Remove tvars introduced while testing normalizedCompatible (#21466)

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

@@ -4124,6 +4124,7 @@ object Types extends TypeUtils {
     protected def prefixString: String = companion.prefixString
   }
 
+  // Actually.. not cached.  MethodOrPoly are `UncachedGroundType`s.
   final class CachedMethodType(paramNames: List[TermName])(paramInfosExp: MethodType => List[Type], resultTypeExp: MethodType => Type, val companion: MethodTypeCompanion)
     extends MethodType(paramNames)(paramInfosExp, resultTypeExp)
 
@@ -4884,7 +4885,7 @@ 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/printing/Formatting.scala

@@ -184,7 +184,7 @@ object Formatting {
     * The idea is to do this for known cases that are useful and then fall back
     * on regular syntax highlighting for the cases which are unhandled.
     *
-    * Please not that if used in combination with `disambiguateTypes` the
+    * Please note that if used in combination with `disambiguateTypes` the
     * correct `Context` for printing should also be passed when calling the
     * method.
     *

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -253,7 +253,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
           toTextCapturing(parent, refsText, "") ~ Str("R").provided(printDebug)
         else toText(parent)
       case tp: PreviousErrorType if ctx.settings.XprintTypes.value =>
-        "<error>" // do not print previously reported error message because they may try to print this error type again recuresevely
+        "<error>" // do not print previously reported error message because they may try to print this error type again recursively
       case tp: ErrorType =>
         s"<error ${tp.msg.message}>"
       case tp: WildcardType =>

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

@@ -71,6 +71,13 @@ object ProtoTypes {
                    |constraint was: ${ctx.typerState.constraint}
                    |constraint now: ${newctx.typerState.constraint}""")
             if result && (ctx.typerState.constraint ne newctx.typerState.constraint) then
+              // Remove all type lambdas and tvars introduced by testCompat
+              for tvar <- newctx.typerState.ownedVars do
+                inContext(newctx):
+                  if !tvar.isInstantiated then
+                    tvar.instantiate(fromBelow = false) // any direction
+
+              // commit any remaining changes in typer state
               newctx.typerState.commit()
             result
           case _ => testCompat

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

@@ -360,20 +360,21 @@ trait TypeAssigner {
                 resultType1)
             }
           }
+          else if !args.hasSameLengthAs(paramNames) then
+            wrongNumberOfTypeArgs(fn.tpe, pt.typeParams, args, tree.srcPos)
           else {
             // Make sure arguments don't contain the type `pt` itself.
-            // make a copy of the argument if that's the case.
+            // Make a copy of `pt` if that's the case.
             // This is done to compensate for the fact that normally every
             // reference to a polytype would have to be a fresh copy of that type,
             // but we want to avoid that because it would increase compilation cost.
             // See pos/i6682a.scala for a test case where the defensive copying matters.
-            val ensureFresh = new TypeMap with CaptureSet.IdempotentCaptRefMap:
-              def apply(tp: Type) = mapOver(
-                if tp eq pt then pt.newLikeThis(pt.paramNames, pt.paramInfos, pt.resType)
-                else tp)
-            val argTypes = args.tpes.mapConserve(ensureFresh)
-            if (argTypes.hasSameLengthAs(paramNames)) pt.instantiate(argTypes)
-            else wrongNumberOfTypeArgs(fn.tpe, pt.typeParams, args, tree.srcPos)
+            val needsFresh = new ExistsAccumulator(_ eq pt, StopAt.None, forceLazy = false)
+            val argTypes = args.tpes
+            val pt1 = if argTypes.exists(needsFresh(false, _)) then
+              pt.newLikeThis(pt.paramNames, pt.paramInfos, pt.resType)
+            else pt
+            pt1.instantiate(argTypes)
           }
         }
       case err: ErrorType =>

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

@@ -4757,7 +4757,29 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
               var typeArgs = tree match
                 case Select(qual, nme.CONSTRUCTOR) => qual.tpe.widenDealias.argTypesLo.map(TypeTree(_))
                 case _ => Nil
-              if typeArgs.isEmpty then typeArgs = constrained(poly, tree)._2.map(_.wrapInTypeTree(tree))
+              if typeArgs.isEmpty then
+                val poly1 = tree match
+                  case Select(qual, nme.apply) => qual.tpe.widen match
+                    case defn.PolyFunctionOf(_) =>
+                      // Given a poly function, like the one in i6682a:
+                      //    val v = [T] => (y:T) => (x:y.type) => 3
+                      // It's possible to apply `v(v)` which extends to:
+                      //    v.apply[?T](v)
+                      // Requiring the circular constraint `v <: ?T`,
+                      // (because type parameter T occurs in v's type).
+                      // So we create a fresh copy of the outer
+                      // poly method type, so we now extend to:
+                      //    v.apply[?T'](v)
+                      // Where `?T'` is a type var for a T' type parameter,
+                      // leading to the non-circular `v <: ?T'` constraint.
+                      //
+                      // This also happens in `assignType(tree: untpd.TypeApply, ..)`
+                      // to avoid any type arguments, containing the type lambda,
+                      // being applied to the very same type lambda.
+                      poly.newLikeThis(poly.paramNames, poly.paramInfos, poly.resType)
+                    case _ => poly
+                  case _ => poly
+                typeArgs = constrained(poly1, tree)._2.map(_.wrapInTypeTree(tree))
               convertNewGenericArray(readapt(tree.appliedToTypeTrees(typeArgs)))
         case wtp =>
           val isStructuralCall = wtp.isValueType && isStructuralTermSelectOrApply(tree)

tests/pos/interleaving-overload.cleanup.scala

@@ -0,0 +1,9 @@
+// A minimisation of interleaving-overload
+// Used while developing the tvar/tl clearnup in normalizedCompatible
+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)