From 204f2c16c0d6ff851e4798c03a9646b625ac2bd7 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Wed, 3 Aug 2016 08:55:55 -0700
Subject: [PATCH] Add a helper function `getOrUpdateProperty` to prevent
 unprotected access to Maps.

---
 src/compiler/core.ts                             | 10 +++++++---
 src/compiler/emitter.ts                          |  2 +-
 tests/baselines/reference/exportToString.js      |  9 +++++++++
 tests/baselines/reference/exportToString.symbols |  7 +++++++
 tests/baselines/reference/exportToString.types   |  8 ++++++++
 tests/cases/compiler/exportToString.ts           |  2 ++
 6 files changed, 34 insertions(+), 4 deletions(-)
 create mode 100644 tests/baselines/reference/exportToString.js
 create mode 100644 tests/baselines/reference/exportToString.symbols
 create mode 100644 tests/baselines/reference/exportToString.types
 create mode 100644 tests/cases/compiler/exportToString.ts

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 709a331e02281..6c87ad82955c3 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -323,8 +323,12 @@ namespace ts {
         return keys;
     }
 
-    export function getProperty<T>(map: Map<T>, key: string): T {
-        return hasOwnProperty.call(map, key) ? map[key] : undefined;
+    export function getProperty<T>(map: Map<T>, key: string): T | undefined {
+        return hasProperty(map, key) ? map[key] : undefined;
+    }
+
+    export function getOrUpdateProperty<T>(map: Map<T>, key: string, makeValue: () => T): T {
+        return hasProperty(map, key) ? map[key] : map[key] = makeValue();
     }
 
     export function isEmpty<T>(map: Map<T>) {
@@ -941,7 +945,7 @@ namespace ts {
      *  [^./]                   # matches everything up to the first . character (excluding directory seperators)
      *  (\\.(?!min\\.js$))?     # matches . characters but not if they are part of the .min.js file extension
      */
-    const singleAsteriskRegexFragmentFiles = "([^./]|(\\.(?!min\\.js$))?)*";
+    const singleAsteriskRegexFragmentFiles = "([^./]|(\\.(?!min\\.js$))?)*";
     const singleAsteriskRegexFragmentOther = "[^/]*";
 
     export function getRegularExpressionForWildcard(specs: string[], basePath: string, usage: "files" | "directories" | "exclude") {
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 5fe5027978c78..c8bd8072b2400 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -6842,7 +6842,7 @@ const _super = (function (geti, seti) {
                                 // export { x, y }
                                 for (const specifier of (<ExportDeclaration>node).exportClause.elements) {
                                     const name = (specifier.propertyName || specifier.name).text;
-                                    (exportSpecifiers[name] || (exportSpecifiers[name] = [])).push(specifier);
+                                    getOrUpdateProperty(exportSpecifiers, name, () => []).push(specifier);
                                 }
                             }
                             break;
diff --git a/tests/baselines/reference/exportToString.js b/tests/baselines/reference/exportToString.js
new file mode 100644
index 0000000000000..190d1693c248c
--- /dev/null
+++ b/tests/baselines/reference/exportToString.js
@@ -0,0 +1,9 @@
+//// [exportToString.ts]
+const toString = 0;
+export { toString };
+
+
+//// [exportToString.js]
+"use strict";
+var toString = 0;
+exports.toString = toString;
diff --git a/tests/baselines/reference/exportToString.symbols b/tests/baselines/reference/exportToString.symbols
new file mode 100644
index 0000000000000..ce5446317a4d5
--- /dev/null
+++ b/tests/baselines/reference/exportToString.symbols
@@ -0,0 +1,7 @@
+=== tests/cases/compiler/exportToString.ts ===
+const toString = 0;
+>toString : Symbol(toString, Decl(exportToString.ts, 0, 5))
+
+export { toString };
+>toString : Symbol(toString, Decl(exportToString.ts, 1, 8))
+
diff --git a/tests/baselines/reference/exportToString.types b/tests/baselines/reference/exportToString.types
new file mode 100644
index 0000000000000..17037852f3b13
--- /dev/null
+++ b/tests/baselines/reference/exportToString.types
@@ -0,0 +1,8 @@
+=== tests/cases/compiler/exportToString.ts ===
+const toString = 0;
+>toString : number
+>0 : number
+
+export { toString };
+>toString : number
+
diff --git a/tests/cases/compiler/exportToString.ts b/tests/cases/compiler/exportToString.ts
new file mode 100644
index 0000000000000..248df036bfde9
--- /dev/null
+++ b/tests/cases/compiler/exportToString.ts
@@ -0,0 +1,2 @@
+const toString = 0;
+export { toString };