fix(@angular-devkit/build-optimizer): wrap TypeScript string enums in IIFE

Fixes #14786

Author: alan-agius4

packages/angular_devkit/build_optimizer/src/transforms/wrap-enums.ts

@@ -299,11 +299,16 @@ function findTs2_3EnumIife(
     }
 
     const memberArgument = assignment.argumentExpression;
-    if (!memberArgument || !ts.isBinaryExpression(memberArgument)
-        || memberArgument.operatorToken.kind !== ts.SyntaxKind.FirstAssignment) {
-      return null;
+    // String enum
+    if (ts.isStringLiteral(memberArgument)) {
+      return [callExpression, exportExpression];
     }
 
+    // Non string enums
+    if (!ts.isBinaryExpression(memberArgument)
+      || memberArgument.operatorToken.kind !== ts.SyntaxKind.FirstAssignment) {
+      return null;
+    }
 
     if (!ts.isElementAccessExpression(memberArgument.left)) {
       return null;

packages/angular_devkit/build_optimizer/src/transforms/wrap-enums_spec.ts

@@ -514,6 +514,27 @@ describe('wrap enums and classes transformer', () => {
       expect(tags.oneLine`${transform(input)}`).toEqual(tags.oneLine`${output}`);
     });
 
+    it('wraps TS string enums in IIFE', () => {
+      const input = tags.stripIndent`
+        export var NotificationKind;
+        (function (NotificationKind) {
+            NotificationKind["NEXT"] = "N";
+            NotificationKind["ERROR"] = "E";
+            NotificationKind["COMPLETE"] = "C";
+        })(NotificationKind || (NotificationKind = {}));
+      `;
+      const output = tags.stripIndent`
+        export var NotificationKind = /*@__PURE__*/ (function (NotificationKind) {
+            NotificationKind["NEXT"] = "N";
+            NotificationKind["ERROR"] = "E";
+            NotificationKind["COMPLETE"] = "C";
+            return NotificationKind;
+        })({});
+      `;
+
+      expect(tags.oneLine`${transform(input)}`).toEqual(tags.oneLine`${output}`);
+    });
+
     it('wraps tsickle enums in IIFE', () => {
       const input = tags.stripIndent`
         /** @enum {number} */