From 883385f5cb321fc8008e5d4f3727412fee41d0dc Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Thu, 22 Jan 2015 11:03:15 -0800
Subject: [PATCH] Include missing optional properties in contextually typed
 object literal

---
 src/compiler/checker.ts | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 1e84c78fce1..a3ea14dcb09 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5455,6 +5455,16 @@ module ts {
                 }
             }
 
+            // If object literal is contextually typed, add missing optional properties from the contextual type
+            // such that the resulting type becomes a subtype in cases where only optional properties were omitted
+            if (contextualType) {
+                forEach(getPropertiesOfObjectType(contextualType), p => {
+                    if (p.flags & SymbolFlags.Optional && !hasProperty(properties, p.name)) {
+                        properties[p.name] = p;
+                    }
+                });
+            }
+
             var stringIndexType = getIndexType(IndexKind.String);
             var numberIndexType = getIndexType(IndexKind.Number);
             var result = createAnonymousType(node.symbol, properties, emptyArray, emptyArray, stringIndexType, numberIndexType);