") {
+    val buildMillFileContent = """
+      |//|
+      |//| mill-version: '1.0.5'
+      |""".stripMargin
+    val parsed = parser.parseBuildFileMillVersion(buildMillFileContent).map(_.value)
+    assertEquals(parsed, Some("1.0.5"))
+  }
 }

project/Dependencies.scala

@@ -44,6 +44,6 @@ object Dependencies {
   val scalacheck = "org.scalacheck" %% "scalacheck" % "1.19.0"
   val scalaStewardMillPluginArtifactName = "scala-steward-mill-plugin"
   val scalaStewardMillPlugin =
-    "org.scala-steward" % s"${scalaStewardMillPluginArtifactName}_mill0.11_2.13" % "0.18.2"
+    "org.scala-steward" % s"${scalaStewardMillPluginArtifactName}_mill1_3" % "0.18.2-9-0ad5e5"
   val tomlj = "org.tomlj" % "tomlj" % "1.1.1"
 }