From fc6947b081a7e2e649f12ed9f6e86942733a3970 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 20 Jan 2016 16:51:48 -0800
Subject: [PATCH] Make get only accessor compatible with writable property in
 type relationships

---
 src/compiler/checker.ts | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0f880cd17f9..465411e0c68 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -10412,19 +10412,13 @@ namespace ts {
         }
 
         function isReadonlySymbol(symbol: Symbol): boolean {
-            if (symbol.flags & SymbolFlags.Property) {
-                return symbol === undefinedSymbol || (getDeclarationFlagsFromSymbol(symbol) & NodeFlags.Readonly) !== 0;
-            }
-            if (symbol.flags & SymbolFlags.Accessor) {
-                return !(symbol.flags & SymbolFlags.SetAccessor);
-            }
-            return false;
+            return symbol.flags & SymbolFlags.Property && (getDeclarationFlagsFromSymbol(symbol) & NodeFlags.Readonly) !== 0;
         }
 
         function isConstantSymbol(symbol: Symbol): boolean {
-            if (symbol.flags & SymbolFlags.Variable) {
-                return (getDeclarationFlagsFromSymbol(symbol) & NodeFlags.Const) !== 0;
-            }
+            return symbol === undefinedSymbol ||
+                symbol.flags & SymbolFlags.Variable && (getDeclarationFlagsFromSymbol(symbol) & NodeFlags.Const) !== 0 ||
+                symbol.flags & SymbolFlags.Accessor && !(symbol.flags & SymbolFlags.SetAccessor);
         }
 
         function checkReferenceExpression(expr: Expression, invalidReferenceMessage: DiagnosticMessage, constantVariableMessage: DiagnosticMessage): boolean {
@@ -15723,7 +15717,6 @@ namespace ts {
 
             // Initialize special types
             globalArrayType = <GenericType>getGlobalType("Array", /*arity*/ 1);
-            globalReadonlyArrayType = <GenericType>getGlobalType("ReadonlyArray", /*arity*/ 1);
             globalObjectType = getGlobalType("Object");
             globalFunctionType = getGlobalType("Function");
             globalStringType = getGlobalType("String");
@@ -15768,8 +15761,10 @@ namespace ts {
             }
 
             anyArrayType = createArrayType(anyType);
-            anyReadonlyArrayType = globalReadonlyArrayType === emptyGenericType ? anyArrayType :
-                createTypeFromGenericGlobalType(globalReadonlyArrayType, [anyType]);
+
+            const symbol = getGlobalSymbol("ReadonlyArray", SymbolFlags.Type, /*diagnostic*/ undefined);
+            globalReadonlyArrayType = symbol && <GenericType>getTypeOfGlobalSymbol(symbol, /*arity*/ 1);
+            anyReadonlyArrayType = globalReadonlyArrayType ? createTypeFromGenericGlobalType(globalReadonlyArrayType, [anyType]) : anyArrayType;
         }
 
         function createInstantiatedPromiseLikeType(): ObjectType {