Merge pull request #15742 from dotty-staging/fix-15738

Author: dwijnand

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

@@ -3730,16 +3730,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         missingArgs(wtp)
     }
 
-    def isContextFunctionRef(wtp: Type): Boolean = wtp match {
-      case RefinedType(parent, nme.apply, _) =>
-        isContextFunctionRef(parent) // apply refinements indicate a dependent CFT
-      case _ =>
-        val underlying = wtp.underlyingClassRef(refinementOK = false) // other refinements are not OK
-        defn.isContextFunctionClass(underlying.classSymbol)
-    }
-
     def adaptNoArgsOther(wtp: Type, functionExpected: Boolean): Tree = {
-      val implicitFun = isContextFunctionRef(wtp) && !untpd.isContextualClosure(tree)
+      val implicitFun = defn.isContextFunctionType(wtp) && !untpd.isContextualClosure(tree)
       def caseCompanion =
           functionExpected &&
           tree.symbol.is(Module) &&

tests/pos/i15738.scala

@@ -0,0 +1,16 @@
+object Test {
+  trait Transaction
+  type Transactional[T] = (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
+  }
+
+}