Qualify enum member names when referencing in value position

src/compiler/checker.ts

@@ -5759,7 +5759,13 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
             // If the symbol with this name is present it should refer to the symbol
             if (symbolFromSymbolTable === symbol) {
-                // No need to qualify
+                // No need to qualify, unless this was from an enum and we're using it in a value context, e.g.
+                // enum Foo { bar }
+                // namespace Foo { export const q = Foo.bar }
+                // where we can't legally decl emit 'const q = bar'
+                if (symbol.flags & SymbolFlags.EnumMember) {
+                    qualify = true;
+                }
                 return true;
             }
 

tests/baselines/reference/invalidUnqualifiedEnum.js

@@ -0,0 +1,31 @@
+//// [tests/cases/compiler/invalidUnqualifiedEnum.ts] ////
+
+//// [invalidUnqualifiedEnum.ts]
+export enum Foo {
+    bar
+}
+export namespace Foo {
+    export const q = Foo.bar;
+}
+
+
+//// [invalidUnqualifiedEnum.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.Foo = void 0;
+var Foo;
+(function (Foo) {
+    Foo[Foo["bar"] = 0] = "bar";
+})(Foo || (exports.Foo = Foo = {}));
+(function (Foo) {
+    Foo.q = Foo.bar;
+})(Foo || (exports.Foo = Foo = {}));
+
+
+//// [invalidUnqualifiedEnum.d.ts]
+export declare enum Foo {
+    bar = 0
+}
+export declare namespace Foo {
+    const q = Foo.bar;
+}

tests/baselines/reference/invalidUnqualifiedEnum.symbols

@@ -0,0 +1,19 @@
+//// [tests/cases/compiler/invalidUnqualifiedEnum.ts] ////
+
+=== invalidUnqualifiedEnum.ts ===
+export enum Foo {
+>Foo : Symbol(Foo, Decl(invalidUnqualifiedEnum.ts, 0, 0), Decl(invalidUnqualifiedEnum.ts, 2, 1))
+
+    bar
+>bar : Symbol(Foo.bar, Decl(invalidUnqualifiedEnum.ts, 0, 17))
+}
+export namespace Foo {
+>Foo : Symbol(Foo, Decl(invalidUnqualifiedEnum.ts, 0, 0), Decl(invalidUnqualifiedEnum.ts, 2, 1))
+
+    export const q = Foo.bar;
+>q : Symbol(q, Decl(invalidUnqualifiedEnum.ts, 4, 16))
+>Foo.bar : Symbol(Foo.bar, Decl(invalidUnqualifiedEnum.ts, 0, 17))
+>Foo : Symbol(Foo, Decl(invalidUnqualifiedEnum.ts, 0, 0), Decl(invalidUnqualifiedEnum.ts, 2, 1))
+>bar : Symbol(Foo.bar, Decl(invalidUnqualifiedEnum.ts, 0, 17))
+}
+

tests/baselines/reference/invalidUnqualifiedEnum.types

@@ -0,0 +1,26 @@
+//// [tests/cases/compiler/invalidUnqualifiedEnum.ts] ////
+
+=== invalidUnqualifiedEnum.ts ===
+export enum Foo {
+>Foo : Foo
+>    : ^^^
+
+    bar
+>bar : Foo.bar
+>    : ^^^^^^^
+}
+export namespace Foo {
+>Foo : typeof Foo
+>    : ^^^^^^^^^^
+
+    export const q = Foo.bar;
+>q : Foo.bar
+>  : ^^^^^^^
+>Foo.bar : Foo
+>        : ^^^
+>Foo : typeof Foo
+>    : ^^^^^^^^^^
+>bar : Foo
+>    : ^^^
+}
+

tests/cases/compiler/invalidUnqualifiedEnum.ts

@@ -0,0 +1,8 @@
+// @declaration: true
+
+export enum Foo {
+    bar
+}
+export namespace Foo {
+    export const q = Foo.bar;
+}