Fix #2677: Several fixes involving super selection

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

@@ -1407,32 +1407,13 @@ object SymDenotations {
       baseData._2
 
     def computeBaseData(implicit onBehalf: BaseData, ctx: Context): (List[ClassSymbol], BaseClassSet) = {
-      val seen = new BaseClassSetBuilder
-      def addBaseClasses(bcs: List[ClassSymbol], to: List[ClassSymbol])
-          : List[ClassSymbol] = bcs match {
-        case bc :: bcs1 =>
-          val bcs1added = addBaseClasses(bcs1, to)
-          if (seen contains bc) bcs1added
-          else {
-            seen.add(bc)
-            bc :: bcs1added
-          }
-        case nil =>
-          to
-      }
-      def addParentBaseClasses(ps: List[TypeRef], to: List[ClassSymbol]): List[ClassSymbol] = ps match {
-        case p :: ps1 =>
-          addParentBaseClasses(ps1,
-              addBaseClasses(p.symbol.asClass.baseClasses, to))
-        case nil =>
-          to
-      }
       def emptyParentsExpected =
         is(Package) || (symbol == defn.AnyClass) || ctx.erasedTypes && (symbol == defn.ObjectClass)
       if (classParents.isEmpty && !emptyParentsExpected)
         onBehalf.signalProvisional()
-      (classSymbol :: addParentBaseClasses(classParents, Nil),
-       seen.result)
+      val builder = new BaseDataBuilder
+      for (p <- classParents) builder.addAll(p.symbol.asClass.baseClasses)
+      (classSymbol :: builder.baseClasses, builder.baseClassSet)
     }
 
     final override def derivesFrom(base: Symbol)(implicit ctx: Context): Boolean =
@@ -2096,7 +2077,14 @@ object SymDenotations {
     def contains(sym: Symbol): Boolean = contains(sym, classIds.length)
   }
 
-  private class BaseClassSetBuilder {
+  object BaseClassSet {
+    def apply(bcs: List[ClassSymbol]): BaseClassSet =
+      new BaseClassSet(bcs.toArray.map(_.id))
+  }
+
+  /** A class to combine base data from parent types */
+  class BaseDataBuilder {
+    private var classes: List[ClassSymbol] = Nil
     private var classIds = new Array[Int](32)
     private var length = 0
 
@@ -2106,19 +2094,32 @@ object SymDenotations {
       classIds = classIds1
     }
 
-    def contains(sym: Symbol): Boolean =
-      new BaseClassSet(classIds).contains(sym, length)
-
-    def add(sym: Symbol): Unit = {
+    private def add(sym: Symbol): Unit = {
       if (length == classIds.length) resize(length * 2)
       classIds(length) = sym.id
       length += 1
     }
 
-    def result = {
+    def addAll(bcs: List[ClassSymbol]): this.type = {
+      val len = length
+      bcs match {
+        case bc :: bcs1 =>
+          addAll(bcs1)
+          if (!new BaseClassSet(classIds).contains(bc, len)) {
+            add(bc)
+            classes = bc :: classes
+          }
+        case nil =>
+      }
+      this
+    }
+
+    def baseClassSet = {
       if (length != classIds.length) resize(length)
       new BaseClassSet(classIds)
     }
+
+    def baseClasses: List[ClassSymbol] = classes
   }
 
   @sharable private var indent = 0 // for completions printing

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

@@ -1143,11 +1143,11 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           case OrType(tp11, tp12) =>
             tp11 & tp2 | tp12 & tp2
           case _ =>
-            val t1 = mergeIfSub(tp1, tp2)
-            if (t1.exists) t1
+            val tp1a = dropIfSuper(tp1, tp2)
+            if (tp1a ne tp1) glb(tp1a, tp2)
             else {
-              val t2 = mergeIfSub(tp2, tp1)
-              if (t2.exists) t2
+              val tp2a = dropIfSuper(tp2, tp1)
+              if (tp2a ne tp2) glb(tp1, tp2a)
               else tp1 match {
                 case tp1: ConstantType =>
                   tp2 match {
@@ -1204,6 +1204,22 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
   final def lub(tps: List[Type]): Type =
     ((defn.NothingType: Type) /: tps)(lub(_,_, canConstrain = false))
 
+  private def recombineAndOr(tp: AndOrType, tp1: Type, tp2: Type) =
+    if (!tp1.exists) tp2
+    else if (!tp2.exists) tp1
+    else tp.derivedAndOrType(tp1, tp2)
+
+  /** If some (&-operand of) this type is a supertype of `sub` replace it with `NoType`.
+   */
+  private def dropIfSuper(tp: Type, sub: Type): Type =
+    if (isSubTypeWhenFrozen(sub, tp)) NoType
+    else tp match {
+      case tp @ AndType(tp1, tp2) =>
+        recombineAndOr(tp, dropIfSuper(tp1, sub), dropIfSuper(tp2, sub))
+      case _ =>
+        tp
+    }
+
   /** Merge `t1` into `tp2` if t1 is a subtype of some &-summand of tp2.
    */
   private def mergeIfSub(tp1: Type, tp2: Type): Type =

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

@@ -384,19 +384,15 @@ object Types {
 
     /** The base classes of this type as determined by ClassDenotation
      *  in linearization order, with the class itself as first element.
-     *  For AndTypes/OrTypes, the union/intersection of the operands' baseclasses.
-     *  Inherited by all type proxies. `Nil` for all other types.
+     *  Inherited by all type proxies. Overridden for And and Or types.
+     *  `Nil` for all other types.
      */
-    final def baseClasses(implicit ctx: Context): List[ClassSymbol] = track("baseClasses") {
+    def baseClasses(implicit ctx: Context): List[ClassSymbol] = track("baseClasses") {
       this match {
         case tp: TypeProxy =>
           tp.underlying.baseClasses
         case tp: ClassInfo =>
           tp.cls.baseClasses
-        case AndType(tp1, tp2) =>
-          tp1.baseClasses union tp2.baseClasses
-        case OrType(tp1, tp2) =>
-          tp1.baseClasses intersect tp2.baseClasses
         case _ => Nil
       }
     }
@@ -472,22 +468,24 @@ object Types {
      */
     final def findMember(name: Name, pre: Type, excluded: FlagSet)(implicit ctx: Context): Denotation = {
       @tailrec def go(tp: Type): Denotation = tp match {
-        case tp: RefinedType =>
-          if (name eq tp.refinedName) goRefined(tp) else go(tp.parent)
-        case tp: ThisType =>
-          goThis(tp)
-        case tp: TypeRef =>
-          tp.denot.findMember(name, pre, excluded)
         case tp: TermRef =>
           go (tp.underlying match {
             case mt: MethodType
             if mt.paramInfos.isEmpty && (tp.symbol is Stable) => mt.resultType
             case tp1 => tp1
           })
-        case tp: TypeParamRef =>
-          goParam(tp)
+        case tp: TypeRef =>
+          tp.denot.findMember(name, pre, excluded)
+        case tp: ThisType =>
+          goThis(tp)
+        case tp: RefinedType =>
+          if (name eq tp.refinedName) goRefined(tp) else go(tp.parent)
         case tp: RecType =>
           goRec(tp)
+        case tp: TypeParamRef =>
+          goParam(tp)
+        case tp: SuperType =>
+          goSuper(tp)
         case tp: HKApply =>
           goApply(tp)
         case tp: TypeProxy =>
@@ -611,6 +609,12 @@ object Types {
             go(next)
         }
       }
+      def goSuper(tp: SuperType) = go(tp.underlying) match {
+        case d: JointRefDenotation =>
+          typr.println(i"redirecting super.$name from $tp to ${d.symbol.showLocated}")
+          new UniqueRefDenotation(d.symbol, tp.memberInfo(d.symbol), d.validFor)
+        case d => d
+      }
       def goAnd(l: Type, r: Type) = {
         go(l) & (go(r), pre, safeIntersection = ctx.pendingMemberSearches.contains(name))
       }
@@ -2296,6 +2300,37 @@ object Types {
     def tp2: Type
     def isAnd: Boolean
     def derivedAndOrType(tp1: Type, tp2: Type)(implicit ctx: Context): Type  // needed?
+
+    private[this] var myBaseClassesPeriod: Period = Nowhere
+    private[this] var myBaseClasses: List[ClassSymbol] = _
+
+    /** Base classes of And are the merge of the operand base classes
+     *  For OrTypes, it's the intersection.
+     */
+    override final def baseClasses(implicit ctx: Context) = {
+      if (myBaseClassesPeriod != ctx.period) {
+        val bcs1 = tp1.baseClasses
+        val bcs1set = BaseClassSet(bcs1)
+        def recur(bcs2: List[ClassSymbol]): List[ClassSymbol] = bcs2 match {
+          case bc2 :: bcs2rest =>
+            if (isAnd)
+              if (bcs1set contains bc2)
+                if (bc2.is(Trait)) recur(bcs2rest)
+                else bcs1 // common class, therefore rest is the same in both sequences
+              else bc2 :: recur(bcs2rest)
+            else
+              if (bcs1set contains bc2)
+                if (bc2.is(Trait)) bc2 :: recur(bcs2rest)
+                else bcs2
+              else recur(bcs2rest)
+          case nil =>
+            if (isAnd) bcs1 else bcs2
+        }
+        myBaseClasses = recur(tp2.baseClasses)
+        myBaseClassesPeriod = ctx.period
+      }
+      myBaseClasses
+    }
   }
 
   abstract case class AndType(tp1: Type, tp2: Type) extends CachedGroundType with AndOrType {

tests/neg/i2677.scala

@@ -0,0 +1,6 @@
+trait A { def x = "foo" }
+trait B { def x = 42 }
+object Test {
+  val AB = new A with B { override def x = super.x } // error: wrong override
+  AB.x
+}

tests/neg/overrides.scala

@@ -79,27 +79,6 @@ class X3 {
   override type T = A1 // error: overrides nothing
 }
 
-package p3 {
-
-// Dotty change of rules: Toverrider#f does not
-// override TCommon#f, hence the accidental override rule
-// applies.
-trait TCommon {
-  def f: String
-}
-
-class C1 extends TCommon {
-  def f = "in C1"
-}
-
-trait TOverrider { this: TCommon =>
-  override def f = "in TOverrider"   // The overridden self-type member...
-}
-
-class C2 extends C1 with TOverrider  // ... fails to override, here. // error: accidental override
-
-}
-
 package p4 {
 
   abstract class C[T] { def head: T }

tests/pos/Orderings.scala

@@ -0,0 +1,20 @@
+object Orderings {
+
+  // A type class:
+  trait Ord[T] { def less(x: T, y: T): Boolean }
+
+  implicit val intOrd: Ord[Int] = new {
+    def less(x: Int, y: Int) = x < y
+  }
+
+  implicit def listOrd[T](implicit ev: Ord[T]): Ord[List[T]] = new {
+    def less(xs: List[T], ys: List[T]): Boolean =
+      if ys.isEmpty then false
+      else if xs.isEmpty then true
+      else if xs.head == ys.head then less(xs.tail, ys.tail)
+      else ev.less(xs.head, ys.head)
+  }
+
+  def isLess[T]: T => T => implicit Ord[T] => Boolean =
+    x => y => implicitly[Ord[T]].less(x, y)
+}

tests/pos/override-via-self.scala

@@ -0,0 +1,18 @@
+// Question: Does TOverrider#f override TCommon#f?
+// If not, the accidental override rule applies.
+// Dotty used to say no, but with the change to baseClasses in AndTypes says
+// yes. Not sure what the right answer is. But in any case we should
+// keep the test to notice if there's a difference in behavior.
+trait TCommon {
+  def f: String
+}
+class C1 extends TCommon {
+  def f = "in C1"
+}
+
+trait TOverrider { this: TCommon =>
+  override def f = "in TOverrider"   // The overridden self-type member...
+}
+
+class C2 extends C1 with TOverrider  // ... failed to override, here. But now it is OK.
+

tests/run/supercalls-traits.check

@@ -0,0 +1,5 @@
+C1A1A2B1B2C2
+C1B3B4C3
+IT
+AT
+ER

tests/run/supercalls-traits.scala

@@ -14,9 +14,42 @@ class Base[A](exp: => Option[A])
 
 object Empty extends Base[Nothing](None)
 
+
+trait B1 extends C1 { override def f() = { super.f(); print("B1") }}
+trait B2 extends B1 { override def f() = { super.f(); print("B2") }}
+trait A1 extends C1 { override def f() = { super.f(); print("A1") }}
+trait A2 extends A1 { override def f() = { super.f(); print("A2") }}
+class C1 { def f() = print("C1") }
+class C2 extends A2 with B2 { override def f() = { super.f(); print("C2") }}
+
+
+trait B3 extends C1 { override def f() = { super.f(); print("B3") }}
+trait B4 extends C1 { this: B3 =>  override def f() = { super.f(); print("B4") }}
+class C3 extends C1 with B3 with B4 { override def f() = { super.f(); print("C3") }}
+
+trait DT {
+  def f(): Unit
+}
+trait IT extends DT {
+  def f() = { println("IT") }
+}
+abstract class MPT {
+}
+trait AT extends MPT with DT {
+  abstract override def f() = { super.f(); println("AT") }
+}
+class ER extends MPT with IT with AT {
+  override def f() = { super.f(); println("ER") }
+}
+
 object Test {
   def main(args: Array[String]): Unit = {
     assert(new C().foo == 3)
+    new C2().f()
+    println()
+    new C3().f()
+    println()
+    new ER().f()
     Empty
   }
 }