Workaround for scalacenter/scalafix#478

This commit can be reverted once the issue is closed

Author: julienrf

rules/src/main/scala/fix/Collectionstrawman_v0.scala

@@ -29,17 +29,28 @@ case class Collectionstrawman_v0(index: SemanticdbIndex)
   )
 
   def replaceExtensionMethods(ctx: RuleCtx): Patch = {
+    val visited = collection.mutable.Set.empty[String]
     val toImport = for {
       r <- ctx.index.names
       in = r.symbol.normalized
       out <- unimports.get(in).toList
+      if !visited(out.name)
     } yield {
+      visited += out.name
       val name = in.name
-      val names = name :: additionalUnimports.get(name)
-        .fold(List.empty[String])(_ :: Nil)
-      ctx.addGlobalImport(out) +
-        ctx.addGlobalImport(
-          Importer(q"scala.Predef", names.map(n => Importee.Unimport(Name(n)))))
+      def visiting(s: String): List[String] =
+        if (!visited(s)) {
+          visited += s
+          s :: Nil
+        } else Nil
+      val names = visiting(name) ::: additionalUnimports.get(name)
+        .fold(List.empty[String])(visiting)
+      if (names.isEmpty) ctx.addGlobalImport(out)
+      else {
+        ctx.addGlobalImport(out) +
+          ctx.addGlobalImport(
+            Importer(q"scala.Predef", names.map(n => Importee.Unimport(Name(n)))))
+      }
     }
     val predefUnderscore =
       if (toImport.isEmpty) Patch.empty