chore: add knip and eslint-plugin-lit

- Configure knip with strict rules (all set to error)
- Add eslint-plugin-lit for Lit-specific linting
- Add to pre-commit hook and CI pipeline
- Fix detected issues: remove unused exports and files

Author: Ondrej Machala

.github/workflows/ci.yml

@@ -38,6 +38,9 @@ jobs:
       - name: Type check
         run: pnpm typecheck
 
+      - name: Check unused code
+        run: pnpm knip
+
       - name: Test with coverage
         run: pnpm vitest run --coverage
 

eslint.config.js

@@ -2,12 +2,14 @@
 import eslint from '@eslint/js';
 import tseslint from 'typescript-eslint';
 import prettierConfig from 'eslint-config-prettier';
+import litPlugin from 'eslint-plugin-lit';
 
 export default tseslint.config(
   eslint.configs.recommended,
   ...tseslint.configs.strictTypeChecked,
   ...tseslint.configs.stylisticTypeChecked,
   prettierConfig,
+  litPlugin.configs['flat/recommended'],
   {
     languageOptions: {
       parserOptions: {

knip.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://unpkg.com/knip@5/schema.json",
+  "entry": ["src/treemap-card.ts", "src/index.ts"],
+  "project": ["src/**/*.ts"],
+  "ignore": ["src/**/*.test.ts"],
+  "ignoreDependencies": [],
+  "rules": {
+    "files": "error",
+    "dependencies": "error",
+    "devDependencies": "error",
+    "optionalPeerDependencies": "error",
+    "unlisted": "error",
+    "binaries": "error",
+    "unresolved": "error",
+    "exports": "error",
+    "nsExports": "error",
+    "classMembers": "error",
+    "types": "error",
+    "nsTypes": "error",
+    "enumMembers": "error",
+    "duplicates": "error"
+  }
+}

package.json

@@ -18,7 +18,8 @@
     "lint:fix": "eslint src/ --fix",
     "format": "prettier --write .",
     "format:check": "prettier --check .",
-    "check": "pnpm typecheck && pnpm format:check && pnpm lint && pnpm test:run",
+    "knip": "knip",
+    "check": "pnpm typecheck && pnpm format:check && pnpm lint && pnpm knip && pnpm test:run",
     "fix": "pnpm format && pnpm lint:fix",
     "prepare": "simple-git-hooks"
   },
@@ -41,7 +42,9 @@
     "custom-card-helpers": "^1.9.0",
     "eslint": "^9.16.0",
     "eslint-config-prettier": "^9.1.0",
+    "eslint-plugin-lit": "^2.1.1",
     "jsdom": "^25.0.0",
+    "knip": "^5.80.0",
     "prettier": "^3.7.4",
     "simple-git-hooks": "^2.11.1",
     "typescript": "^5.7.0",