Rewrite collection.Set.+ restrict type of lhs

scalafix allow us to match on SetLike.+ but we cannot check the type of the expression on the lhs

We can work arround this limitation if the lhs is a identifier (simple case). This allow us
to document the expected type on the lhs and prepare the implementation once scalameta/scalameta#1212 is resolved

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

@@ -15,7 +15,9 @@ class SetMapSrc(iset: immutable.Set[Int],
   imap + (2 -> 3, 3 -> 4)
   (iset + (2, 3)).toString
   iset + (2, 3) - 4
-  iset + 1 - 2
-  cset + 1 - 2
+  iset + 1
+  iset - 2
+  cset + 1
+  cset - 2
   cmap + (2 -> 3) + ((4, 5))
 }

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

@@ -15,7 +15,9 @@ class SetMapSrc(iset: immutable.Set[Int],
   imap + (2 -> 3) + (3 -> 4)
   (iset + 2 + 3).toString
   iset + 2 + 3 - 4
-  iset + 1 - 2
-  cset ++ _root_.scala.collection.Set(1) -- _root_.scala.collection.Set(2)
+  iset + 1
+  iset - 2
+  cset ++ _root_.scala.collection.Set(1)
+  cset -- _root_.scala.collection.Set(2)
   cmap ++ _root_.scala.collection.Map(2 -> 3) ++ _root_.scala.collection.Map((4, 5))
 }

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

@@ -222,6 +222,15 @@ case class Scalacollectioncompat_newcollections(index: SemanticdbIndex)
     }.asPatch
   }
 
+  // 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)
+
+  def isCollectionSet(tree: Tree, ctx: RuleCtx): Boolean =
+    isTpe(Symbol("_root_.scala.collection.Set#"), tree, ctx)
+
   def replaceSetMapPlusMinus(ctx: RuleCtx): Patch = {
     def rewriteOp(op: Tree, rhs: Tree, doubleOp: String, col0: String): Patch = {
       val col = "_root_.scala.collection." + col0
@@ -238,10 +247,10 @@ case class Scalacollectioncompat_newcollections(index: SemanticdbIndex)
     }
 
     ctx.tree.collect {
-      case Term.ApplyInfix(_, op @ setPlus(_), Nil, List(rhs)) =>
+      case Term.ApplyInfix(lhs, op @ setPlus(_), Nil, List(rhs)) if isCollectionSet(lhs, ctx) =>
         rewriteOp(op, rhs, "+", "Set")
 
-      case Term.ApplyInfix(lhs, op @ setMinus(_), Nil, List(rhs)) =>
+      case Term.ApplyInfix(lhs, op @ setMinus(_), Nil, List(rhs)) if isCollectionSet(lhs, ctx) =>
         rewriteOp(op, rhs, "-", "Set")
 
       case Term.ApplyInfix(lhs, op @ mapPlus(_), Nil, List(rhs)) =>