Limit when companion extends FunctionN

NOTICE

@@ -1,5 +1,5 @@
 scalaz-deriving
-Copyright 2017 - 2018 Sam Halliday
+Copyright 2017 - 2019 Sam Halliday
 
 This project is licensed under the terms of the LGPL 3.0 or any later
 version, see LICENSE.

deriving-plugin/src/main/scala/scalaz/plugins/deriving/AnnotationPlugin.scala

@@ -7,7 +7,7 @@ package scalaz.plugins.deriving
 
 import scala.Predef.ArrowAssoc
 import scala.deprecated
-import scala.collection.immutable.Map
+import scala.collection.immutable.{ Map, StringOps }
 import scala.collection.breakOut
 import scala.reflect.internal.util._
 import scala.tools.nsc._
@@ -55,10 +55,50 @@ abstract class AnnotationPlugin(override val global: Global) extends Plugin {
   def isIde: Boolean      = global.isInstanceOf[tools.nsc.interactive.Global]
   def isScaladoc: Boolean = global.isInstanceOf[tools.nsc.doc.ScaladocGlobal]
 
+  private case class PrettyPrinter(
+    level: Int,
+    inQuotes: Boolean,
+    backslashed: Boolean
+  ) {
+    val indent = List.fill(level)("  ").mkString
+
+    def transform(char: Char): (PrettyPrinter, String) = {
+      val (pp, f): (PrettyPrinter, PrettyPrinter => String) = char match {
+        case '"' if inQuotes && !backslashed =>
+          (copy(inQuotes = false), _ => s"$char")
+        case '"' if !inQuotes => (copy(inQuotes = true), _ => s"$char")
+        case '\\' if inQuotes && !backslashed =>
+          (copy(backslashed = true), _ => s"$char")
+
+        case ',' if !inQuotes => (this, p => s",\n${p.indent}")
+        case '(' if !inQuotes =>
+          (copy(level = level + 1), p => s"(\n${p.indent}")
+        case ')' if !inQuotes =>
+          (copy(level = level - 1), p => s"\n${p.indent})")
+        case _ => (this, _ => s"$char")
+      }
+      (pp, f(pp))
+    }
+  }
+
+  private def prettyPrint(raw: String): String =
+    new StringOps(raw)
+      .foldLeft((PrettyPrinter(0, false, false), new StringBuilder(""))) {
+        case ((pp, sb), char) =>
+          val (newPP, res) = pp.transform(char)
+          (newPP, sb.append(res))
+      }
+      ._2
+      .toString
+      .replaceAll("""\(\s+\)""", "()")
+
+  private def showTree(tree: Tree, pretty: Boolean): String =
+    if (pretty) prettyPrint(showRaw(tree)) else showRaw(tree)
+
   // best way to inspect a tree, just call this
-  def debug(name: String, tree: Tree): Unit =
+  def debug(name: String, tree: Tree, pretty: Boolean = false): Unit =
     Predef.println(
-      s"====\n$name ${tree.id} ${tree.pos}:\n${showCode(tree)}\n${showRaw(tree)}"
+      s"====\n$name ${tree.id} ${tree.pos}:\n${showCode(tree)}\n${showTree(tree, pretty)}"
     )
 
   // recovers the final part of an annotation
@@ -139,6 +179,20 @@ abstract class AnnotationPlugin(override val global: Global) extends Plugin {
       case _                                           => false
     }
 
+    private def getConstructor(clazz: ClassDef): Option[DefDef] =
+      clazz.impl.collect {
+        case d @ DefDef(_, nme.CONSTRUCTOR, _, _, _, _) => d
+      }.headOption
+
+    // A simple constructor is one with only one parameter group and no implicit parameters
+    private def hasSimpleConstructor(clazz: ClassDef): Boolean =
+      getConstructor(clazz) match {
+        case Some(DefDef(_, _, _, ps :: Nil, _, _))
+            if !ps.exists(_.mods.hasFlag(Flag.IMPLICIT)) =>
+          true
+        case _ => false
+      }
+
     /** generates a zero-functionality companion for a class */
     private def genCompanion(clazz: ClassDef): ModuleDef = {
       val mods =
@@ -158,6 +212,7 @@ abstract class AnnotationPlugin(override val global: Global) extends Plugin {
       def sup =
         if (isCase &&
             clazz.tparams.isEmpty &&
+            hasSimpleConstructor(clazz) &&
             addSuperFunction(clazz) &&
             accessors.size <= 22) {
           AppliedTypeTree(