Merge pull request #7560 from dotty-staging/fix-#7526

Fix #7526: Don't check class info within bounds when taking denotions

Author: odersky

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

@@ -459,7 +459,7 @@ object Denotations {
         /** Sym preference provided types also override */
         def prefer(sym1: Symbol, sym2: Symbol, info1: Type, info2: Type) =
           preferSym(sym1, sym2) &&
-          info1.overrides(info2, sym1.matchNullaryLoosely || sym2.matchNullaryLoosely)
+          info1.overrides(info2, sym1.matchNullaryLoosely || sym2.matchNullaryLoosely, checkClassInfo = false)
 
         def handleDoubleDef =
           if (preferSym(sym1, sym2)) denot1
@@ -600,13 +600,13 @@ object Denotations {
       case tp1: TypeBounds =>
         tp2 match {
           case tp2: TypeBounds => if (safeIntersection) tp1 safe_& tp2 else tp1 & tp2
-          case tp2: ClassInfo if tp1 contains tp2 => tp2
+          case tp2: ClassInfo => tp2
           case _ => mergeConflict(sym1, sym2, tp1, tp2)
         }
       case tp1: ClassInfo =>
         tp2 match {
           case tp2: ClassInfo if tp1.cls eq tp2.cls => tp1.derivedClassInfo(tp1.prefix & tp2.prefix)
-          case tp2: TypeBounds if tp2 contains tp1 => tp1
+          case tp2: TypeBounds => tp1
           case _ => mergeConflict(sym1, sym2, tp1, tp2)
         }
 

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

@@ -911,21 +911,21 @@ object Types {
 
     /** Is this type a legal type for member `sym1` that overrides another
      *  member `sym2` of type `that`? This is the same as `<:<`, except that
-     *  if `matchLoosely` evaluates to true the types `=> T` and `()T` are seen
-     *  as overriding each other.
+     *  @param matchLoosely   if true the types `=> T` and `()T` are seen as overriding each other.
+     *  @param checkClassInfo if true we check that ClassInfos are within bounds of abstract types
      */
-    final def overrides(that: Type, matchLoosely: => Boolean)(implicit ctx: Context): Boolean = {
+    final def overrides(that: Type, matchLoosely: => Boolean, checkClassInfo: Boolean = true)(implicit ctx: Context): Boolean = {
       def widenNullary(tp: Type) = tp match {
         case tp @ MethodType(Nil) => tp.resultType
         case _ => tp
       }
-      ((this.widenExpr frozen_<:< that.widenExpr) ||
-        matchLoosely && {
-          val this1 = widenNullary(this)
-          val that1 = widenNullary(that)
-          ((this1 `ne` this) || (that1 `ne` that)) && this1.overrides(that1, matchLoosely = false)
-        }
-      )
+      !checkClassInfo && this.isInstanceOf[ClassInfo]
+      || (this.widenExpr frozen_<:< that.widenExpr)
+      || matchLoosely && {
+           val this1 = widenNullary(this)
+           val that1 = widenNullary(that)
+           ((this1 `ne` this) || (that1 `ne` that)) && this1.overrides(that1, false, checkClassInfo)
+         }
     }
 
     /** Is this type close enough to that type so that members

tests/neg/i7526.scala

@@ -0,0 +1,18 @@
+type Tr[-I, +O, +A] = I => (O, A)
+
+trait NetApi with
+  type Comp
+
+trait NetDB extends NetApi with
+  class Comp
+
+trait NetHelper extends NetApi
+
+def compQ(name: => String)
+    : (given n: NetApi) => Tr[Nothing, n.Comp, n.Comp] = ???
+
+object net extends NetDB with NetHelper
+import net._
+given n: NetApi = net
+
+val q: Tr[Nothing, Comp, Comp] = compQ("???") // error Found: Tr[Nothing, ?1.Comp, ?1.Comp] Required: Tr[Nothing, net.Comp, net.Comp]

tests/neg/override-inner-class.scala

@@ -0,0 +1,5 @@
+class C
+  type T >: String <: Any
+
+class D extends C
+  class T  // error