Remove tvars introduced while testing normalizedCompatible

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -71,6 +71,10 @@ object ProtoTypes {
                    |constraint was: ${ctx.typerState.constraint}
                    |constraint now: ${newctx.typerState.constraint}""")
             if result && (ctx.typerState.constraint ne newctx.typerState.constraint) then
+              val tvars = (newctx.typerState.ownedVars -- ctx.typerState.ownedVars).toList
+              inContext(newctx):
+                Inferencing.instantiateSelected(tp, tvars)
+                for tvar <- tvars do if !tvar.isInstantiated then tvar.instantiate(fromBelow = false)
               newctx.typerState.commit()
             result
           case _ => testCompat

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3557,6 +3557,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
   protected def simplify(tree: Tree, pt: Type, locked: TypeVars)(using Context): tree.type =
     if !tree.denot.isOverloaded then // for overloaded trees: resolve overloading before simplifying
       if !tree.tpe.widen.isInstanceOf[MethodOrPoly] // wait with simplifying until method is fully applied
+         && !tree.tpe.match { case defn.PolyFunctionOf(_) => true case _ => false } // ... or polyfunction is fully applied
          || tree.isDef                              // ... unless tree is a definition
       then
         interpolateTypeVars(tree, pt, locked)

tests/pos/interleaving-overload.cleanup.scala

@@ -0,0 +1,10 @@
+// Justifies the need to add defn.PolyFunctionOf in simplify
+// Without, the TypeVar for the U in fn's lambda
+// replaces the TypeParamRef U, in simplify.
+class B[U]
+class Test():
+  def fn[T]: [U] => Int => B[U] = [U] => (x: Int) => new B[U]()
+  def test(): Unit =
+    fn(1)
+    fn(2)
+    ()

tests/pos/zipped.min.scala

@@ -0,0 +1,15 @@
+// Justifies the need for TypeApply in tryInsertImplicitOnQualifier
+// after failing ys.map[?B, C] using Zipped2's map
+// we want to try ys.map[?B] using Coll's map, after toColl
+final class Coll[+A]:
+  def map[B](f: A => B): Coll[B] = new Coll[B]
+  def lazyZip[B](that: Coll[B]): Zipped2[A, B] = new Zipped2[A, B](this, that)
+final class Zipped2[+X, +Y](xs: Coll[X], ys: Coll[Y]):
+  def map[B, C](f: (X, Y) => B): Coll[C] = new Coll[C]
+object Zipped2:
+  import scala.language.implicitConversions
+  implicit def toColl[X, Y](zipped2: Zipped2[X, Y]): Coll[(X, Y)] = new Coll[(X, Y)]
+class Test:
+  def test(xs: Coll[Int]): Unit =
+    val ys = xs.lazyZip(xs)
+    ys.map((x: (Int, Int)) => x._1 + x._2)