Revert "Compensate loss of transitivity" (#21356)

This reverts commit 7c4bd67
See [#21344 comment]
(#21344 (comment))

We will have to reconsider how to alleviate the transitory problem
before releasing 3.6.

Fixes #21320
Fixes #21352

Author: EugeneFlesselle

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

@@ -1385,6 +1385,8 @@ trait Implicits:
       def disambiguate(alt1: SearchResult, alt2: SearchSuccess) = alt1 match
         case alt1: SearchSuccess =>
           var diff = compareAlternatives(alt1, alt2, disambiguate = true)
+          assert(diff <= 0 || isWarnPriorityChangeVersion)
+            // diff > 0 candidates should already have been eliminated in `rank`
           if diff == 0 && alt1.ref =:= alt2.ref then
             diff = 1 // See i12951 for a test where this happens
           else if diff == 0 && alt2.isExtension then
@@ -1636,21 +1638,7 @@ trait Implicits:
             validateOrdering(ord)
             throw ex
 
-      val sorted = sort(eligible)
-      val res = sorted match
-        case first :: rest =>
-          val firstIsImplicit = first.ref.symbol.is(Implicit)
-          if rest.exists(_.ref.symbol.is(Implicit) != firstIsImplicit) then
-            // Mixture of implicits and givens
-            // Rank implicits first, then, if there is a given that it better than the best implicit(s)
-            // switch over to givens.
-            val (sortedImplicits, sortedGivens) = sorted.partition(_.ref.symbol.is(Implicit))
-            val implicitResult = rank(sortedImplicits, NoMatchingImplicitsFailure, Nil)
-            rank(sortedGivens, implicitResult, Nil)
-          else
-            rank(sorted, NoMatchingImplicitsFailure, Nil)
-        case _ =>
-          NoMatchingImplicitsFailure
+      val res = rank(sort(eligible), NoMatchingImplicitsFailure, Nil)
 
       // Issue all priority change warnings that can affect the result
       val shownWarnings = priorityChangeWarnings.toList.collect:

tests/pos/i21320.scala renamed to tests/pos/i21320a.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 // was crash

tests/pos/i21320b.scala

@@ -0,0 +1,19 @@
+//> using options -source:3.5
+
+case class Schema[T](format: String):
+  def asOption: Schema[Option[T]] = ???
+  def name(name: Option[SName]): Schema[T] = ???
+  def format(f: String): Schema[T] = ???
+
+object Schema extends SchemaCompanionMacros:
+  implicit def schemaForOption[T: Schema]: Schema[Option[T]] =
+    implicitly[Schema[T]]
+    ???
+
+trait SchemaCompanionMacros extends SchemaDerivation:
+  given derivedStringBasedUnionEnumeration[S](using IsUnionOf[String, S]): Schema[S] =
+    val x: Schema[S] = ???
+    x.name(None)
+
+@main def Test =
+  case class Foo(x: Int) derives Schema

tests/pos/i21352a/schema.scala

@@ -0,0 +1,26 @@
+//> using options -source:3.5
+
+import scala.deriving.*
+import scala.quoted.*
+
+trait SName
+abstract class CaseClass[Typeclass[_], Type]:
+  def param: CaseClass.Param[Typeclass, Type]
+
+object CaseClass:
+  trait Param[Typeclass[_], Type]:
+    type PType
+    def typeclass: Typeclass[PType]
+
+
+sealed trait IsUnionOf[T, A]
+object IsUnionOf:
+  transparent inline given derived[T, A]: IsUnionOf[T, A] = ${ deriveImpl[T, A] }
+  private def deriveImpl[T, A](using quotes: Quotes): Expr[IsUnionOf[T, A]] = ???
+
+trait SchemaDerivation:
+  inline implicit def derived[T](implicit m: Mirror.Of[T]): Schema[T] =
+    val ctx: CaseClass[Schema, T] = ???
+    val valueSchema = ctx.param.typeclass
+    val format = valueSchema.format
+    ???

tests/pos/i21352a/schemaDerivation.scala

@@ -0,0 +1,33 @@
+
+object serializer:
+  trait Reader[T]
+  trait Writer[T]
+  // Needs to be implicit val
+  implicit val UnitReader: Reader[Unit] = ???
+  implicit val StringReader: Reader[String] = ???
+  // A way to derive instances needs to be available
+  inline given superTypeReader[T: scala.reflect.ClassTag]: Reader[T] = ???
+import serializer.Reader
+
+trait Codec[T]
+trait Channel[F[_]]:
+  def notificationStub[In: Codec](): In => F[Unit]
+trait Monadic[F[_]]
+
+sealed abstract class LSPNotification():
+  type In
+  given inputReader: Reader[In]
+
+class PreparedNotification[X <: LSPNotification](val x: X, val in: x.In):
+  type In = x.In
+
+trait Communicate[F[_]]:
+  def notification[X <: LSPNotification](notif: X, in: notif.In): F[Unit]
+
+object Communicate:
+  given codec[T: Reader]: Codec[T] = ???
+
+  def channel[F[_]: Monadic](channel: Channel[F]) =
+    new Communicate[F]:
+      override def notification[X <: LSPNotification](notif: X, in: notif.In): F[Unit] =
+        channel.notificationStub().apply(in) // was error

tests/pos/i21352b.scala

@@ -0,0 +1,17 @@
+
+trait Text[T]
+trait Read[A]
+object Read extends ReadImplicits:
+  implicit val unit: Read[Unit] = ???
+trait ReadImplicits:
+  import scala.deriving.*
+  given roe: Read[Option[EmptyTuple]] = ???
+  given rou: Read[Option[Unit]] = ???
+  given cons1[H, T <: Tuple](using Read[Option[H]], Read[Option[T]]): Read[Option[H *: T]] = ???
+
+trait Fragment:
+  def query[B: Read]: String = ???
+
+@main def Test =
+  val f: Fragment = ???
+  f.query // was error