Add regression tests for #21352 and ..

* `neandertech/langoustine` - [#21344 (comment)]
(#21344 (comment))
* `tpolcat/doobie` - [#21344 (comment)]
(#21344 (comment))

Fixes #21352

[Cherry-picked 5408a80]

tests/pos/i21352a/schema.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/schemaDerivation.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/i21352b.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/i21352c.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