Fix #2146: Make nested implicit function types work

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

@@ -283,7 +283,7 @@ object NameKinds {
   val ProtectedAccessorName = new PrefixNameKind(PROTECTEDACCESSOR, "protected$")
   val ProtectedSetterName = new PrefixNameKind(PROTECTEDSETTER, "protected$set") // dubious encoding, kept for Scala2 compatibility
   val AvoidClashName = new SuffixNameKind(AVOIDCLASH, "$_avoid_name_clash_$")
-  val DirectName = new SuffixNameKind(DIRECT, "$direct")
+  val DirectMethodName = new SuffixNameKind(DIRECT, "$direct") { override def definesNewName = true }
   val FieldName = new SuffixNameKind(FIELD, "$$local")
   val ExtMethName = new SuffixNameKind(EXTMETH, "$extension")
   val ModuleVarName = new SuffixNameKind(OBJECTVAR, "$module")

compiler/src/dotty/tools/dotc/transform/ShortcutImplicits.scala

@@ -11,7 +11,7 @@ import core.Decorators._
 import core.StdNames.nme
 import core.Names._
 import core.NameOps._
-import core.NameKinds.DirectName
+import core.NameKinds.DirectMethodName
 import ast.Trees._
 import ast.tpd
 import collection.mutable
@@ -77,6 +77,7 @@ class ShortcutImplicits extends MiniPhase with IdentityDenotTransformer { thisTr
     private def shouldBeSpecialized(sym: Symbol)(implicit ctx: Context) =
       sym.is(Method, butNot = Accessor) &&
       defn.isImplicitFunctionType(sym.info.finalResultType) &&
+      !sym.isAnonymousFunction &&
       (specializeMonoTargets || !sym.isEffectivelyFinal || sym.allOverriddenSymbols.nonEmpty)
 
     /** @pre    The type's final result type is an implicit function type `implicit Ts => R`.
@@ -92,7 +93,7 @@ class ShortcutImplicits extends MiniPhase with IdentityDenotTransformer { thisTr
     /** A new `m$direct` method to accompany the given method `m` */
     private def newDirectMethod(sym: Symbol)(implicit ctx: Context): Symbol = {
       val direct = sym.copy(
-        name = DirectName(sym.name.asTermName).asInstanceOf[sym.ThisName],
+        name = DirectMethodName(sym.name.asTermName).asInstanceOf[sym.ThisName],
         flags = sym.flags | Synthetic,
         info = directInfo(sym.info))
       if (direct.allOverriddenSymbols.isEmpty) direct.resetFlag(Override)
@@ -104,14 +105,13 @@ class ShortcutImplicits extends MiniPhase with IdentityDenotTransformer { thisTr
      */
     private def directMethod(sym: Symbol)(implicit ctx: Context): Symbol =
       if (sym.owner.isClass) {
-        val direct = sym.owner.info.member(DirectName(sym.name.asTermName))
+        val direct = sym.owner.info.member(DirectMethodName(sym.name.asTermName))
           .suchThat(_.info matches directInfo(sym.info)).symbol
         if (direct.maybeOwner == sym.owner) direct
         else newDirectMethod(sym).enteredAfter(thisTransform)
       }
       else directMeth.getOrElseUpdate(sym, newDirectMethod(sym))
 
-
     /** Transform `qual.apply` occurrences according to rewrite rule (2) above */
     override def transformSelect(tree: Select)(implicit ctx: Context, info: TransformerInfo) =
       if (tree.name == nme.apply &&
@@ -122,7 +122,7 @@ class ShortcutImplicits extends MiniPhase with IdentityDenotTransformer { thisTr
           case TypeApply(fn, args) => cpy.TypeApply(tree)(directQual(fn), args)
           case Block(stats, expr)  => cpy.Block(tree)(stats, directQual(expr))
           case tree: RefTree =>
-            cpy.Ref(tree)(DirectName(tree.name.asTermName))
+            cpy.Ref(tree)(DirectMethodName(tree.name.asTermName))
               .withType(directMethod(tree.symbol).termRef)
         }
         directQual(tree.qualifier)
@@ -157,8 +157,8 @@ class ShortcutImplicits extends MiniPhase with IdentityDenotTransformer { thisTr
 
         val (remappedCore, fwdClosure) = splitClosure(mdef.rhs)
         val originalDef = cpy.DefDef(mdef)(rhs = fwdClosure)
-        val directDef = polyDefDef(direct.asTerm, remappedCore)
-        Thicket(originalDef, directDef)
+        val directDef = transformDefDef(polyDefDef(direct.asTerm, remappedCore))
+        flatTree(List(originalDef, directDef))
       }
       else mdef
     }

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

@@ -422,8 +422,8 @@ object ProtoTypes {
 
   /** The normalized form of a type
    *   - unwraps polymorphic types, tracking their parameters in the current constraint
-   *   - skips implicit parameters; if result type depends on implicit parameter,
-   *     replace with Wildcard.
+   *   - skips implicit parameters of methods and functions;
+   *     if result type depends on implicit parameter, replace with fresh type dependent parameter.
    *   - converts non-dependent method types to the corresponding function types
    *   - dereferences parameterless method types
    *   - dereferences nullary method types provided the corresponding function type
@@ -437,9 +437,10 @@ object ProtoTypes {
    */
   def normalize(tp: Type, pt: Type)(implicit ctx: Context): Type = Stats.track("normalize") {
     tp.widenSingleton match {
-      case poly: PolyType => normalize(constrained(poly).resultType, pt)
+      case poly: PolyType =>
+        normalize(constrained(poly).resultType, pt)
       case mt: MethodType =>
-        if (mt.isImplicit) resultTypeApprox(mt)
+        if (mt.isImplicit) normalize(resultTypeApprox(mt), pt)
         else if (mt.isDependent) tp
         else {
           val rt = normalize(mt.resultType, pt)
@@ -451,8 +452,11 @@ object ProtoTypes {
               if (mt.paramInfos.nonEmpty || ft <:< pt) ft else rt
           }
         }
-      case et: ExprType => et.resultType
-      case _ => tp
+      case et: ExprType =>
+        normalize(et.resultType, pt)
+      case wtp =>
+        if (defn.isImplicitFunctionType(wtp)) normalize(wtp.dealias.argInfos.last, pt)
+        else tp
     }
   }
 

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

@@ -1582,7 +1582,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val paramTypes = formals.map(fullyDefinedType(_, "implicit function parameter", tree.pos))
     val ifun = desugar.makeImplicitFunction(paramTypes, tree)
     typr.println(i"make implicit function $tree / $pt ---> $ifun")
-    typedUnadapted(ifun)
+    typed(ifun, pt)
   }
 
   def typed(tree: untpd.Tree, pt: Type = WildcardType)(implicit ctx: Context): Tree = /*>|>*/ ctx.traceIndented (i"typing $tree", typr, show = true) /*<|<*/ {

tests/neg/i2146.scala

@@ -0,0 +1,8 @@
+object Test {
+  case class A()
+  case class B()
+
+  def foo[A, B]: implicit A => implicit B => Int = { implicit b: B =>
+    42 // error: found Int, required: implicit A => implicit B => Int
+  }
+}

tests/pos/i2146.check

@@ -0,0 +1,9 @@
+(A(),B())
+(A(),B())
+(A(),B())
+A()
+(A(),B())
+(A(),B())
+(A(),B())
+(A(),B())
+(A(),B())

tests/pos/i2146.scala

@@ -0,0 +1,32 @@
+object Test {
+  case class A()
+  case class B()
+
+  def simple[A]: implicit A => A = implicitly[A]
+
+  def foo[A, B]: implicit A => implicit B => (A, B) =
+    (implicitly[A], implicitly[B])
+
+  def bar[A, B]: implicit A => implicit B => (A, B) = { implicit a: A =>
+    (implicitly[A], implicitly[B])
+  }
+
+  implicit val a: A = A()
+  implicit val b: B = B()
+
+  def main(args: Array[String]) = {
+    println(foo[A, B])
+    println(foo[A, B](a))
+    println(foo(a)(b))
+    val s: implicit A => A = simple[A]
+    println(s)
+    val x0: implicit A => implicit B => (A, B) = foo[A, B]
+    println(x0)
+    val x1: implicit B => (A, B) = foo[A, B]
+    println(x1)
+
+    println(bar[A, B])
+    println(bar[A, B](a))
+    println(bar(a)(b))
+  }
+}