fix: skip purgeCache in local dev (#472)

**Which problem is this pull request solving?**

Currently running `purgeCache` in local development throws an error.
While I wouldn't expect it to actually purge anything (because there's
no cache anyway), this prevents us running dev for any site that does
use this.

**Describe the solution you've chosen**

Log a message and return if called in local dev without a token. If a
token is passed I assume the user knows what they're doing and wants it
to work for real.

**Describe alternatives you've considered**

Example: Another solution would be [...]

**Checklist**

Please add a `x` inside each checkbox:

- [ ] I have read the [contribution
guidelines](../blob/master/CONTRIBUTING.md).
- [ ] The status checks are successful (continuous integration). Those
can be seen below.

---------

Co-authored-by: Marcus Weiner <marcus.weiner@gmail.com>

src/lib/purge_cache.ts

@@ -29,6 +29,7 @@ interface PurgeAPIPayload {
   site_slug?: string
 }
 
+// eslint-disable-next-line complexity
 export const purgeCache = async (options: PurgeCacheOptions = {}) => {
   if (globalThis.fetch === undefined) {
     throw new Error(
@@ -42,6 +43,12 @@ export const purgeCache = async (options: PurgeCacheOptions = {}) => {
   }
   const token = env.NETLIFY_PURGE_API_TOKEN || options.token
 
+  if (env.NETLIFY_LOCAL && !token) {
+    const scope = options.tags?.length ? ` for tags ${options.tags?.join(', ')}` : ''
+    console.log(`Skipping purgeCache${scope} in local development.`)
+    return
+  }
+
   if ('siteSlug' in options) {
     payload.site_slug = options.siteSlug
   } else if ('domain' in options) {

test/unit/purge_cache.js

@@ -13,6 +13,7 @@ const hasFetchAPI = semver.gte(process.version, '18.0.0')
 test.beforeEach(() => {
   delete process.env.NETLIFY_PURGE_API_TOKEN
   delete process.env.SITE_ID
+  delete process.env.NETLIFY_LOCAL
 })
 
 test.afterEach(() => {
@@ -90,3 +91,28 @@ test.serial('Throws if the API response does not have a successful status code',
     'Cache purge API call returned an unexpected status code: 500',
   )
 })
+
+test.serial('Ignores purgeCache if in local dev with no token or site', async (t) => {
+  if (!hasFetchAPI) {
+    console.warn('Skipping test requires the fetch API')
+
+    return t.pass()
+  }
+
+  process.env.NETLIFY_LOCAL = '1'
+
+  const mockAPI = new MockFetch().post({
+    body: () => {
+      t.fail()
+    }
+  })
+  const myFunction = async () => {
+    await purgeCache()
+  }
+
+  globalThis.fetch = mockAPI.fetcher
+
+  const response = await invokeLambda(myFunction)
+
+  t.is(response, undefined)
+})