Allow class parents to be refined types.

Refinements of a class parent are added as synthetic members to the inheriting class.

Author: odersky

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

@@ -5,6 +5,7 @@ package core
 import Contexts.*, Symbols.*, Types.*, Flags.*, Scopes.*, Decorators.*, Names.*, NameOps.*
 import SymDenotations.{LazyType, SymDenotation}, StdNames.nme
 import TypeApplications.EtaExpansion
+import collection.mutable
 
 /** Operations that are shared between Namer and TreeUnpickler */
 object NamerOps:
@@ -18,6 +19,26 @@ object NamerOps:
       case TypeSymbols(tparams) :: _ => ctor.owner.typeRef.appliedTo(tparams.map(_.typeRef))
       case _ => ctor.owner.typeRef
 
+  /** Split dependent class refinements off parent type. Add them to `refinements`,
+   *  unless it is null.
+   */
+  extension (tp: Type)
+    def separateRefinements(cls: ClassSymbol, refinements: mutable.LinkedHashMap[Name, Type] | Null)(using Context): Type =
+      tp match
+        case RefinedType(tp1, rname, rinfo) =>
+          try tp1.separateRefinements(cls, refinements)
+          finally
+            if refinements != null then
+              refinements(rname) = refinements.get(rname) match
+                case Some(tp) => tp & rinfo
+                case None => rinfo
+        case tp @ AnnotatedType(tp1, ann) =>
+          tp.derivedAnnotatedType(tp1.separateRefinements(cls, refinements), ann)
+        case tp: RecType =>
+          tp.parent.substRecThis(tp, cls.thisType).separateRefinements(cls, refinements)
+        case tp =>
+          tp
+
   /** If isConstructor, make sure it has at least one non-implicit parameter list
    *  This is done by adding a () in front of a leading old style implicit parameter,
    *  or by adding a () as last -- or only -- parameter list if the constructor has

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1043,7 +1043,7 @@ class TreeUnpickler(reader: TastyReader,
       }
       val parentReader = fork
       val parents = readParents(withArgs = false)(using parentCtx)
-      val parentTypes = parents.map(_.tpe.dealias)
+      val parentTypes = parents.map(_.tpe.dealiasKeepAnnots.separateRefinements(cls, null))
       val self =
         if (nextByte == SELFDEF) {
           readByte()

compiler/src/dotty/tools/dotc/transform/init/Util.scala

@@ -20,6 +20,7 @@ object Util:
 
   def typeRefOf(tp: Type)(using Context): TypeRef = tp.dealias.typeConstructor match
     case tref: TypeRef => tref
+    case RefinedType(parent, _, _) => typeRefOf(parent)
     case hklambda: HKTypeLambda => typeRefOf(hklambda.resType)
 
 

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

@@ -54,11 +54,12 @@ class Namer { typer: Typer =>
 
   import untpd.*
 
-  val TypedAhead      : Property.Key[tpd.Tree]            = new Property.Key
-  val ExpandedTree    : Property.Key[untpd.Tree]          = new Property.Key
-  val ExportForwarders: Property.Key[List[tpd.MemberDef]] = new Property.Key
-  val SymOfTree       : Property.Key[Symbol]              = new Property.Key
-  val AttachedDeriver : Property.Key[Deriver]             = new Property.Key
+  val TypedAhead       : Property.Key[tpd.Tree]            = new Property.Key
+  val ExpandedTree     : Property.Key[untpd.Tree]          = new Property.Key
+  val ExportForwarders : Property.Key[List[tpd.MemberDef]] = new Property.Key
+  val ParentRefinements: Property.Key[List[Symbol]]        = new Property.Key
+  val SymOfTree        : Property.Key[Symbol]              = new Property.Key
+  val AttachedDeriver  : Property.Key[Deriver]             = new Property.Key
     // was `val Deriver`, but that gave shadowing problems with constructor proxies
 
   /** A partial map from unexpanded member and pattern defs and to their expansions.
@@ -1485,6 +1486,7 @@ class Namer { typer: Typer =>
     /** The type signature of a ClassDef with given symbol */
     override def completeInCreationContext(denot: SymDenotation): Unit = {
       val parents = impl.parents
+      val parentRefinements = new mutable.LinkedHashMap[Name, Type]
 
       /* The type of a parent constructor. Types constructor arguments
        * only if parent type contains uninstantiated type parameters.
@@ -1536,7 +1538,8 @@ class Namer { typer: Typer =>
         val ptype = parentType(parent)(using completerCtx.superCallContext).dealiasKeepAnnots
         if (cls.isRefinementClass) ptype
         else {
-          val pt = checkClassType(ptype, parent.srcPos,
+          val pt = checkClassType(
+              ptype.separateRefinements(cls, parentRefinements), parent.srcPos,
               traitReq = parent ne parents.head, stablePrefixReq = true)
           if (pt.derivesFrom(cls)) {
             val addendum = parent match {
@@ -1564,6 +1567,21 @@ class Namer { typer: Typer =>
         }
       }
 
+      /** Enter all parent refinements as public class members, unless a definition
+       *  with the same name already exists in the class.
+       */
+      def enterParentRefinementSyms(refinements: List[(Name, Type)]) =
+        val refinedSyms = mutable.ListBuffer[Symbol]()
+        for (name, tp) <- refinements do
+          if decls.lookupEntry(name) == null then
+            val flags = tp match
+              case tp: MethodOrPoly => Method | Synthetic | Deferred
+              case _ => Synthetic | Deferred
+            refinedSyms += newSymbol(cls, name, flags, tp, coord = original.rhs.span.startPos).entered
+        if refinedSyms.nonEmpty then
+          typr.println(i"parent refinement symbols: ${refinedSyms.toList}")
+          original.pushAttachment(ParentRefinements, refinedSyms.toList)
+
       /** If `parents` contains references to traits that have supertraits with implicit parameters
        *  add those supertraits in linearization order unless they are already covered by other
        *  parent types. For instance, in
@@ -1632,6 +1650,7 @@ class Namer { typer: Typer =>
       cls.invalidateMemberCaches() // we might have checked for a member when parents were not known yet.
       cls.setNoInitsFlags(parentsKind(parents), untpd.bodyKind(rest))
       cls.setStableConstructor()
+      enterParentRefinementSyms(parentRefinements.toList)
       processExports(using localCtx)
       defn.patchStdLibClass(cls)
       addConstructorProxies(cls)

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

@@ -911,7 +911,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         if (templ1.parents.isEmpty &&
             isFullyDefined(pt, ForceDegree.flipBottom) &&
             isSkolemFree(pt) &&
-            isEligible(pt.underlyingClassRef(refinementOK = false)))
+            isEligible(pt.underlyingClassRef(refinementOK = true)))
           templ1 = cpy.Template(templ)(parents = untpd.TypeTree(pt) :: Nil)
         for case parent: RefTree <- templ1.parents do
           typedAhead(parent, tree => inferTypeParams(typedType(tree), pt))
@@ -2759,6 +2759,19 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       }
     }
 
+    /** Add all parent refinement symbols as declarations to this class */
+    def addParentRefinements(body: List[Tree])(using Context): List[Tree] =
+      cdef.getAttachment(ParentRefinements) match
+        case Some(refinedSyms) =>
+          val refinements = refinedSyms.map: sym =>
+            ( if sym.isType then TypeDef(sym.asType)
+              else if sym.is(Method) then DefDef(sym.asTerm)
+              else ValDef(sym.asTerm)
+            ).withSpan(impl.span.startPos)
+          body ++ refinements
+        case None =>
+          body
+
     ensureCorrectSuperClass()
     completeAnnotations(cdef, cls)
     val constr1 = typed(constr).asInstanceOf[DefDef]
@@ -2779,7 +2792,10 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       cdef.withType(UnspecifiedErrorType)
     else {
       val dummy = localDummy(cls, impl)
-      val body1 = addAccessorDefs(cls, typedStats(impl.body, dummy)(using ctx.inClassContext(self1.symbol))._1)
+      val body1 =
+        addParentRefinements(
+          addAccessorDefs(cls,
+            typedStats(impl.body, dummy)(using ctx.inClassContext(self1.symbol))._1))
 
       checkNoDoubleDeclaration(cls)
       val impl1 = cpy.Template(impl)(constr1, parents1, Nil, self1, body1)

tests/neg/i0248-inherit-refined.scala

@@ -1,10 +1,10 @@
 object test {
   class A { type T }
   type X = A { type T = Int }
-  class B extends X                                   // error
+  class B extends X                                   // was error, now OK
   type Y = A & B
   class C extends Y                                   // error
   type Z = A | B
   class D extends Z                                   // error
-  abstract class E extends ({ val x: Int })           // error
+  abstract class E extends ({ val x: Int })           // was error, now OK
 }

tests/neg/parent-refinement-access.check

@@ -0,0 +1,7 @@
+-- [E164] Declaration Error: tests/neg/parent-refinement-access.scala:4:6 ----------------------------------------------
+4 |trait Year2(private[Year2] val value: Int) extends (Gen { val x: Int }) // error
+  |      ^
+  |      error overriding value x in trait Year2 of type Int;
+  |        value x in trait Gen of type Any has weaker access privileges; it should be public
+  |      (Note that value x in trait Year2 of type Int is abstract,
+  |      and is therefore overridden by concrete value x in trait Gen of type Any)

tests/neg/parent-refinement-access.scala

@@ -0,0 +1,4 @@
+trait Gen:
+  private[Gen] val x: Any = ()
+
+trait Year2(private[Year2] val value: Int) extends (Gen { val x: Int }) // error

tests/neg/parent-refinement.check

@@ -1,4 +1,25 @@
--- Error: tests/neg/parent-refinement.scala:5:2 ------------------------------------------------------------------------
-5 |  with Ordered[Year] { // error
-  |  ^^^^
-  |  end of toplevel definition expected but 'with' found
+-- Error: tests/neg/parent-refinement.scala:10:6 -----------------------------------------------------------------------
+10 |class Bar extends IdOf[Int], (X { type Value = String }) // error
+   |      ^^^
+   |class Bar cannot be instantiated since it has a member Value with possibly conflicting bounds Int | String <: ... <: Int & String
+-- [E007] Type Mismatch Error: tests/neg/parent-refinement.scala:14:17 -------------------------------------------------
+14 |  val x: Value = 0 // error
+   |                 ^
+   |                 Found:    (0 : Int)
+   |                 Required: Baz.this.Value
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/parent-refinement.scala:20:6 --------------------------------------------------
+20 |  foo(2) // error
+   |      ^
+   |      Found:    (2 : Int)
+   |      Required: Boolean
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/parent-refinement.scala:16:22 -------------------------------------------------
+16 |val x: IdOf[Int] = Baz() // error
+   |                   ^^^^^
+   |                   Found:    Baz
+   |                   Required: IdOf[Int]
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/parent-refinement.scala

@@ -1,7 +1,20 @@
 
 trait Id { type Value }
+trait X { type Value }
+type IdOf[T] = Id { type Value = T }
+
 case class Year(value: Int) extends AnyVal
-  with Id { type Value = Int }
-  with Ordered[Year] { // error
+  with (Id { type Value = Int })
+  with Ordered[Year]
+
+class Bar extends IdOf[Int], (X { type Value = String }) // error
+
+class Baz extends IdOf[Int]:
+  type Value = String
+  val x: Value = 0 // error
+
+val x: IdOf[Int] = Baz() // error
 
-}
+object Clash extends ({ def foo(x: Int): Int }):
+  def foo(x: Boolean): Int = 1
+  foo(2) // error