Make scheme work also for nested classes and companion objects

Author: odersky

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -400,6 +400,26 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     case ConstantType(value) => Literal(value)
   }
 
+  /** A path that corresponds to the given type `tp`. Error if `tp` is not a refinement
+   *  of an addressable singleton type.
+   */
+  def pathFor(tp: Type)(implicit ctx: Context): Tree = {
+    def recur(tp: Type): Tree = tp match {
+      case tp: NamedType =>
+        tp.info match {
+          case TypeAlias(alias) => recur(alias)
+          case _: TypeBounds => EmptyTree
+          case _ => singleton(tp)
+        }
+      case tp: TypeProxy => recur(tp.superType)
+      case _ => EmptyTree
+    }
+    recur(tp).orElse {
+      ctx.error(em"$tp is not an addressable singleton type")
+      TypeTree(tp)
+    }
+  }
+
   /** A tree representing a `newXYZArray` operation of the right
    *  kind for the given element type in `elemTpe`. No type arguments or
    *  `length` arguments are given.

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

@@ -66,5 +66,15 @@ object TypeUtils {
     }
 
     def refinedWith(name: Name, info: Type)(implicit ctx: Context) = RefinedType(self, name, info)
+
+    /** The TermRef referring to the companion of the underlying class reference
+     *  of this type, while keeping the same prefix.
+     */
+    def companionRef(implicit ctx: Context): TermRef = self match {
+      case self @ TypeRef(prefix, _) if self.symbol.isClass =>
+        prefix.select(self.symbol.companionModule).asInstanceOf[TermRef]
+      case self: TypeProxy =>
+        self.underlying.companionRef
+    }
   }
 }

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

@@ -868,6 +868,13 @@ trait Implicits { self: Typer =>
       .refinedWith(tpnme.MirroredMonoType, TypeAlias(monoType))
       .refinedWith(tpnme.MirroredLabel, TypeAlias(ConstantType(Constant(label.toString))))
 
+  /** A path referencing the companion of class type `clsType` */
+  private def companionPath(clsType: Type, span: Span)(implicit ctx: Context) = {
+    val ref = pathFor(clsType.companionRef)
+    assert(ref.symbol.is(Module) && ref.symbol.companionClass == clsType.classSymbol)
+    ref.withSpan(span)
+  }
+
   /** An implied instance for a type of the form `Mirror.Product { type MirroredMonoType = T }`
    *  where `T` is a generic product type or a case object or an enum case.
    */
@@ -878,16 +885,16 @@ trait Implicits { self: Typer =>
           mirrorFor(tp1).orElse(mirrorFor(tp2))
         case _ =>
           if (monoType.termSymbol.is(CaseVal)) {
-            val modul = monoType.termSymbol
-            if (modul.info.classSymbol.is(Scala2x)) {
-              val mirrorType = mirrorCore(defn.Mirror_SingletonProxyType, monoType, modul.name)
-              val mirrorRef = New(defn.Mirror_SingletonProxyType, ref(modul).withSpan(span) :: Nil)
+            val module = monoType.termSymbol
+            val modulePath = pathFor(monoType).withSpan(span)
+            if (module.info.classSymbol.is(Scala2x)) {
+              val mirrorType = mirrorCore(defn.Mirror_SingletonProxyType, monoType, module.name)
+              val mirrorRef = New(defn.Mirror_SingletonProxyType, modulePath :: Nil)
               mirrorRef.cast(mirrorType)
             }
             else {
-              val mirrorType = mirrorCore(defn.Mirror_SingletonType, monoType, modul.name)
-              val mirrorRef = ref(modul).withSpan(span)
-              mirrorRef.cast(mirrorType)
+              val mirrorType = mirrorCore(defn.Mirror_SingletonType, monoType, module.name)
+              modulePath.cast(mirrorType)
             }
           }
           else if (monoType.classSymbol.isGenericProduct) {
@@ -899,11 +906,9 @@ trait Implicits { self: Typer =>
               mirrorCore(defn.Mirror_ProductType, monoType, cls.name)
                 .refinedWith(tpnme.MirroredElemTypes, TypeAlias(TypeOps.nestedPairs(elemTypes)))
                 .refinedWith(tpnme.MirroredElemLabels, TypeAlias(TypeOps.nestedPairs(elemLabels)))
-            val modul = cls.linkedClass.sourceModule
-            assert(modul.is(Module))
             val mirrorRef =
               if (cls.is(Scala2x)) anonymousMirror(monoType, ExtendsProductMirror, span)
-              else ref(modul).withSpan(span)
+              else companionPath(monoType, span)
             mirrorRef.cast(mirrorType)
           }
           else EmptyTree
@@ -955,9 +960,8 @@ trait Implicits { self: Typer =>
           val mirrorType =
              mirrorCore(defn.Mirror_SumType, monoType, cls.name)
               .refinedWith(tpnme.MirroredElemTypes, TypeAlias(TypeOps.nestedPairs(elemTypes)))
-          val modul = cls.linkedClass.sourceModule
           val mirrorRef =
-            if (modul.exists && !cls.is(Scala2x)) ref(modul).withSpan(span)
+            if (cls.linkedClass.exists && !cls.is(Scala2x)) companionPath(monoType, span)
             else anonymousMirror(monoType, ExtendsSumMirror, span)
           mirrorRef.cast(mirrorType)
         case _ =>