fix(core): context value for feature flag should be parsed for boolean

packages/aws-cdk-lib/core/lib/feature-flags.ts

@@ -32,6 +32,18 @@ export class FeatureFlags {
       }
       return true;
     }
-    return context !== undefined ? Boolean(context) : cxapi.futureFlagDefault(featureFlag);
+    if (context === undefined) {
+      return cxapi.futureFlagDefault(featureFlag);
+    }
+    if (typeof context === 'string') {
+      let parsedContext;
+      try {
+        parsedContext = JSON.parse(context.trim().toLowerCase());
+      } catch (e) {
+        throw new Error(`Feature flag '${featureFlag}' expected boolean context, but instead got '${context}'`);
+      }
+      return Boolean(parsedContext);
+    }
+    return Boolean(context);
   }
 }

packages/aws-cdk-lib/core/test/feature-flags.test.ts

@@ -31,5 +31,13 @@ describe('feature flags', () => {
       const actual = FeatureFlags.of(stack).isEnabled(cxapi.NEW_STYLE_STACK_SYNTHESIS_CONTEXT);
       expect(actual).toEqual(true);
     });
+
+    test('strings are evaluated as boolean', () => {
+      const stack = new Stack();
+      stack.node.setContext(cxapi.NEW_STYLE_STACK_SYNTHESIS_CONTEXT, 'false');
+
+      const actual = FeatureFlags.of(stack).isEnabled(cxapi.NEW_STYLE_STACK_SYNTHESIS_CONTEXT);
+      expect(actual).toEqual(false);
+    });
   });
 });