feat(validation): add static feature flag usage validation at build time

README.md

@@ -13,7 +13,8 @@ Lightweight, environment-based feature flag system for Nuxt 3 — made for devel
 - 🔐 Limit access to specific APIs by feature flag in server handlers
 - 🎯 Roll out features to internal QA teams without branching or releases
 - 📆 Schedule feature launches for specific environments or timeframes
-
+  🕵️‍♀️ Detect undeclared feature flags at build time with configurable validation and precise file context
+- 
 ## Planned Features
 
 - 🧩 Nuxt DevTools integration with a Feature Flag Explorer and Environment Switcher
@@ -23,8 +24,6 @@ Lightweight, environment-based feature flag system for Nuxt 3 — made for devel
 - 🧍‍♂️ Show features only for specific users (e.g., staff-only UIs, admin panels etc.)
 - 🧬 Environment inheritance which lets environments inherit feature flags from others
 - 💡 Flag descriptions / metadata for better documentation, DevTools tooltips, or internal usage notes
-- 🕵️ Unused flag detection to warn about declared flags that are never used in your app
-- 🚨 Strict mode to throw errors or warnings if a used feature flag is not declared in the config
 - 🛠 Programmatic overrides to toggle or override feature flags dynamically at runtime (e.g., per user or session)
 
 ## Quick Setup

package.json

@@ -64,6 +64,7 @@
     "@types/node": "latest",
     "changelogen": "^0.6.1",
     "eslint": "^9.26.0",
+    "globby": "^14.1.0",
     "nuxt": "^3.17.3",
     "typescript": "~5.8.3",
     "vitest": "^3.1.3",

playground/middleware/feature-not-existing-flag.ts

@@ -0,0 +1,6 @@
+export default defineNuxtRouteMiddleware(() => {
+  const { isEnabled } = useFeatureFlag()
+  if (!isEnabled('notExistingFlagMiddleware')) {
+    return showError({ statusCode: 404, statusMessage: 'Not available' })
+  }
+})

playground/nuxt.config.ts

@@ -36,5 +36,10 @@ export default defineNuxtConfig({
       staging: ['newSystem'],
       production: [],
     },
+    validation: {
+      mode: 'warn',
+      includeGlobs: ['**/*.{vue,ts,js}'],
+      excludeGlobs: ['node_modules', '.nuxt', 'dist'],
+    },
   },
 })

playground/pages/index.vue

@@ -77,6 +77,19 @@
       </div>
     </div>
 
+    <!-- Non-existing feature flag use to trigger strict mode -->
+    <div class="hidden">
+      <p v-feature="'nonExistingFlagDirective'">
+        This paragraph is only visible if the non-existing flag is enabled. It is using the v-feature directive to conditionally render content based on the feature flag status.
+      </p>
+    </div>
+
+    <div class="hidden">
+      <p v-if="isEnabled('nonExistingFlagVif')">
+        This paragraph is only visible if the non-existing flag is enabled. It is using the v-if directive to conditionally render content based on the feature flag status.
+      </p>
+    </div>
+
     <!-- Modal -->
     <div
       v-if="showBetaModal"