From b9efe3e700deb7f4558caae0ed41ac143c2b3663 Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Thu, 18 May 2017 13:57:24 -0700
Subject: [PATCH] Retain undefined in spreads w/strictNullChecks

Previously, both optional and `| undefined` caused spread properties to
combine with preceding properties and drop the `undefined`. Now, with
strictNullChecks, optional and `| undefined` properties still combine
with preceding properties but don't drop the `undefined`.
---
 src/compiler/checker.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index dde8033d1e..e4ea3740a6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7640,11 +7640,11 @@ namespace ts {
                 if (members.has(leftProp.name)) {
                     const rightProp = members.get(leftProp.name);
                     const rightType = getTypeOfSymbol(rightProp);
-                    if (maybeTypeOfKind(rightType, TypeFlags.Undefined) || rightProp.flags & SymbolFlags.Optional) {
+                    if (rightProp.flags & SymbolFlags.Optional) {
                         const declarations: Declaration[] = concatenate(leftProp.declarations, rightProp.declarations);
                         const flags = SymbolFlags.Property | (leftProp.flags & SymbolFlags.Optional);
                         const result = createSymbol(flags, leftProp.name);
-                        result.type = getUnionType([getTypeOfSymbol(leftProp), getTypeWithFacts(rightType, TypeFacts.NEUndefined)]);
+                        result.type = getUnionType([getTypeOfSymbol(leftProp), rightType]);
                         result.leftSpread = leftProp;
                         result.rightSpread = rightProp;
                         result.declarations = declarations;