io_lib:char_list predicate

Summary: - supporting narrowing `case io_lib:char_list(T) of`

Reviewed By: michalmuskala

Differential Revision: D66964528

fbshipit-source-id: 5465948ec1b221f811aca6d753bf57860f210779

Author: ilya-klyuchnikov

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

@@ -71,7 +71,11 @@ class ElabApplyCustom(pipelineContext: PipelineContext) {
     else Set()
 
   private lazy val customPredicate: Set[RemoteId] =
-    Set(RemoteId("lists", "member", 2))
+    Set(
+      RemoteId("io_lib", "char_list", 1),
+      RemoteId("io_lib", "latin1_char_list", 1),
+      RemoteId("lists", "member", 2),
+    )
 
   def isCustomPredicate(id: RemoteId): Boolean =
     customPredicate(id)
@@ -608,6 +612,15 @@ class ElabApplyCustom(pipelineContext: PipelineContext) {
           case _ =>
             (booleanType, env1, env1)
         }
+      case RemoteId("io_lib", "char_list" | "latin1_char_list", 1) =>
+        val List(arg) = args
+        arg match {
+          case Var(x) =>
+            val posEnv = env1.updated(x, stringType)
+            (booleanType, posEnv, env1)
+          case _ =>
+            (booleanType, env1, env1)
+        }
       case rid =>
         throw new IllegalArgumentException(s"unexpected $rid")
     }