From 614d171a21b5c9e95e60a6c62ecec3e97879de6f Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Sat, 16 Jul 2016 14:45:38 -0700
Subject: [PATCH] Include type parameter constrains in literal type context
 determination

---
 src/compiler/checker.ts | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 47fa9918d2b..bbe74231f5a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13007,8 +13007,22 @@ namespace ts {
                 false;
         }
 
+        function hasLiteralContextualType(node: Expression) {
+            const contextualType = getContextualType(node);
+            if (!contextualType) {
+                return false;
+            }
+            if (contextualType.flags & TypeFlags.TypeParameter) {
+                const apparentType = getApparentTypeOfTypeParameter(<TypeParameter>contextualType);
+                if (apparentType.flags & (TypeFlags.StringLike | TypeFlags.NumberLike | TypeFlags.BooleanLike)) {
+                    return true;
+                }
+            }
+            return isLiteralUnionType(contextualType);
+        }
+
         function isLiteralTypeContext(node: Expression) {
-            return isLiteralTypeLocation(node) || isLiteralUnionType(getContextualType(node) || unknownType);
+            return isLiteralTypeLocation(node) || hasLiteralContextualType(node);
         }
 
         function checkLiteralExpression(node: Expression): Type {