Fix SimpleIdentitySet#map

Previously, the result of a map could contain duplicates.

I verified that with the current code base this could cause problems only for
capture checking.

Author: odersky

compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala

@@ -14,7 +14,10 @@ abstract class SimpleIdentitySet[+Elem <: AnyRef] {
   def contains[E >: Elem <: AnyRef](x: E): Boolean
   def foreach(f: Elem => Unit): Unit
   def exists[E >: Elem <: AnyRef](p: E => Boolean): Boolean
-  def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B]
+  def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
+    var acc: SimpleIdentitySet[B] = SimpleIdentitySet.empty
+    foreach(x => acc += f(x))
+    acc
   def /: [A, E >: Elem <: AnyRef](z: A)(f: (A, E) => A): A
   def toList: List[Elem]
   def iterator: Iterator[Elem]
@@ -63,7 +66,7 @@ object SimpleIdentitySet {
     def contains[E <: AnyRef](x: E): Boolean = false
     def foreach(f: Nothing => Unit): Unit = ()
     def exists[E <: AnyRef](p: E => Boolean): Boolean = false
-    def map[B <: AnyRef](f: Nothing => B): SimpleIdentitySet[B] = empty
+    override def map[B <: AnyRef](f: Nothing => B): SimpleIdentitySet[B] = empty
     def /: [A, E <: AnyRef](z: A)(f: (A, E) => A): A = z
     def toList = Nil
     def iterator = Iterator.empty
@@ -79,7 +82,7 @@ object SimpleIdentitySet {
     def foreach(f: Elem => Unit): Unit = f(x0.asInstanceOf[Elem])
     def exists[E >: Elem <: AnyRef](p: E => Boolean): Boolean =
       p(x0.asInstanceOf[E])
-    def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
+    override def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
       Set1(f(x0.asInstanceOf[Elem]))
     def /: [A, E >: Elem <: AnyRef](z: A)(f: (A, E) => A): A =
       f(z, x0.asInstanceOf[E])
@@ -99,8 +102,10 @@ object SimpleIdentitySet {
     def foreach(f: Elem => Unit): Unit = { f(x0.asInstanceOf[Elem]); f(x1.asInstanceOf[Elem]) }
     def exists[E >: Elem <: AnyRef](p: E => Boolean): Boolean =
       p(x0.asInstanceOf[E]) || p(x1.asInstanceOf[E])
-    def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
-      Set2(f(x0.asInstanceOf[Elem]), f(x1.asInstanceOf[Elem]))
+    override def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
+      val y0 = f(x0.asInstanceOf[Elem])
+      val y1 = f(x1.asInstanceOf[Elem])
+      if y0 eq y1 then Set1(y0) else Set2(y0, y1)
     def /: [A, E >: Elem <: AnyRef](z: A)(f: (A, E) => A): A =
       f(f(z, x0.asInstanceOf[E]), x1.asInstanceOf[E])
     def toList = x0.asInstanceOf[Elem] :: x1.asInstanceOf[Elem] :: Nil
@@ -133,8 +138,12 @@ object SimpleIdentitySet {
     }
     def exists[E >: Elem <: AnyRef](p: E => Boolean): Boolean =
       p(x0.asInstanceOf[E]) || p(x1.asInstanceOf[E]) || p(x2.asInstanceOf[E])
-    def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
-      Set3(f(x0.asInstanceOf[Elem]), f(x1.asInstanceOf[Elem]), f(x2.asInstanceOf[Elem]))
+    override def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
+      val y0 = f(x0.asInstanceOf[Elem])
+      val y1 = f(x1.asInstanceOf[Elem])
+      val y2 = f(x2.asInstanceOf[Elem])
+      if (y0 ne y1) && (y0 ne y2) && (y1 ne y2) then Set3(y0, y1, y2)
+      else super.map(f)
     def /: [A, E >: Elem <: AnyRef](z: A)(f: (A, E) => A): A =
       f(f(f(z, x0.asInstanceOf[E]), x1.asInstanceOf[E]), x2.asInstanceOf[E])
     def toList = x0.asInstanceOf[Elem] :: x1.asInstanceOf[Elem] :: x2.asInstanceOf[Elem] :: Nil
@@ -182,8 +191,6 @@ object SimpleIdentitySet {
     }
     def exists[E >: Elem <: AnyRef](p: E => Boolean): Boolean =
       xs.asInstanceOf[Array[E]].exists(p)
-    def map[B <: AnyRef](f: Elem => B): SimpleIdentitySet[B] =
-      SetN(xs.map(x => f(x.asInstanceOf[Elem]).asInstanceOf[AnyRef]))
     def /: [A, E >: Elem <: AnyRef](z: A)(f: (A, E) => A): A =
       xs.asInstanceOf[Array[E]].foldLeft(z)(f)
     def toList: List[Elem] = {