Escape string literal before looking it up in enum's symbol table (#17441)

Author: Andy

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);
                             }

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 = {}));

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))
+}
+

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
+}
+

tests/cases/compiler/underscoreEscapedNameInEnum.ts

@@ -0,0 +1,4 @@
+enum E {
+    "__foo" = 1,
+    bar = E["__foo"] + 1
+}