Remove all warnings from collectionProj

build.sbt

@@ -157,6 +157,11 @@ val collectionProj = (project in file("internal") / "util-collection")
       exclude[MissingClassProblem]("sbt.internal.util.Fn1"),
       exclude[DirectMissingMethodProblem]("sbt.internal.util.TypeFunctions.toFn1"),
       exclude[DirectMissingMethodProblem]("sbt.internal.util.Types.toFn1"),
+
+      // Instead of defining foldr in KList & overriding in KCons,
+      // it's now abstract in KList and defined in both KCons & KNil.
+      exclude[FinalMethodProblem]("sbt.internal.util.KNil.foldr"),
+      exclude[DirectAbstractMethodProblem]("sbt.internal.util.KList.foldr"),
     ),
   )
   .configure(addSbtUtilPosition)

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

@@ -7,6 +7,8 @@
 
 package sbt.internal.util
 
+import scala.collection.JavaConverters._
+
 /** A mutable set interface that uses object identity to test for set membership.*/
 trait IDSet[T] {
   def apply(t: T): Boolean
@@ -41,7 +43,7 @@ object IDSet {
     def +=(t: T) = { backing.put(t, Dummy); () }
     def ++=(t: Iterable[T]) = t foreach +=
     def -=(t: T) = if (backing.remove(t) eq null) false else true
-    def all = collection.JavaConverters.collectionAsScalaIterable(backing.keySet)
+    def all = backing.keySet.asScala
     def toList = all.toList
     def isEmpty = backing.isEmpty
 

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

@@ -18,7 +18,7 @@ sealed trait KList[+M[_]] {
   def transform[N[_]](f: M ~> N): Transform[N]
 
   /** Folds this list using a function that operates on the homogeneous type of the elements of this list. */
-  def foldr[B](f: (M[_], B) => B, init: B): B = init // had trouble defining it in KNil
+  def foldr[B](f: (M[_], B) => B, init: B): B
 
   /** Applies `f` to the elements of this list in the applicative functor defined by `ap`. */
   def apply[N[x] >: M[x], Z](f: Transform[Id] => Z)(implicit ap: Applicative[N]): N[Z]
@@ -54,13 +54,14 @@ final case class KCons[H, +T <: KList[M], +M[_]](head: M[H], tail: T) extends KL
   override def foldr[B](f: (M[_], B) => B, init: B): B = f(head, tail.foldr(f, init))
 }
 
-sealed abstract class KNil extends KList[Nothing] {
+sealed abstract class KNil extends KList[NothingK] {
   final type Transform[N[_]] = KNil
-  final def transform[N[_]](f: Nothing ~> N): Transform[N] = KNil
+  final def transform[N[_]](f: NothingK ~> N): Transform[N] = KNil
+  final def foldr[B](f: (NothingK[_], B) => B, init: B): B = init
   final def toList = Nil
   final def apply[N[x], Z](f: KNil => Z)(implicit ap: Applicative[N]): N[Z] = ap.pure(f(KNil))
 
-  final def traverse[N[_], P[_]](f: Nothing ~> (N ∙ P)#l)(implicit np: Applicative[N]): N[KNil] =
+  final def traverse[N[_], P[_]](f: NothingK ~> (N ∙ P)#l)(implicit np: Applicative[N]): N[KNil] =
     np.pure(KNil)
 }
 

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

@@ -65,7 +65,7 @@ object Signals {
 }
 
 // Must only be referenced using a
-//   try { } catch { case e: LinkageError => ... }
+//   try { } catch { case _: LinkageError => ... }
 // block to
 private final class Signals0 {
   def supported(signal: String): Boolean = {

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

@@ -9,6 +9,7 @@ package sbt.internal.util
 
 trait TypeFunctions {
   type Id[X] = X
+  type NothingK[X] = Nothing
   sealed trait Const[A] { type Apply[B] = A }
   sealed trait ConstK[A] { type l[L[x]] = A }
   sealed trait Compose[A[_], B[_]] { type Apply[T] = A[B[T]] }

internal/util-collection/src/test/scala/SettingsTest.scala

@@ -7,8 +7,7 @@
 
 package sbt.internal.util
 
-import org.scalacheck._
-import Prop._
+import org.scalacheck._, Prop._
 
 object SettingsTest extends Properties("settings") {
   val settingsExample: SettingsExample = SettingsExample()
@@ -160,7 +159,7 @@ object SettingsTest extends Properties("settings") {
   final def checkCircularReferences(intermediate: Int): Prop = {
     val ccr = new CCR(intermediate)
     try { evaluate(setting(chk, ccr.top) :: Nil); false } catch {
-      case e: java.lang.Exception => true
+      case _: java.lang.Exception => true
     }
   }
 
@@ -197,18 +196,18 @@ object SettingsTest extends Properties("settings") {
 
   def evaluate(settings: Seq[Setting[_]]): Settings[Scope] =
     try { make(settings)(delegates, scopeLocal, showFullKey) } catch {
-      case e: Throwable => e.printStackTrace; throw e
+      case e: Throwable => e.printStackTrace(); throw e
     }
 }
 // This setup is a workaround for module synchronization issues
 final class CCR(intermediate: Int) {
   import SettingsTest.settingsExample._
-  lazy val top = iterate(value(intermediate), intermediate)
-  def iterate(init: Initialize[Int], i: Int): Initialize[Int] =
+  lazy val top = iterate(value(intermediate))
+  def iterate(init: Initialize[Int]): Initialize[Int] =
     bind(init) { t =>
       if (t <= 0)
         top
       else
-        iterate(value(t - 1), t - 1)
+        iterate(value(t - 1))
     }
 }