Add missing dealias in isContextFunctionRef

Fixes #15738

Author: odersky

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

@@ -3704,7 +3704,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         missingArgs(wtp)
     }
 
-    def isContextFunctionRef(wtp: Type): Boolean = wtp match {
+    def isContextFunctionRef(wtp: Type): Boolean = wtp.dealias match {
       case RefinedType(parent, nme.apply, _) =>
         isContextFunctionRef(parent) // apply refinements indicate a dependent CFT
       case _ =>

tests/pos/i15738.scala

@@ -0,0 +1,16 @@
+object Test {
+  trait Transaction
+  type Transactional[T] = (Transaction) ?=> T
+
+  def ff(x: Int): Transactional[Int] = {
+    //summon[Transaction]
+    x
+  }
+
+  def fff(x: Int): Transactional[Int] = {
+    //summon[Transaction]
+    val x1 = ff(x)
+    x1
+  }
+
+}