Suppress additional warnings existing in the LTS due to rejection of #17548 backport

Author: WojciechMazur

community-build/community-projects/scodec

@@ -368,7 +368,10 @@ object projects:
 
   lazy val shapeless3 = SbtCommunityProject(
     project = "shapeless-3",
-    sbtTestCommand = "testJVM; testJS",
+    sbtTestCommand = List(
+      """set derivingJVM/scalacOptions += "-Wconf:msg=New anonymous class definition will be duplicated at each inline site:s" """,
+      """set derivingJS/scalacOptions += "-Wconf:msg=New anonymous class definition will be duplicated at each inline site:s" """,
+      "testJVM", "testJS").mkString("; "),
     sbtDocCommand = forceDoc("typeable", "deriving"),
     scalacOptions = SbtCommunityProject.scalacOptions.filter(_ != "-Ysafe-init"), // due to -Xfatal-warnings
   )

community-build/src/scala/dotty/communitybuild/projects.scala

@@ -0,0 +1,14 @@
+// LTS specifc, not applicable to Next thanks to #17548 improvements
+trait Empty[T]:
+  def empty: T
+
+object Empty:
+  inline def withOnly[F[_], R, T](f: [t <: T] => F[t] => R): R = f(null.asInstanceOf[F[T]])
+
+  def mkEmpty[T](t: T): Empty[T] = ???
+
+  inline given emptyGenC[A]: Empty[A] =
+    mkEmpty(withOnly[Empty, A, A]([a <: A] => (_: Empty[a]).empty)) // warn
+
+@main def Test =
+  Empty.emptyGenC[String]