Quick-fix non-idempotent code generated by pattern match

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -3,7 +3,7 @@ package transform
 
 import core._
 import MegaPhase._
-import collection.mutable
+import scala.collection.mutable
 import SymDenotations._, Symbols._, Contexts._, Types._, Names._, StdNames._, NameOps._
 import ast.Trees._
 import util.Positions._
@@ -629,7 +629,9 @@ object PatternMatcher {
      *  Propagate common variable bindings as parameters into case labels.
      */
     private def mergeVars(plan: Plan): Plan = {
+      val RHSs = mutable.LinkedHashSet.empty[RHS]
       class RHS(val tree: Tree) {
+        RHSs += this
         override def equals(that: Any) = that match {
           case that: RHS => this.tree === that.tree
           case _ => false
@@ -700,7 +702,8 @@ object PatternMatcher {
           }
           val newArgs =
             for {
-              (rhs, actual) <- seenVars.toList
+              rhs <- RHSs.toList
+              actual <- seenVars.get(rhs)
               formal <- paramsOfLabel(plan.label).get(rhs)
             }
             yield (formal -> actual)