From b17e75b52b99b4fa793a4f46eadde63d87d6fe2c Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 24 Oct 2017 13:27:55 -0700
Subject: [PATCH] Missing properties in fresh object literals are known to be
 undefined

---
 src/compiler/checker.ts           | 9 +++++++++
 src/compiler/commandLineParser.ts | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index aaaa0ed50b8..4e1f14974fe 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -9604,6 +9604,15 @@ namespace ts {
                     }
                     return Ternary.False;
                 }
+                if (relation === subtypeRelation && target.flags & TypeFlags.FreshLiteral) {
+                    const excessProperty = getUnmatchedProperty(target, source, /*requireOptionalProperties*/ true);
+                    if (excessProperty) {
+                        if (reportErrors) {
+                            reportError(Diagnostics.Property_0_does_not_exist_on_type_1, symbolToString(excessProperty), typeToString(target));
+                        }
+                        return Ternary.False;
+                    }
+                }
                 let result = Ternary.True;
                 const properties = getPropertiesOfObjectType(target);
                 for (const targetProp of properties) {
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index f050c4a5d16..27b2d9f5087 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -1273,7 +1273,7 @@ namespace ts {
             return result;
         }
 
-        function getDefaultValueForOption(option: CommandLineOption) {
+        function getDefaultValueForOption(option: CommandLineOption): {} {
             switch (option.type) {
                 case "number":
                     return 1;