Support several scalafixScalaBinaryVersion within a build

src/main/scala/scalafix/internal/sbt/ScalafixInterface.scala

@@ -116,47 +116,60 @@ object ScalafixInterface {
     private lazy val _value = scala.util.Try(thunk())
     override def apply(): T = _value.get
   }
+  private val fromToolClasspathMemo: BlockingCache[
+    (String, Seq[ModuleID], Seq[Repository]),
+    ScalafixInterface
+  ] = new BlockingCache
+
   def fromToolClasspath(
       scalafixBinaryScalaVersion: String,
       scalafixDependencies: Seq[ModuleID],
       scalafixCustomResolvers: Seq[Repository],
       logger: Logger = ConsoleLogger(System.out)
   ): () => ScalafixInterface =
     new LazyValue({ () =>
-      if (scalafixBinaryScalaVersion.startsWith("3"))
-        logger.error(
-          "To use Scalafix on Scala 3 projects, you must unset `scalafixBinaryScalaVersion`. " +
-            "Rules such as ExplicitResultTypes requiring the project version to match the Scalafix " +
-            "version are unsupported for the moment."
-        )
-      else if (scalafixBinaryScalaVersion == "2.11")
-        logger.error(
-          "Scala 2.11 is no longer supported. Please downgrade to the final version supporting " +
-            "it: sbt-scalafix 0.10.4."
-        )
-      val callback = new ScalafixLogger(logger)
-      val scalafixArguments = ScalafixAPI
-        .fetchAndClassloadInstance(
+      fromToolClasspathMemo.getOrElseUpdate(
+        (
           scalafixBinaryScalaVersion,
-          scalafixCustomResolvers.asJava
-        )
-        .newArguments()
-        .withMainCallback(callback)
-      val printStream =
-        new PrintStream(
-          LoggingOutputStream(
-            logger,
-            Level.Info
-          )
-        )
-      new ScalafixInterface(scalafixArguments, Nil)
-        .withArgs(
-          Arg.PrintStream(printStream),
-          Arg.ToolClasspath(
-            Nil,
-            scalafixDependencies,
-            scalafixCustomResolvers
-          )
-        )
+          scalafixDependencies,
+          scalafixCustomResolvers
+        ), {
+          if (scalafixBinaryScalaVersion.startsWith("3"))
+            logger.error(
+              "To use Scalafix on Scala 3 projects, you must unset `scalafixBinaryScalaVersion`. " +
+                "Rules such as ExplicitResultTypes requiring the project version to match the Scalafix " +
+                "version are unsupported for the moment."
+            )
+          else if (scalafixBinaryScalaVersion == "2.11")
+            logger.error(
+              "Scala 2.11 is no longer supported. Please downgrade to the final version supporting " +
+                "it: sbt-scalafix 0.10.4."
+            )
+          val callback = new ScalafixLogger(logger)
+          val scalafixArguments = ScalafixAPI
+            .fetchAndClassloadInstance(
+              scalafixBinaryScalaVersion,
+              scalafixCustomResolvers.asJava
+            )
+            .newArguments()
+            .withMainCallback(callback)
+          val printStream =
+            new PrintStream(
+              LoggingOutputStream(
+                logger,
+                Level.Info
+              )
+            )
+          new ScalafixInterface(scalafixArguments, Nil)
+            .withArgs(
+              Arg.PrintStream(printStream),
+              Arg.ToolClasspath(
+                Nil,
+                scalafixDependencies,
+                scalafixCustomResolvers
+              )
+            )
+        }
+      )
     })
 }

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

@@ -158,6 +158,11 @@ object ScalafixPlugin extends AutoPlugin {
         SettingKey[Boolean]("bspEnabled") := false
       )
     ),
+    scalafixInterfaceProvider := ScalafixInterface.fromToolClasspath(
+      scalafixScalaBinaryVersion.value,
+      scalafixDependencies = scalafixDependencies.value,
+      scalafixCustomResolvers = scalafixResolvers.value
+    ),
     update := {
       object SemanticdbScalac {
         def unapply(id: ModuleID): Option[String] =
@@ -211,11 +216,6 @@ object ScalafixPlugin extends AutoPlugin {
         ),
     scalafixDependencies := Nil,
     commands += ScalafixEnable.command,
-    scalafixInterfaceProvider := ScalafixInterface.fromToolClasspath(
-      (ThisBuild / scalafixScalaBinaryVersion).value,
-      scalafixDependencies = (ThisBuild / scalafixDependencies).value,
-      scalafixCustomResolvers = (ThisBuild / scalafixResolvers).value
-    ),
     scalafixInterfaceCache := new BlockingCache[
       ToolClasspath,
       ScalafixInterface

src/sbt-test/sbt-scalafix/cross-build-advanced/.scalafix-2.conf

@@ -0,0 +1,3 @@
+rules = [DisableSyntax, OrganizeImports, ExplicitResultTypes]
+OrganizeImports.removeUnused = true
+ExplicitResultTypes.skipSimpleDefinitions = false

src/sbt-test/sbt-scalafix/cross-build-advanced/.scalafix-3.conf

@@ -0,0 +1,2 @@
+rules = [DisableSyntax, OrganizeImports]
+OrganizeImports.removeUnused = false

src/sbt-test/sbt-scalafix/cross-build-advanced/build.sbt

@@ -0,0 +1,23 @@
+import _root_.scalafix.sbt.{BuildInfo => Versions}
+
+val scala3Version = "3.3.0"
+ThisBuild / semanticdbEnabled := true
+ThisBuild / semanticdbVersion := scalafixSemanticdb.revision
+
+lazy val root = project
+  .in(file("."))
+  .settings(
+    scalaVersion := Versions.scala212,
+    crossScalaVersions := Seq(Versions.scala212, Versions.scala213, scala3Version),
+    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"))
+      else
+         Some(file(".scalafix-2.conf"))
+    }
+  )

src/sbt-test/sbt-scalafix/cross-build-advanced/project/plugins.sbt

@@ -0,0 +1,2 @@
+resolvers += Resolver.sonatypeRepo("public")
+addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % sys.props("plugin.version"))

src/sbt-test/sbt-scalafix/cross-build-advanced/src/main/scala-2/Main.scala

@@ -0,0 +1,7 @@
+import scala.Int
+import scala.collection.Seq
+import scala.collection.AbstractSeq
+
+object Main {
+  def foo(a: Int) = a + 2.0f
+}

src/sbt-test/sbt-scalafix/cross-build-advanced/src/main/scala-2/Main.scala.expected

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

src/sbt-test/sbt-scalafix/cross-build-advanced/src/main/scala-3/Main.scala

@@ -0,0 +1,7 @@
+import scala.Int
+import scala.collection.Seq
+import scala.collection.AbstractSeq
+
+object Main {
+  def foo(a: Int) = a + 2.0f
+}

src/sbt-test/sbt-scalafix/cross-build-advanced/src/main/scala-3/Main.scala.expected

@@ -0,0 +1,7 @@
+import scala.Int
+import scala.collection.AbstractSeq
+import scala.collection.Seq
+
+object Main {
+  def foo(a: Int) = a + 2.0f
+}

src/sbt-test/sbt-scalafix/cross-build-advanced/test

@@ -0,0 +1,6 @@
+> +compile
+
+> +scalafix
+
+$ must-mirror src/main/scala-2/Main.scala src/main/scala-2/Main.scala.expected
+$ must-mirror src/main/scala-3/Main.scala src/main/scala-3/Main.scala.expected