Minimalist attempt to reproduce scala 3 compile error

scala/scala3#18555

branch:

Author: SamTheisens

.gitignore

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+### SBT template
+# Simple Build Tool
+# http://www.scala-sbt.org/release/docs/Getting-Started/Directories.html#configuring-version-control
+
+dist/*
+target/
+lib_managed/
+src_managed/
+project/boot/
+project/plugins/project/
+.history
+.cache
+.lib/
+
+.idea/
+.bsp/

.scalafmt.conf

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+version = 2.7.5

build.sbt

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+val scala3 = "3.3.0-RC1-bin-20221214-6383025-NIGHTLY"
+lazy val `ReactiveMongo-Core` = project
+  .in(file("core"))
+  .settings(
+    name := "ReactiveMongo-Core",
+    description := "Example sbt project that compiles using Scala 3",
+    version := "0.1.0",
+    scalaVersion := scala3,
+    scalacOptions ++= Seq("-deprecation"),
+  )
+
+
+lazy val `ReactiveMongo` = project
+  .in(file("driver"))
+  .settings(
+    name := "ReactiveMongo",
+    description := "Example sbt project that compiles using Scala 3",
+    version := "0.1.0",
+    scalaVersion := scala3,
+    scalacOptions ++= Seq("-deprecation"),
+  ).dependsOn(`ReactiveMongo-Core`)

core/src/main/scala-2/api/SerializationPackCompat.scala

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+package reactivemongo.api
+
+private[api] trait SerializationPackCompat {
+  _: Singleton with SerializationPack =>
+
+  val IdentityWriter: Writer[Document]
+  val IdentityReader: Reader[Document]
+}

core/src/main/scala-3/api/SerializationPackCompat.scala

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+package reactivemongo.api
+
+
+private[api] trait SerializationPackCompat {
+  _self: Singleton with SerializationPack =>
+
+  lazy val IdentityWriter: Writer[Document]
+  lazy val IdentityReader: Reader[Document]
+}

core/src/main/scala/api/GenericCollectionWithCommands.scala

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+package reactivemongo.api
+
+
+trait SerializationPack extends SerializationPackCompat {
+  self: Singleton =>
+  type Value
+  type Document <: Value
+  type Writer[A]
+  type Reader[A]
+}

driver/src/main/scala/Main.scala

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+
+@main
+def Main(args: String*): Unit = {
+	println("hello world")
+}

driver/src/main/scala/api/GenericCollectionWithCommands.scala

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+package reactivemongo.api.collections
+
+import collections.GenericCollection
+import reactivemongo.api.SerializationPack
+
+
+
+
+
+trait GenericCollectionWithCommands[P <: SerializationPack] {
+  self: GenericCollection[P] =>
+
+}

driver/src/main/scala/api/PackSupport.scala

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+package reactivemongo.api
+
+trait PackSupport[P <: SerializationPack] {
+
+  /**
+   * The serialization pack ([[https://javadoc.io/doc/org.reactivemongo/reactivemongo-bson-api_2.12/latest/index.html BSON]] by default).
+   *
+   * Used to resolve the types of values
+   * (by default `BSONValue`, `BSONDocument`, ...), and the related typeclasses
+   * (e.g. `BSONDocumentReader` ...).
+   */
+  val pack: P
+}

driver/src/main/scala/collections/GenericCollection.scala

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+package collections
+
+import reactivemongo.api.PackSupport
+import reactivemongo.api.SerializationPack
+import reactivemongo.api.collections.GenericCollectionWithCommands
+
+trait GenericCollection[P <: SerializationPack]
+    extends GenericCollectionWithCommands[P]
+    with PackSupport[P] {
+  self =>
+  private implicit def packIdentityWriter
+      : pack.Writer[pack.Document] =
+    pack.IdentityWriter
+}

project/build.properties

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+sbt.version=1.9.4