Fix scala#11318: properly detect enclosing extension methods from a p…

…olyfunction.

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

@@ -1130,6 +1130,9 @@ object SymDenotations {
       if (cls.effectiveName == name || !cls.exists) cls else cls.owner.enclosingClassNamed(name)
     }
 
+    final def isPolyFunction(using Context): Boolean =
+      this.asInstanceOf[ClassDenotation].parentSyms.contains(defn.PolyFunctionClass)
+
     /** The closest enclosing method containing this definition.
      *  A local dummy owner is mapped to the primary constructor of the class.
      */
@@ -1144,7 +1147,7 @@ object SymDenotations {
      */
     final def enclosingExtensionMethod(using Context): Symbol =
       if this.is(ExtensionMethod) then symbol
-      else if this.isClass then NoSymbol
+      else if this.isClass && !this.isPolyFunction then NoSymbol
       else if this.exists then owner.enclosingExtensionMethod
       else NoSymbol
 

tests/pos/i11318a.scala

@@ -0,0 +1,4 @@
+extension(a: Int)
+  def b: Int = ???
+  def h: Unit =
+    [A] => (r: Int) => b

tests/pos/i11318b.scala

@@ -0,0 +1,13 @@
+type FunctionK[A[_], B[_]] = [Z] => A[Z] => B[Z]
+type ~>:[A[_], B[_]] = FunctionK[A, B]
+
+trait RepresentableK[F[_[_], _]]:
+  type RepresentationK[_]
+
+  def tabulateK[A[_], C](f: RepresentationK ~>: A): F[A, C]
+
+  extension[A[_], C](fa: F[A, C])
+    def indexK: RepresentationK ~>: A
+
+    def mapK[B[_]] (f: A ~>: B): F[B, C] =
+      tabulateK([Z] => (r: RepresentationK[Z]) => f(indexK(r)))