From f81925992c09ceb6922f2c00e7effd6418981429 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Sun, 11 Jun 2017 14:54:36 -0700
Subject: [PATCH] Intersection with 'never' type always produces 'never'

---
 src/compiler/checker.ts | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index bbd38ddbc5d..f5aa57777da 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7168,6 +7168,7 @@ namespace ts {
             containsAny?: boolean;
             containsUndefined?: boolean;
             containsNull?: boolean;
+            containsNever?: boolean;
             containsNonWideningType?: boolean;
             containsString?: boolean;
             containsNumber?: boolean;
@@ -7369,10 +7370,13 @@ namespace ts {
             else if (type.flags & TypeFlags.Any) {
                 typeSet.containsAny = true;
             }
+            else if (type.flags & TypeFlags.Never) {
+                typeSet.containsNever = true;
+            }
             else if (getObjectFlags(type) & ObjectFlags.Anonymous && isEmptyObjectType(type)) {
                 typeSet.containsEmptyObject = true;
             }
-            else if (!(type.flags & TypeFlags.Never) && (strictNullChecks || !(type.flags & TypeFlags.Nullable)) && !contains(typeSet, type)) {
+            else if ((strictNullChecks || !(type.flags & TypeFlags.Nullable)) && !contains(typeSet, type)) {
                 if (type.flags & TypeFlags.Object) {
                     typeSet.containsObjectType = true;
                 }
@@ -7410,6 +7414,9 @@ namespace ts {
             }
             const typeSet = [] as TypeSet;
             addTypesToIntersection(typeSet, types);
+            if (typeSet.containsNever) {
+                return neverType;
+            }
             if (typeSet.containsAny) {
                 return anyType;
             }