use TypeAccumulator

Author: Alex1005a

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

@@ -4367,21 +4367,18 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             val pt1 = pt.deepenProtoTrans
             val approxPt = withMode(Mode.TypevarsMissContext):
               wildApprox(pt1)
-            var formalConstrained = false
-            val tm = new TypeMap:
-              def apply(t: Type): Type = t match
-                case tvar: TypeVar =>
-                  formalConstrained |= ctx.typerState.constraint.contains(tvar) || tvar.instanceOpt.isInstanceOf[TypeVar]
-                  tvar
-                case _ =>
-                  if formalConstrained then t
-                  else mapOver(t)
-            tm(formal)
+            val containsUninst = new TypeAccumulator[Boolean]:
+              def apply(need: Boolean, tp: Type): Boolean =
+                need || tp.match
+                  case tvar: TypeVar =>
+                    ctx.typerState.constraint.contains(tvar) || tvar.instanceOpt.isInstanceOf[TypeVar]
+                  case _ =>
+                    foldOver(need, tp)
             if (pt1 `ne` pt)
               && (pt1 ne sharpenedPt)
               && (AvoidWildcardsMap()(approxPt) `eq` approxPt)
               && !isFullyDefined(formal, ForceDegree.none)
-              && !formalConstrained then
+              && !containsUninst(false, formal) then
               constrainResult(tree.symbol, wtp, pt1)
             val arg = inferImplicitArg(formal, tree.span.endPos)