From f6a3a3fc3dc5aac5d5b1bbec8a64656be6cbda85 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 14 Feb 2017 12:04:39 -0800
Subject: [PATCH] Use '__this__' property in contextual type to indicate type
 of 'this'

---
 src/compiler/checker.ts | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 2b059e29d09..1f59d28cc7c 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11189,6 +11189,19 @@ namespace ts {
                         return getTypeOfSymbol(thisParameter);
                     }
                 }
+                if (isObjectLiteralMethod(func)) {
+                    // For methods in an object literal, look for a '__this__' property in the contextual
+                    // type for the object literal. If one exists, remove 'undefined' from the type of that
+                    // property and report it as the contextual type for 'this' in the method.
+                    const objectLiteral = <ObjectLiteralExpression>func.parent;
+                    const type = getApparentTypeOfContextualType(objectLiteral);
+                    if (type) {
+                        const propertyType = getTypeOfPropertyOfContextualType(type, "___this__");
+                        if (propertyType) {
+                            return getNonNullableType(propertyType);
+                        }
+                    }
+                }
             }
             return undefined;
         }