From e25927da57776d7d8f14baa12f4f069e20ca151a Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Tue, 17 May 2016 13:05:03 -0700
Subject: [PATCH] Unescape string literal types starting with double
 underscore.

String literal types starting with double underscore are escaped in the
parser and need to be unescaped before the type is given the string
literal as its name.
---
 src/compiler/checker.ts                                  | 9 +++++----
 .../doubleUnderStringLiteralAssignability.errors.txt     | 9 +++++++++
 .../reference/doubleUnderStringLiteralAssignability.js   | 8 ++++++++
 .../compiler/doubleUnderStringLiteralAssignability.ts    | 2 ++
 4 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 tests/baselines/reference/doubleUnderStringLiteralAssignability.errors.txt
 create mode 100644 tests/baselines/reference/doubleUnderStringLiteralAssignability.js
 create mode 100644 tests/cases/compiler/doubleUnderStringLiteralAssignability.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 6a720d947df..587235d5b8e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5138,12 +5138,13 @@ namespace ts {
         }
 
         function getStringLiteralTypeForText(text: string): StringLiteralType {
-            if (hasProperty(stringLiteralTypes, text)) {
-                return stringLiteralTypes[text];
+            const unescaped = unescapeIdentifier(text);
+            if (hasProperty(stringLiteralTypes, unescaped)) {
+                return stringLiteralTypes[unescaped];
             }
 
-            const type = stringLiteralTypes[text] = <StringLiteralType>createType(TypeFlags.StringLiteral);
-            type.text = text;
+            const type = stringLiteralTypes[unescaped] = <StringLiteralType>createType(TypeFlags.StringLiteral);
+            type.text = unescaped;
             return type;
         }
 
diff --git a/tests/baselines/reference/doubleUnderStringLiteralAssignability.errors.txt b/tests/baselines/reference/doubleUnderStringLiteralAssignability.errors.txt
new file mode 100644
index 00000000000..782f022faeb
--- /dev/null
+++ b/tests/baselines/reference/doubleUnderStringLiteralAssignability.errors.txt
@@ -0,0 +1,9 @@
+tests/cases/compiler/doubleUnderStringLiteralAssignability.ts(2,5): error TS2322: Type '"no_dunder"' is not assignable to type '"__dunder"'.
+
+
+==== tests/cases/compiler/doubleUnderStringLiteralAssignability.ts (1 errors) ====
+    var shouldBeOk: '__dunder' = '__dunder';
+    var bad: '__dunder' = 'no_dunder';
+        ~~~
+!!! error TS2322: Type '"no_dunder"' is not assignable to type '"__dunder"'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/doubleUnderStringLiteralAssignability.js b/tests/baselines/reference/doubleUnderStringLiteralAssignability.js
new file mode 100644
index 00000000000..7911c3766e1
--- /dev/null
+++ b/tests/baselines/reference/doubleUnderStringLiteralAssignability.js
@@ -0,0 +1,8 @@
+//// [doubleUnderStringLiteralAssignability.ts]
+var shouldBeOk: '__dunder' = '__dunder';
+var bad: '__dunder' = 'no_dunder';
+
+
+//// [doubleUnderStringLiteralAssignability.js]
+var shouldBeOk = '__dunder';
+var bad = 'no_dunder';
diff --git a/tests/cases/compiler/doubleUnderStringLiteralAssignability.ts b/tests/cases/compiler/doubleUnderStringLiteralAssignability.ts
new file mode 100644
index 00000000000..81149acc992
--- /dev/null
+++ b/tests/cases/compiler/doubleUnderStringLiteralAssignability.ts
@@ -0,0 +1,2 @@
+var shouldBeOk: '__dunder' = '__dunder';
+var bad: '__dunder' = 'no_dunder';