From cc8399dc41ca47a48ad99dc07a18f0a3009bbe4a Mon Sep 17 00:00:00 2001
From: Andy <anhans@microsoft.com>
Date: Wed, 26 Jul 2017 16:00:34 -0700
Subject: [PATCH] Escape string literal before looking it up in enum's symbol
 table (#17441)

---
 src/compiler/checker.ts                          |  2 +-
 .../reference/underscoreEscapedNameInEnum.js     | 13 +++++++++++++
 .../underscoreEscapedNameInEnum.symbols          | 10 ++++++++++
 .../reference/underscoreEscapedNameInEnum.types  | 16 ++++++++++++++++
 .../compiler/underscoreEscapedNameInEnum.ts      |  4 ++++
 5 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/underscoreEscapedNameInEnum.js
 create mode 100644 tests/baselines/reference/underscoreEscapedNameInEnum.symbols
 create mode 100644 tests/baselines/reference/underscoreEscapedNameInEnum.types
 create mode 100644 tests/cases/compiler/underscoreEscapedNameInEnum.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f2b9d50db91..bf1cc33d159 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -21517,7 +21517,7 @@ namespace ts {
                                 else {
                                     const argument = ex.argumentExpression;
                                     Debug.assert(isLiteralExpression(argument));
-                                    name = (argument as LiteralExpression).text as __String; // TODO: GH#17348
+                                    name = escapeLeadingUnderscores((argument as LiteralExpression).text);
                                 }
                                 return evaluateEnumMember(expr, type.symbol, name);
                             }
diff --git a/tests/baselines/reference/underscoreEscapedNameInEnum.js b/tests/baselines/reference/underscoreEscapedNameInEnum.js
new file mode 100644
index 00000000000..db40f126739
--- /dev/null
+++ b/tests/baselines/reference/underscoreEscapedNameInEnum.js
@@ -0,0 +1,13 @@
+//// [underscoreEscapedNameInEnum.ts]
+enum E {
+    "__foo" = 1,
+    bar = E["__foo"] + 1
+}
+
+
+//// [underscoreEscapedNameInEnum.js]
+var E;
+(function (E) {
+    E[E["__foo"] = 1] = "__foo";
+    E[E["bar"] = 2] = "bar";
+})(E || (E = {}));
diff --git a/tests/baselines/reference/underscoreEscapedNameInEnum.symbols b/tests/baselines/reference/underscoreEscapedNameInEnum.symbols
new file mode 100644
index 00000000000..4546d844cd2
--- /dev/null
+++ b/tests/baselines/reference/underscoreEscapedNameInEnum.symbols
@@ -0,0 +1,10 @@
+=== tests/cases/compiler/underscoreEscapedNameInEnum.ts ===
+enum E {
+>E : Symbol(E, Decl(underscoreEscapedNameInEnum.ts, 0, 0))
+
+    "__foo" = 1,
+    bar = E["__foo"] + 1
+>bar : Symbol(E.bar, Decl(underscoreEscapedNameInEnum.ts, 1, 16))
+>E : Symbol(E, Decl(underscoreEscapedNameInEnum.ts, 0, 0))
+}
+
diff --git a/tests/baselines/reference/underscoreEscapedNameInEnum.types b/tests/baselines/reference/underscoreEscapedNameInEnum.types
new file mode 100644
index 00000000000..02fc9a5493c
--- /dev/null
+++ b/tests/baselines/reference/underscoreEscapedNameInEnum.types
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/underscoreEscapedNameInEnum.ts ===
+enum E {
+>E : E
+
+    "__foo" = 1,
+>1 : 1
+
+    bar = E["__foo"] + 1
+>bar : E
+>E["__foo"] + 1 : number
+>E["__foo"] : E
+>E : typeof E
+>"__foo" : "__foo"
+>1 : 1
+}
+
diff --git a/tests/cases/compiler/underscoreEscapedNameInEnum.ts b/tests/cases/compiler/underscoreEscapedNameInEnum.ts
new file mode 100644
index 00000000000..ef16f253dd7
--- /dev/null
+++ b/tests/cases/compiler/underscoreEscapedNameInEnum.ts
@@ -0,0 +1,4 @@
+enum E {
+    "__foo" = 1,
+    bar = E["__foo"] + 1
+}