Rule for symbolic foldLeft(/:) and foldRight(:/) (fix #27)

Author: MasseGuillaume

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

@@ -0,0 +1,12 @@
+/*
+rule = "scala:fix.Scalacollectioncompat_NewCollections"
+ */
+package fix
+
+class FoldSrc(xs: List[Int]){
+  val f: (Int, Int) => Int = (x, y) => x + y
+  val g: (Int, Int) => Int = (x, y) => x * y
+
+  (0 /: xs)(f)
+  (xs :\ 1)(g)
+}

scalafix/output/src/main/scala/fix/FoldSrc.scala

@@ -0,0 +1,12 @@
+
+
+
+package fix
+
+class FoldSrc(xs: List[Int]){
+  val f: (Int, Int) => Int = (x, y) => x + y
+  val g: (Int, Int) => Int = (x, y) => x * y
+
+  xs.foldLeft(0)(f)
+  xs.foldRight(1)(g)
+}

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

@@ -29,6 +29,15 @@ case class Scalacollectioncompat_NewCollections(index: SemanticdbIndex)
     Symbol("_root_.scala.runtime.Tuple2Zipped.Ops.zipped."),
     Symbol("_root_.scala.runtime.Tuple3Zipped.Ops.zipped.")
   )
+  def foldSymbol(isLeft: Boolean): SymbolMatcher = {
+    val op = 
+      if (isLeft) "/:"
+      else ":\\"
+
+    SymbolMatcher.normalized(Symbol(s"_root_.scala.collection.TraversableOnce.`$op`."))
+  }
+  val foldLeftSymbol = foldSymbol(isLeft = true)
+  val foldRightSymbol = foldSymbol(isLeft = false)
 
   val retain = 
     SymbolMatcher.normalized(
@@ -50,6 +59,14 @@ case class Scalacollectioncompat_NewCollections(index: SemanticdbIndex)
           ctx.replaceToken(close, "}") +
           ctx.replaceTree(n, "filterInPlace")  
         ).asPatch   
+
+  def replaceSymbolicFold(ctx: RuleCtx) = 
+    ctx.tree.collect {
+      case Term.Apply(ap @ Term.ApplyInfix(rhs, foldRightSymbol(_), _, List(lhs)), _) => 
+        ctx.replaceTree(ap, s"$rhs.foldRight($lhs)")
+
+      case Term.Apply(ap @ Term.ApplyInfix(lhs, foldLeftSymbol(_), _, List(rhs)), _) =>
+        ctx.replaceTree(ap, s"$rhs.foldLeft($lhs)")
     }.asPatch
 
   def replaceToList(ctx: RuleCtx) =
@@ -133,6 +150,7 @@ case class Scalacollectioncompat_NewCollections(index: SemanticdbIndex)
       replaceTupleZipped(ctx) +
       replaceCopyToBuffer(ctx) +
       replaceStreamAppend(ctx) +
-      replaceMutableMap(ctx)
+      replaceMutableMap(ctx) +
+      replaceSymbolicFold(ctx)
   }
 }