Fix toFunctionType to handle erased function types

Author: nicolasstucki

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

@@ -1475,6 +1475,7 @@ class Definitions {
   def PolyFunctionType = PolyFunctionClass.typeRef
 
   lazy val ErasedFunctionClass = requiredClass("scala.runtime.ErasedFunction")
+  def ErasedFunctionType = ErasedFunctionClass.typeRef
 
   /** If `cls` is a class in the scala package, its name, otherwise EmptyTypeName */
   def scalaClassName(cls: Symbol)(using Context): TypeName = cls.denot match

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

@@ -1875,7 +1875,7 @@ object Types {
      *  @param alwaysDependent if true, always create a dependent function type.
      */
     def toFunctionType(isJava: Boolean, dropLast: Int = 0, alwaysDependent: Boolean = false)(using Context): Type = this match {
-      case mt: MethodType if !mt.isParamDependent =>
+      case mt: MethodType if !mt.isParamDependent && !mt.hasErasedParams =>
         val formals1 = if (dropLast == 0) mt.paramInfos else mt.paramInfos dropRight dropLast
         val isContextual = mt.isContextualMethod && !ctx.erasedTypes
         val result1 = mt.nonDependentResultApprox match {
@@ -1888,6 +1888,9 @@ object Types {
         if alwaysDependent || mt.isResultDependent then
           RefinedType(funType, nme.apply, mt)
         else funType
+      case mt: MethodType if !mt.isParamDependent =>
+        assert(mt.hasErasedParams)
+        RefinedType(defn.ErasedFunctionType, nme.apply, mt)
       case poly @ PolyType(_, mt: MethodType) if !mt.isParamDependent =>
         RefinedType(defn.PolyFunctionType, nme.apply, poly)
     }

tests/run-custom-args/erased/quotes-reflection.check

@@ -4,7 +4,7 @@ method m2: (i: scala.Int) isGiven=false isImplicit=false erasedArgs=List(true)
 method m3: (i: scala.Int, j: scala.Int) isGiven=false isImplicit=false erasedArgs=List(false, true)
 method m4: (i: EC) isGiven=false isImplicit=false erasedArgs=List(true)
 val l1: scala.ContextFunction1[scala.Int, scala.Int]
-val l2: scala.runtime.ErasedFunction with apply: (x$0: scala.Int @scala.annotation.internal.ErasedParam) isImplicit=false erasedParams=List(true)
-val l3: scala.runtime.ErasedFunction with apply: (x$0: scala.Int @scala.annotation.internal.ErasedParam) isImplicit=true erasedParams=List(true)
-val l4: scala.runtime.ErasedFunction with apply: (x$0: scala.Int, x$1: scala.Int @scala.annotation.internal.ErasedParam) isImplicit=false erasedParams=List(false, true)
-val l5: scala.runtime.ErasedFunction with apply: (x$0: EC @scala.annotation.internal.ErasedParam) isImplicit=false erasedParams=List(true)
+val l2: scala.runtime.ErasedFunction with apply: (x: scala.Int @scala.annotation.internal.ErasedParam) isImplicit=false erasedParams=List(true)
+val l3: scala.runtime.ErasedFunction with apply: (x: scala.Int @scala.annotation.internal.ErasedParam) isImplicit=true erasedParams=List(true)
+val l4: scala.runtime.ErasedFunction with apply: (x: scala.Int, y: scala.Int @scala.annotation.internal.ErasedParam) isImplicit=false erasedParams=List(false, true)
+val l5: scala.runtime.ErasedFunction with apply: (x: EC @scala.annotation.internal.ErasedParam) isImplicit=false erasedParams=List(true)