Get rid of Fn1

build.sbt

@@ -143,6 +143,11 @@ val collectionProj = (project in file("internal") / "util-collection")
     mimaBinaryIssueFilters ++= Seq(
       // Added private[sbt] method to capture State attributes.
       exclude[ReversedMissingMethodProblem]("sbt.internal.util.AttributeMap.setCond"),
+
+      // Dropped in favour of plain scala.Function, and its compose method
+      exclude[MissingClassProblem]("sbt.internal.util.Fn1"),
+      exclude[DirectMissingMethodProblem]("sbt.internal.util.TypeFunctions.toFn1"),
+      exclude[DirectMissingMethodProblem]("sbt.internal.util.Types.toFn1"),
     ),
   )
   .configure(addSbtUtilPosition)
@@ -418,7 +423,14 @@ lazy val sbtProj = (project in file("sbt"))
     crossScalaVersions := Seq(baseScalaVersion),
     crossPaths := false,
     mimaSettings,
-    mimaBinaryIssueFilters ++= sbtIgnoredProblems,
+    mimaBinaryIssueFilters ++= Vector(
+      // Added more items to Import trait.
+      exclude[ReversedMissingMethodProblem]("sbt.Import.sbt$Import$_setter_$WatchSource_="),
+      exclude[ReversedMissingMethodProblem]("sbt.Import.WatchSource"),
+
+      // Dropped in favour of plain scala.Function, and its compose method
+      exclude[DirectMissingMethodProblem]("sbt.package.toFn1"),
+    )
   )
   .configure(addSbtCompilerBridge)
 
@@ -461,14 +473,6 @@ lazy val vscodePlugin = (project in file("vscode-sbt-scala"))
     }
   )
 
-lazy val sbtIgnoredProblems = {
-  Seq(
-    // Added more items to Import trait.
-    exclude[ReversedMissingMethodProblem]("sbt.Import.sbt$Import$_setter_$WatchSource_="),
-    exclude[ReversedMissingMethodProblem]("sbt.Import.WatchSource")
-  )
-}
-
 def scriptedTask: Def.Initialize[InputTask[Unit]] = Def.inputTask {
   val result = scriptedSource(dir => (s: State) => Scripted.scriptedParser(dir)).parsed
   // publishLocalBinAll.value // TODO: Restore scripted needing only binary jars.

internal/util-collection/src/main/scala/sbt/internal/util/TypeFunctions.scala

@@ -29,10 +29,6 @@ trait TypeFunctions {
         def apply[T](mg: M[G[T]]): N[G[T]] = f(mg)
     } */
 
-  implicit def toFn1[A, B](f: A => B): Fn1[A, B] = new Fn1[A, B] {
-    def ∙[C](g: C => A) = f compose g
-  }
-
   type Endo[T] = T => T
   type ~>|[A[_], B[_]] = A ~> Compose[Option, B]#Apply
 }
@@ -52,7 +48,3 @@ object ~> {
   val Id: Id ~> Id = new (Id ~> Id) { def apply[T](a: T): T = a }
   implicit def tcIdEquals: (Id ~> Id) = Id
 }
-
-trait Fn1[A, B] {
-  def ∙[C](g: C => A): C => B
-}

sbt/src/main/scala/Import.scala

@@ -133,7 +133,6 @@ trait Import {
   type FeedbackProvidedException = sbt.internal.util.FeedbackProvidedException
   type FilePosition = sbt.internal.util.FilePosition
   type FilterLogger = sbt.internal.util.FilterLogger
-  type Fn1[A, B] = sbt.internal.util.Fn1[A, B]
   val FullLogger = sbt.internal.util.FullLogger
   type FullLogger = sbt.internal.util.FullLogger
   val FullReader = sbt.internal.util.FullReader

tasks-standard/src/main/scala/sbt/std/System.scala

@@ -48,7 +48,7 @@ object Transform {
       case Pure(eval, _)       => uniform(Nil)(_ => Right(eval()))
       case m: Mapped[t, k]     => toNode[t, k](m.in)(right ∙ m.f)(m.alist)
       case m: FlatMapped[t, k] => toNode[t, k](m.in)(left ∙ m.f)(m.alist)
-      case DependsOn(in, deps) => uniform(existToAny(deps))(const(Left(in)) ∙ all)
+      case DependsOn(in, deps) => uniform(existToAny(deps))(const(Left(in)) compose all)
       case Join(in, f)         => uniform(in)(f)
     }
     def inline[T](t: Task[T]) = t.work match {