Remove tvars introduced while testing normalizedCompatible

Author: dwijnand

compiler/src/dotty/tools/dotc/core/TyperState.scala

@@ -139,14 +139,15 @@ class TyperState() {
   def uncommittedAncestor: TyperState =
     if (isCommitted && previous != null) previous.uncheckedNN.uncommittedAncestor else this
 
-  /** Commit typer state so that its information is copied into current typer state
+  /** Commit `this` typer state by copying information into the current typer state,
+   *  where "current" means contextual, so meaning `ctx.typerState`.
    *  In addition (1) the owning state of undetermined or temporarily instantiated
    *  type variables changes from this typer state to the current one. (2) Variables
    *  that were temporarily instantiated in the current typer state are permanently
    *  instantiated instead.
    *
    *  A note on merging: An interesting test case is isApplicableSafe.scala. It turns out that this
-   *  requires a context merge using the new `&' operator. Sequence of actions:
+   *  requires a context merge using the new `&` operator. Sequence of actions:
    *  1) Typecheck argument in typerstate 1.
    *  2) Cache argument.
    *  3) Evolve same typer state (to typecheck other arguments, say)

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -4879,7 +4879,7 @@ object Types extends TypeUtils {
     def origin: TypeParamRef = currentOrigin
 
     /** Set origin to new parameter. Called if we merge two conflicting constraints.
-     *  See OrderingConstraint#merge, OrderingConstraint#rename
+     *  See OrderingConstraint#merge
      */
     def setOrigin(p: TypeParamRef) = currentOrigin = p
 

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

@@ -71,7 +71,8 @@ object ProtoTypes {
                    |constraint was: ${ctx.typerState.constraint}
                    |constraint now: ${newctx.typerState.constraint}""")
             if result && (ctx.typerState.constraint ne newctx.typerState.constraint) then
-              newctx.typerState.commit()
+              newctx.typerState.gc()     // Remove any type lambdas and tvars added via testCompat
+              newctx.typerState.commit() // Commit the rest of the typer state information
             result
           case _ => testCompat
       else explore(testCompat)

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)