Rewrite xs.to => xs.to(CC) (fix #106)

scalafix/input/src/main/scala/fix/TraversableSrc.scala

@@ -14,5 +14,5 @@ object TraversableSrc {
   def m1(xs: Traversable[Int]): List[Int] =
     xs.to
 
-  def m2(xs: Traversable[Int]): List[Int] = xs.to
+  List[Int]() // unrelated matching brackets
 }

scalafix/output212/src/main/scala/fix/TraversableSrc.scala

@@ -13,7 +13,7 @@ object TraversableSrc {
   }
 
   def m1(xs: Iterable[Int]): List[Int] =
-    xs.to
+    xs.to(scala.collection.immutable.List)
 
-  def m2(xs: Iterable[Int]): List[Int] = xs.to
+  List[Int]() // unrelated matching brackets
 }

scalafix/rules/src/main/scala/fix/Stable212Base.scala

@@ -185,6 +185,32 @@ trait Stable212Base extends CrossCompatibility { self: SemanticRule =>
     else Patch.empty
   }
 
+   def extractCollection(toCol: Tree): String = {
+     toCol match {
+       case Term.ApplyType(q"scala.Predef.fallbackStringCanBuildFrom", _) =>
+         "scala.collection.immutable.IndexedSeq"
+       case Term.ApplyType(Term.Select(coll,_), _) =>
+         coll.syntax
+       case Term.Apply(Term.ApplyType(Term.Select(coll, _), _), _) =>
+         coll.syntax
+       case Term.Select(coll,_) =>
+         coll.syntax
+       case _ => {
+         throw new Exception(
+           s"""|cannot extract collection from .to
+               |
+               |---------------------------------------------
+               |syntax:
+               |${toCol.syntax}
+               |
+               |---------------------------------------------
+               |structure:
+               |${toCol.structure}""".stripMargin
+         )
+       }
+     }
+   }
+
   def replaceToList(ctx: RuleCtx): Patch = {
     ctx.tree.collect {
       case iterator(t: Name) =>
@@ -194,6 +220,14 @@ trait Stable212Base extends CrossCompatibility { self: SemanticRule =>
         trailingBrackets(n, ctx).map { case (open, close) =>
           ctx.replaceToken(open, "(") + ctx.replaceToken(close, ")")
         }.asPatch
+
+      case Term.Select(_, to @ toTpe(_)) =>
+        val synth = ctx.index.synthetics.find(_.position.end == to.pos.end)
+        synth.map{ s =>
+          val Term.Apply(_, List(toCol)) = s.text.parse[Term].get
+          val col = extractCollection(toCol)
+          ctx.addRight(to, "(" + col + ")")
+        }.getOrElse(Patch.empty)
     }.asPatch
   }
 

scalafix/tests/src/test/scala/fix/ScalafixTests.scala

@@ -17,5 +17,5 @@ class ScalafixTests
 
   runAllTests()
   // to run only one test:
-  // testsToRun.filter(_.filename.toNIO.getFileName.toString == "IterableSrc.scala" ).foreach(runOn)
+  // testsToRun.filter(_.filename.toNIO.getFileName.toString == "Playground.scala" ).foreach(runOn)
 }