let scalafixScalaBV follow scalaBV to leverage 2.13 and deprecate it

src/main/scala/scalafix/sbt/ScalafixPlugin.scala

@@ -9,13 +9,13 @@ import sbt.*
 import sbt.internal.sbtscalafix.JLineAccess
 import sbt.internal.util.complete.Parser
 import sbt.plugins.JvmPlugin
+import sbt.librarymanagement.ResolveException
 import scalafix.interfaces.{ScalafixError, ScalafixMainCallback}
 import scalafix.internal.sbt.*
 
+import scala.annotation.nowarn
 import scala.collection.JavaConverters.collectionAsScalaIterableConverter
 import scala.util.control.NoStackTrace
-import sbt.librarymanagement.ResolveException
-
 import scala.util.Try
 
 object ScalafixPlugin extends AutoPlugin {
@@ -64,10 +64,15 @@ object ScalafixPlugin extends AutoPlugin {
         "Optional list of artifacts to resolve to run custom rules. " +
           "Can be set in ThisBuild or at project-level."
       )
+    @deprecated(
+      "scalafixScalaBinaryVersion now follows scalaBinaryVersion by default",
+      "0.12.1"
+    )
     val scalafixScalaBinaryVersion: SettingKey[String] =
       settingKey[String](
         "The Scala binary version used for scalafix execution. Can be set in ThisBuild or at project-level. " +
-          "Custom rules must be compiled against that binary version. Defaults to 2.12."
+          "Custom rules must be compiled against that binary version. Defaults to 2.12 for 2.12 projects, " +
+          "2.13 otherwise."
       )
     val scalafixConfig: SettingKey[Option[File]] =
       settingKey[Option[File]](
@@ -155,7 +160,7 @@ object ScalafixPlugin extends AutoPlugin {
         loadedRules = { () =>
           val scalafixInterface = ScalafixInterface(
             scalafixInterfaceCache.value,
-            scalafixScalaBinaryVersion.value,
+            scalafixScalaBinaryVersion.value: @nowarn,
             toolClasspath = Arg.ToolClasspath(
               // Local rules classpath must be looked up via tasks so they can't appear in completions
               Nil,
@@ -266,6 +271,13 @@ object ScalafixPlugin extends AutoPlugin {
   )
 
   override lazy val globalSettings: Seq[Def.Setting[_]] = Seq(
+    // use derive to support per-level values while allowing user to override at ThisBuild level
+    Def.derive((scalafixScalaBinaryVersion: @nowarn) := {
+      scalaBinaryVersion.value match {
+        case "2.12" => "2.12"
+        case _ => "2.13"
+      }
+    }),
     scalafixCallback := new ScalafixLogger(ScalafixInterface.defaultLogger),
     scalafixConfig := None, // let scalafix-cli try to infer $CWD/.scalafix.conf
     scalafixOnCompile := false,
@@ -300,7 +312,6 @@ object ScalafixPlugin extends AutoPlugin {
           )
         }
       },
-      scalafixScalaBinaryVersion := "2.12",
       scalafixJGitCompletion := new JGitCompletion(baseDirectory.value.toPath)
     )
 
@@ -433,7 +444,7 @@ object ScalafixPlugin extends AutoPlugin {
         shellArgs,
         projectDepsExternal,
         projectDepsInternal,
-        scalafixScalaBinaryVersion.value,
+        scalafixScalaBinaryVersion.value: @nowarn,
         scalafixDependencies.value,
         allResolvers,
         (ThisBuild / scalafixCallback).value,

src/sbt-test/sbt-1.4/build-lint/build.sbt

@@ -1,6 +1,5 @@
 ThisBuild / scalafixDependencies := Nil
 ThisBuild / scalafixResolvers := Nil
-ThisBuild / scalafixScalaBinaryVersion := "2.12"
 scalafixCaching := false
 scalafixConfig := None
 scalafixOnCompile := false

src/sbt-test/sbt-1.5/cross-build-scala3/.scalafix-2.conf

@@ -0,0 +1,2 @@
+rules = [OrganizeImports, ExplicitResultTypes]
+ExplicitResultTypes.skipSimpleDefinitions = false

src/sbt-test/sbt-1.5/cross-build-scala3/.scalafix-3.conf

@@ -0,0 +1 @@
+rules = [OrganizeImports]

src/sbt-test/sbt-1.5/cross-build-scalafixScalaBinaryVersion/build.sbt → src/sbt-test/sbt-1.5/cross-build-scala3/build.sbt

@@ -1,6 +1,6 @@
 import _root_.scalafix.sbt.{BuildInfo => Versions}
 
-val scala3Version = "3.3.0"
+val scala3Version = "3.4.1"
 ThisBuild / semanticdbEnabled := true
 ThisBuild / semanticdbVersion := scalafixSemanticdb.revision
 
@@ -16,10 +16,6 @@ lazy val root = project
     scalacOptions ++= (if (scalaVersion.value.startsWith("2"))
                          Seq("-Ywarn-unused")
                        else Seq()),
-    scalafixScalaBinaryVersion := {
-      if (scalaBinaryVersion.value == "3") scalafixScalaBinaryVersion.value
-      else scalaBinaryVersion.value
-    },
     scalafixConfig := {
       if (scalaBinaryVersion.value == "3")
         Some(file(".scalafix-3.conf"))

src/sbt-test/sbt-1.5/cross-build-scala3/src/main/scala-3/Main.scala.expected

@@ -0,0 +1,5 @@
+import scala.Int
+
+object Main {
+  def foo(a: Int) = a + 2.0f
+}

src/sbt-test/sbt-scalafix/local-rules/build.sbt

@@ -7,10 +7,7 @@ inThisBuild(
       "ch.epfl.scala" %% "example-scalafix-rule" % "1.4.0"
     ),
     resolvers += Resolver.sonatypeRepo("snapshots"),
-    scalaVersion := "2.13.11", // out of sync with scalafix.sbt.BuildInfo.scala213 on purpose
-    scalafixScalaBinaryVersion :=
-      // this should be the default in sbt-scalafix 1.0
-      CrossVersion.binaryScalaVersion(scalaVersion.value)
+    scalaVersion := "2.13.11" // out of sync with scalafix.sbt.BuildInfo.scala213 on purpose
   )
 )