No unit insertion as an addition of no auto tupling

scalafix-core/shared/src/main/scala/scalafix/internal/rule/NoAutoTupling.scala

@@ -13,16 +13,29 @@ case class NoAutoTupling(index: SemanticdbIndex)
     ctx.addLeft(args.head.tokens.head, "(") +
       ctx.addRight(args.last.tokens.last, ")")
 
-  override def fix(ctx: RuleCtx): Patch = {
-    val adaptations = index.messages.toIterator.collect {
+  private[this] def insertUnit(ctx: RuleCtx, t: Term.Apply): Patch =
+    ctx.addRight(t.tokens.init.last, "()")
+
+  lazy val unitAdaptations: Set[Position] =
+    index.messages.toIterator.collect {
+      case Message(pos, _, msg)
+          if msg.startsWith("Adaptation of argument list by inserting ()") =>
+        pos
+    }.toSet
+
+  lazy val tupleAdaptations: Set[Position] =
+    index.messages.toIterator.collect {
       case Message(pos, _, msg)
           if msg.startsWith("Adapting argument list by creating a") =>
         pos
     }.toSet
 
+  override def fix(ctx: RuleCtx): Patch = {
     ctx.tree.collect {
-      case t: Term.Apply if adaptations.contains(t.pos) =>
+      case t: Term.Apply if tupleAdaptations.contains(t.pos) =>
         addWrappingParens(ctx, t.args)
+      case t: Term.Apply if t.args.isEmpty && unitAdaptations.contains(t.pos) =>
+        insertUnit(ctx, t)
     }.asPatch
   }
 }

scalafix-tests/input/src/main/scala/test/NoUnitInsertion.scala

@@ -0,0 +1,27 @@
+/*
+rules = NoAutoTupling
+ */
+package test
+
+class NoUnitInsertion {
+
+  val x: Option[Unit] = Option()
+
+  def a(u: Unit): Unit = u
+  a()
+
+  def b(x: Int)(u: Unit): Unit = (x, u)
+  b(2)()
+
+  val c: Unit => Unit =
+    u => u
+  c()
+
+  case class Foo(u: Unit)
+  Foo()
+  Foo.apply()
+
+  case class Bar(i: Int)(u: Unit)
+  Bar.apply(2)()
+
+}

scalafix-tests/output/src/main/scala/test/NoUnitInsertion.scala

@@ -0,0 +1,24 @@
+package test
+
+class NoUnitInsertion {
+
+  val x: Option[Unit] = Option(())
+
+  def a(u: Unit): Unit = u
+  a(())
+
+  def b(x: Int)(u: Unit): Unit = (x, u)
+  b(2)(())
+
+  val c: Unit => Unit =
+    u => u
+  c(())
+
+  case class Foo(u: Unit)
+  Foo(())
+  Foo.apply(())
+
+  case class Bar(i: Int)(u: Unit)
+  Bar.apply(2)(())
+
+}