A tweak of a tweak about owner scope disambiguation

Author: odersky

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

@@ -1963,8 +1963,11 @@ trait Applications extends Compatibility {
       else if winsPrefix1 then 1
       else -1
 
+    val ownerScore = compareOwner(alt1.symbol.maybeOwner, alt2.symbol.maybeOwner)
+    val implicitPair = alt1.symbol.is(Implicit) && alt2.symbol.is(Implicit)
+    val newGivenRules = preferGeneral && !ctx.mode.is(Mode.OldImplicitResolution)
+
     def compareWithTypes(tp1: Type, tp2: Type) =
-      val ownerScore = compareOwner(alt1.symbol.maybeOwner, alt2.symbol.maybeOwner)
       val winsType1 = isAsGood(alt1, tp1, alt2, tp2)
       val winsType2 = isAsGood(alt2, tp2, alt1, tp1)
 
@@ -1976,13 +1979,14 @@ trait Applications extends Compatibility {
         // (prefer the one that is not a method, but that's arbitrary).
         if alt1.widenExpr =:= alt2 then -1 else 1
       else
-        // For implicit resolution, take ownerscore as more significant than type resolution
+        // For new implicit resolution, take ownerscore as more significant than type resolution
         // Reason: People use owner hierarchies to explicitly prioritize, we should not
         // break that by changing implicit priority of types.
+        // But don't do that for implicit/implicit pairs. It's better to leave
+        // them ambiguous so that the logic in Implicits/compareAlternatives kicks in
+        // which resolves them with the old rules.
         def drawOrOwner =
-          if preferGeneral && !ctx.mode.is(Mode.OldImplicitResolution)
-          then ownerScore
-          else 0
+          if newGivenRules && !implicitPair then ownerScore else 0
         ownerScore match
           case  1 => if winsType1 || !winsType2 then  1 else drawOrOwner
           case -1 => if winsType2 || !winsType1 then -1 else drawOrOwner
@@ -2002,6 +2006,13 @@ trait Applications extends Compatibility {
 
       var result = compareWithTypes(strippedType1, strippedType2)
       if result != 0 then result
+      else if ownerScore != 0 && newGivenRules && implicitPair then
+        0                                         // for implicit/implicit pairs fail fast
+                                                  // so that we retry in compareAlternatives with old rules.
+                                                  // Note: This is problematic since it fails the transitity
+                                                  // requirement, i.e compareAlternatives is not a partial order
+                                                  // anymore. But it might be needed to keep the number of failing
+                                                  // projects smaller
       else if strippedType1 eq fullType1 then
         if strippedType2 eq fullType2 then 0      // no implicits either side: its' a draw
         else 1                                    // prefer 1st alternative with no implicits

tests/neg/scala-uri.check

@@ -6,9 +6,9 @@
    |
    |    QueryKeyValue.tuple2QueryKeyValue[String, None.type](QueryKey.stringQueryKey,
    |      QueryValue.optionQueryValue[A](
-   |        /* ambiguous: both value stringQueryValue in trait QueryValueInstances1 and value noneQueryValue in trait QueryValueInstances1 match type QueryValue[A] */
+   |        /* ambiguous: both given instance stringQueryValue in trait QueryValueInstances1 and given instance noneQueryValue in trait QueryValueInstances1 match type QueryValue[A] */
    |          summon[QueryValue[A]]
    |      )
    |    )
    |
-   |But both value stringQueryValue in trait QueryValueInstances1 and value noneQueryValue in trait QueryValueInstances1 match type QueryValue[A].
+   |But both given instance stringQueryValue in trait QueryValueInstances1 and given instance noneQueryValue in trait QueryValueInstances1 match type QueryValue[A].

tests/neg/scala-uri.scala

@@ -3,13 +3,13 @@ import scala.language.implicitConversions
 trait QueryKey[A]
 object QueryKey extends QueryKeyInstances
 sealed trait QueryKeyInstances:
-  implicit val stringQueryKey: QueryKey[String] = ???
+  given stringQueryKey: QueryKey[String] = ???
 
 trait QueryValue[-A]
 object QueryValue extends QueryValueInstances
 sealed trait QueryValueInstances1:
-  implicit final val stringQueryValue: QueryValue[String] = ???
-  implicit final val noneQueryValue: QueryValue[None.type] = ???
+  given stringQueryValue: QueryValue[String] = ???
+  given noneQueryValue: QueryValue[None.type] = ???
     // The noneQueryValue makes no sense at this priority. Since QueryValue
     // is contravariant, QueryValue[None.type] is always better than QueryValue[Option[A]]
     // no matter whether it's old or new resolution. So taking both owner and type
@@ -20,11 +20,11 @@ sealed trait QueryValueInstances1:
     // same trait as QueryValue[Option[A]], as is shown in pos/scala-uri.scala.
 
 sealed trait QueryValueInstances extends QueryValueInstances1:
-  implicit final def optionQueryValue[A: QueryValue]: QueryValue[Option[A]] = ???
+  given optionQueryValue[A: QueryValue]: QueryValue[Option[A]] = ???
 
 trait QueryKeyValue[A]
 object QueryKeyValue:
-  implicit def tuple2QueryKeyValue[K: QueryKey, V: QueryValue]: QueryKeyValue[(K, V)] = ???
+  given tuple2QueryKeyValue[K: QueryKey, V: QueryValue]: QueryKeyValue[(K, V)] = ???
 
 
 @main def Test = summon[QueryKeyValue[(String, None.type)]]  // error

tests/pos/i21320.scala

@@ -0,0 +1,73 @@
+import scala.deriving.*
+import scala.compiletime.*
+
+trait ConfigMonoid[T]:
+  def zero: T
+  def orElse(main: T, defaults: T): T
+
+object ConfigMonoid:
+  given option[T]: ConfigMonoid[Option[T]] = ???
+
+  inline def zeroTuple[C <: Tuple]: Tuple =
+    inline erasedValue[C] match
+      case _: EmptyTuple => EmptyTuple
+      case _: (t *: ts) =>
+        summonInline[ConfigMonoid[t]].zero *: zeroTuple[ts]
+
+  inline def valueTuple[C <: Tuple, T](index: Int, main: T, defaults: T): Tuple =
+    inline erasedValue[C] match
+      case _: EmptyTuple => EmptyTuple
+      case _: (t *: ts) =>
+        def get(v: T) = v.asInstanceOf[Product].productElement(index).asInstanceOf[t]
+        summonInline[ConfigMonoid[t]].orElse(get(main), get(defaults)) *: valueTuple[ts, T](
+          index + 1,
+          main,
+          defaults
+        )
+
+  inline given derive[T](using m: Mirror.ProductOf[T]): ConfigMonoid[T] =
+    new ConfigMonoid[T]:
+      def zero: T = m.fromProduct(zeroTuple[m.MirroredElemTypes])
+      def orElse(main: T, defaults: T): T = m.fromProduct(valueTuple[m.MirroredElemTypes, T](0, main, defaults))
+
+
+
+final case class PublishOptions(
+  v1: Option[String] = None,
+  v2: Option[String] = None,
+  v3: Option[String] = None,
+  v4: Option[String] = None,
+  v5: Option[String] = None,
+  v6: Option[String] = None,
+  v7: Option[String] = None,
+  v8: Option[String] = None,
+  v9: Option[String] = None,
+  ci: PublishContextualOptions = PublishContextualOptions(),
+)
+object PublishOptions:
+  implicit val monoid: ConfigMonoid[PublishOptions] = ConfigMonoid.derive
+
+final case class PublishContextualOptions(
+  v1: Option[String] = None,
+  v2: Option[String] = None,
+  v3: Option[String] = None,
+  v4: Option[String] = None,
+  v5: Option[String] = None,
+  v6: Option[String] = None,
+  v7: Option[String] = None,
+  v8: Option[String] = None,
+  v9: Option[String] = None,
+  v10: Option[String] = None,
+  v11: Option[String] = None,
+  v12: Option[String] = None,
+  v13: Option[String] = None,
+  v14: Option[String] = None,
+  v15: Option[String] = None,
+  v16: Option[String] = None,
+  v17: Option[String] = None,
+  v18: Option[String] = None,
+  v19: Option[String] = None,
+  v20: Option[String] = None
+)
+object PublishContextualOptions:
+  implicit val monoid: ConfigMonoid[PublishContextualOptions] = ConfigMonoid.derive

tests/pos/scala-uri.scala

@@ -1,3 +1,4 @@
+// This works for implicit/implicit pairs but not for givens, see neg version.
 import scala.language.implicitConversions
 
 trait QueryKey[A]
@@ -9,14 +10,13 @@ trait QueryValue[-A]
 object QueryValue extends QueryValueInstances
 sealed trait QueryValueInstances1:
   implicit final val stringQueryValue: QueryValue[String] = ???
+  implicit final val noneQueryValue: QueryValue[None.type] = ???
 
 sealed trait QueryValueInstances extends QueryValueInstances1:
   implicit final def optionQueryValue[A: QueryValue]: QueryValue[Option[A]] = ???
-  implicit final val noneQueryValue: QueryValue[None.type] = ???
 
 trait QueryKeyValue[A]
 object QueryKeyValue:
   implicit def tuple2QueryKeyValue[K: QueryKey, V: QueryValue]: QueryKeyValue[(K, V)] = ???
 
-
 @main def Test = summon[QueryKeyValue[(String, None.type)]]