From 5dbe5f4fbdb7c91598441bffdee7577a71471c2c Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Wed, 16 Nov 2016 15:24:42 -0800
Subject: [PATCH] Widen literal types of parameter properties

---
 src/compiler/checker.ts   | 2 +-
 src/compiler/utilities.ts | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 7132aedb324..b466bf7afb6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -14744,7 +14744,7 @@ namespace ts {
         function checkDeclarationInitializer(declaration: VariableLikeDeclaration) {
             const type = checkExpressionCached(declaration.initializer);
             return getCombinedNodeFlags(declaration) & NodeFlags.Const ||
-                getCombinedModifierFlags(declaration) & ModifierFlags.Readonly ||
+                getCombinedModifierFlags(declaration) & ModifierFlags.Readonly && !isParameterPropertyDeclaration(declaration) ||
                 isTypeAssertion(declaration.initializer) ? type : getWidenedLiteralType(type);
         }
 
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index bfabb3b1e4a..546416884f1 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -4497,7 +4497,7 @@ namespace ts {
         }
     }
 
-    export function isParameterPropertyDeclaration(node: ParameterDeclaration): boolean {
+    export function isParameterPropertyDeclaration(node: Node): boolean {
         return hasModifier(node, ModifierFlags.ParameterPropertyModifier) && node.parent.kind === SyntaxKind.Constructor && isClassLike(node.parent.parent);
     }