better env propagation for (fun (...) end)(...)

Summary:
for `(fun () -> .... end)()` propagate type environments.
Needed for proper type-checking of asserts.

 ---

To do the same `(fun (Param1, ...) -> .... end)(Arg1, ...)` - more care should be taken about bound/unbound vars. - Probably in next diffs...

Reviewed By: VLanvin

Differential Revision: D77861607

fbshipit-source-id: 52f1647827e16f499a23556f7b21f9305eca78f2

Author: ilya-klyuchnikov

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

@@ -178,12 +178,13 @@ final class Elab(pipelineContext: PipelineContext) {
             (DynamicType, env1)
           case _ =>
             val envs = occurrence.clausesEnvs(l.clauses, argTys, env1)
-            val (resTys, _) =
+            val (resTys, resEnvs) =
               l.clauses
                 .lazyZip(envs)
                 .map((clause, occEnv) => elabClause(clause, argTys, occEnv, Set.empty))
                 .unzip
-            (subtype.join(resTys), env1)
+            val resEnv = if (args.isEmpty) subtype.joinEnvs(resEnvs) else env1
+            (subtype.join(resTys), resEnv)
         }
       case DynCall(DynRemoteFun(mod, name), args) =>
         val env1 = check.checkExpr(mod, AtomType, env)