bug fix for maps:fold

Summary: - bug fix: checking that the lambda arity is 3

Reviewed By: TD5

Differential Revision: D76293253

fbshipit-source-id: df7fde8174b5e125ea848f69a2c7d471c082cfa2

Author: ilya-klyuchnikov

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/tc/ElabApplyCustom.scala

@@ -309,10 +309,10 @@ class ElabApplyCustom(pipelineContext: PipelineContext) {
         def isShapeIterator(lambda: Lambda): Boolean = {
           val lastClauseIndex = lambda.clauses.length - 1
           lambda.clauses.zipWithIndex forall { (clause, index) =>
-            clause.pats.head match {
-              case PatVar(_) if index == lastClauseIndex =>
+            clause.pats match {
+              case List(PatVar(_), _, _) if index == lastClauseIndex =>
                 true
-              case PatAtom(_) =>
+              case List(PatAtom(_), _, _) =>
                 true
               case _ =>
                 false