Rewrite: refactor isTpe into an extractor

Author: MasseGuillaume

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

@@ -5,7 +5,7 @@ package fix
 
 import scala.collection
 import scala.collection.immutable
-import scala.collection.mutable.{Map, Set} // Challenge to make shure the scoping is correct
+import scala.collection.mutable.{Map, Set} // Challenge to make sure the scoping is correct
 
 class SetMapSrc(iset: immutable.Set[Int], 
                 cset: collection.Set[Int],

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

@@ -5,7 +5,7 @@ package fix
 
 import scala.collection
 import scala.collection.immutable
-import scala.collection.mutable.{Map, Set} // Challenge to make shure the scoping is correct
+import scala.collection.mutable.{Map, Set} // Challenge to make sure the scoping is correct
 
 class SetMapSrc(iset: immutable.Set[Int], 
                 cset: collection.Set[Int],

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

@@ -224,11 +224,22 @@ case class Scalacollectioncompat_newcollections(index: SemanticdbIndex)
   // terms dont give us terms https://github.com/scalameta/scalameta/issues/1212
   // if we have a simple identifier, we can look at his definition at query it's type
   // this should be improved in future version of scalameta
-  def isTpe(symbol: Symbol, tree: Tree, ctx: RuleCtx): Boolean =
-    ctx.index.denotation(tree).map(_.names.headOption.exists(_.symbol == symbol)).getOrElse(false)
+  object TypeMatcher {
+    def apply(symbol: Symbol)(implicit index: SemanticdbIndex): TypeMatcher =
+      new TypeMatcher(symbol)(index)
+  }
+
+  final class TypeMatcher(symbol: Symbol)(implicit index: SemanticdbIndex) {
+    def unapply(tree: Tree): Option[Unit] = {
+      val typeMatches = 
+        index.denotation(tree)
+             .map(_.names.headOption.exists(_.symbol == symbol))
+             .getOrElse(false)
+      if (typeMatches) Some(()) else None
+    }
+  }
 
-  def isCollectionSet(tree: Tree, ctx: RuleCtx): Boolean =
-    isTpe(Symbol("_root_.scala.collection.Set#"), tree, ctx)
+  val CollectionSet: TypeMatcher = TypeMatcher(Symbol("_root_.scala.collection.Set#"))
 
   def replaceSetMapPlusMinus(ctx: RuleCtx): Patch = {
     def rewriteOp(op: Tree, rhs: Tree, doubleOp: String, col0: String): Patch = {
@@ -246,10 +257,10 @@ case class Scalacollectioncompat_newcollections(index: SemanticdbIndex)
     }
 
     ctx.tree.collect {
-      case Term.ApplyInfix(lhs, op @ setPlus(_), Nil, List(rhs)) if isCollectionSet(lhs, ctx) =>
+      case Term.ApplyInfix(CollectionSet(_), op @ setPlus(_), Nil, List(rhs)) =>
         rewriteOp(op, rhs, "+", "Set")
 
-      case Term.ApplyInfix(lhs, op @ setMinus(_), Nil, List(rhs)) if isCollectionSet(lhs, ctx) =>
+      case Term.ApplyInfix(CollectionSet(_), op @ setMinus(_), Nil, List(rhs)) =>
         rewriteOp(op, rhs, "-", "Set")
 
       case Term.ApplyInfix(lhs, op @ mapPlus(_), Nil, List(rhs)) =>