Allow to use a const in the initializer of a const enum

src/compiler/checker.ts

@@ -21859,8 +21859,10 @@ namespace ts {
                         return +(<NumericLiteral>expr).text;
                     case SyntaxKind.ParenthesizedExpression:
                         return evaluate((<ParenthesizedExpression>expr).expression);
-                    case SyntaxKind.Identifier:
-                        return nodeIsMissing(expr) ? 0 : evaluateEnumMember(expr, getSymbolOfNode(member.parent), (<Identifier>expr).escapedText);
+                    case SyntaxKind.Identifier: {
+                        const id = expr as Identifier;
+                        return nodeIsMissing(expr) ? 0 : evaluateEnumMember(id, getSymbolOfNode(member.parent), id.escapedText);
+                    }
                     case SyntaxKind.ElementAccessExpression:
                     case SyntaxKind.PropertyAccessExpression:
                         const ex = <PropertyAccessExpression | ElementAccessExpression>expr;
@@ -21876,15 +21878,15 @@ namespace ts {
                                     Debug.assert(isLiteralExpression(argument));
                                     name = escapeLeadingUnderscores((argument as LiteralExpression).text);
                                 }
-                                return evaluateEnumMember(expr, type.symbol, name);
+                                return evaluateEnumMember(ex, type.symbol, name);
                             }
                         }
                         break;
                 }
                 return undefined;
             }
 
-            function evaluateEnumMember(expr: Expression, enumSymbol: Symbol, name: __String) {
+            function evaluateEnumMember(expr: Identifier | ElementAccessExpression | PropertyAccessExpression, enumSymbol: Symbol, name: __String): string | number {
                 const memberSymbol = enumSymbol.exports.get(name);
                 if (memberSymbol) {
                     const declaration = memberSymbol.valueDeclaration;
@@ -21896,6 +21898,12 @@ namespace ts {
                         return 0;
                     }
                 }
+                else {
+                    const type = checkExpression(expr);
+                    if (type.flags & TypeFlags.StringOrNumberLiteral) {
+                        return (type as LiteralType).value;
+                    }
+                }
                 return undefined;
             }
         }

tests/baselines/reference/enumInitializers_const.js

@@ -0,0 +1,19 @@
+//// [enumInitializers_const.ts]
+const stride = 5;
+const enum E {
+    x = stride * 2,
+}
+E.x;
+
+const s = "abc";
+const enum S {
+    abc = s,
+}
+S.abc;
+
+
+//// [enumInitializers_const.js]
+var stride = 5;
+10 /* x */;
+var s = "abc";
+"abc" /* abc */;

tests/baselines/reference/enumInitializers_const.symbols

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/enumInitializers_const.ts ===
+const stride = 5;
+>stride : Symbol(stride, Decl(enumInitializers_const.ts, 0, 5))
+
+const enum E {
+>E : Symbol(E, Decl(enumInitializers_const.ts, 0, 17))
+
+    x = stride * 2,
+>x : Symbol(E.x, Decl(enumInitializers_const.ts, 1, 14))
+>stride : Symbol(stride, Decl(enumInitializers_const.ts, 0, 5))
+}
+E.x;
+>E.x : Symbol(E.x, Decl(enumInitializers_const.ts, 1, 14))
+>E : Symbol(E, Decl(enumInitializers_const.ts, 0, 17))
+>x : Symbol(E.x, Decl(enumInitializers_const.ts, 1, 14))
+
+const s = "abc";
+>s : Symbol(s, Decl(enumInitializers_const.ts, 6, 5))
+
+const enum S {
+>S : Symbol(S, Decl(enumInitializers_const.ts, 6, 16))
+
+    abc = s,
+>abc : Symbol(S.abc, Decl(enumInitializers_const.ts, 7, 14))
+>s : Symbol(s, Decl(enumInitializers_const.ts, 6, 5))
+}
+S.abc;
+>S.abc : Symbol(S.abc, Decl(enumInitializers_const.ts, 7, 14))
+>S : Symbol(S, Decl(enumInitializers_const.ts, 6, 16))
+>abc : Symbol(S.abc, Decl(enumInitializers_const.ts, 7, 14))
+

tests/baselines/reference/enumInitializers_const.types

@@ -0,0 +1,35 @@
+=== tests/cases/compiler/enumInitializers_const.ts ===
+const stride = 5;
+>stride : 5
+>5 : 5
+
+const enum E {
+>E : E
+
+    x = stride * 2,
+>x : E
+>stride * 2 : number
+>stride : 5
+>2 : 2
+}
+E.x;
+>E.x : E
+>E : typeof E
+>x : E
+
+const s = "abc";
+>s : "abc"
+>"abc" : "abc"
+
+const enum S {
+>S : S
+
+    abc = s,
+>abc : S
+>s : "abc"
+}
+S.abc;
+>S.abc : S
+>S : typeof S
+>abc : S
+

tests/baselines/reference/enumInitializers_const_circular.errors.txt

@@ -0,0 +1,11 @@
+tests/cases/compiler/enumInitializers_const_circular.ts(3,9): error TS2474: In 'const' enum declarations member initializer must be constant expression.
+
+
+==== tests/cases/compiler/enumInitializers_const_circular.ts (1 errors) ====
+    const x = E.y;
+    const enum E {
+        y = x,
+            ~
+!!! error TS2474: In 'const' enum declarations member initializer must be constant expression.
+    }
+

tests/baselines/reference/enumInitializers_const_circular.js

@@ -0,0 +1,9 @@
+//// [enumInitializers_const_circular.ts]
+const x = E.y;
+const enum E {
+    y = x,
+}
+
+
+//// [enumInitializers_const_circular.js]
+var x = E.y;

tests/baselines/reference/enumInitializers_const_circular.symbols

@@ -0,0 +1,15 @@
+=== tests/cases/compiler/enumInitializers_const_circular.ts ===
+const x = E.y;
+>x : Symbol(x, Decl(enumInitializers_const_circular.ts, 0, 5))
+>E.y : Symbol(E.y, Decl(enumInitializers_const_circular.ts, 1, 14))
+>E : Symbol(E, Decl(enumInitializers_const_circular.ts, 0, 14))
+>y : Symbol(E.y, Decl(enumInitializers_const_circular.ts, 1, 14))
+
+const enum E {
+>E : Symbol(E, Decl(enumInitializers_const_circular.ts, 0, 14))
+
+    y = x,
+>y : Symbol(E.y, Decl(enumInitializers_const_circular.ts, 1, 14))
+>x : Symbol(x, Decl(enumInitializers_const_circular.ts, 0, 5))
+}
+

tests/baselines/reference/enumInitializers_const_circular.types

@@ -0,0 +1,15 @@
+=== tests/cases/compiler/enumInitializers_const_circular.ts ===
+const x = E.y;
+>x : E
+>E.y : E
+>E : typeof E
+>y : E
+
+const enum E {
+>E : E
+
+    y = x,
+>y : E
+>x : E
+}
+

tests/cases/compiler/enumInitializers_const.ts

@@ -0,0 +1,11 @@
+const stride = 5;
+const enum E {
+    x = stride * 2,
+}
+E.x;
+
+const s = "abc";
+const enum S {
+    abc = s,
+}
+S.abc;

tests/cases/compiler/enumInitializers_const_circular.ts

@@ -0,0 +1,4 @@
+const x = E.y;
+const enum E {
+    y = x,
+}