✨ Throw when snapshot options result in no snapshots

packages/core/src/percy.js

@@ -372,14 +372,13 @@ export class Percy {
         if (!options.snapshots) options.sitemap = new URL('sitemap.xml', options.baseUrl).href;
       }
 
-      let snapshots = options.snapshots ||
+      let snapshots = mapSnapshotOptions((options.snapshots ||
         ('sitemap' in options && await getSitemapSnapshots(options)) ||
-        ('url' in options && [options]);
-
-      await Promise.all(mapSnapshotOptions(snapshots, options, (
-        snapshot => this._takeSnapshot(snapshot)
-      )));
+        ('url' in options && [options])
+      ), options);
 
+      if (!snapshots.length) throw new Error('No snapshots found');
+      await Promise.all(snapshots.map(s => this._takeSnapshot(s)));
       await server?.close();
     });
   }

packages/core/src/snapshot.js

@@ -75,16 +75,18 @@ export function snapshotMatches(snapshot, include, exclude) {
 }
 
 // Accepts an array of snapshots to filter and map with matching options.
-export function mapSnapshotOptions(snapshots, config, map) {
+export function mapSnapshotOptions(snapshots, config) {
+  if (!snapshots?.length) return [];
+
   // reduce options into a single function
   let applyOptions = [].concat(config?.options || [])
     .reduceRight((next, { include, exclude, ...opts }) => snap => next(
       // assign additional options to included snaphots
       snapshotMatches(snap, include, exclude) ? Object.assign(snap, opts) : snap
-    ), map);
+    ), s => s);
 
   // reduce snapshots with overrides
-  return [...snapshots].reduce((acc, snapshot) => {
+  return snapshots.reduce((acc, snapshot) => {
     // transform snapshot URL shorthand into an object
     if (typeof snapshot === 'string') snapshot = { url: snapshot };
 
@@ -157,7 +159,7 @@ export async function getSitemapSnapshots(options) {
     }
 
     // parse XML content into a list of URLs
-    let urls = body.match(/(?<=<loc>)(.*)(?=<\/loc>)/ig);
+    let urls = body.match(/(?<=<loc>)(.*)(?=<\/loc>)/ig) ?? [];
 
     // filter out duplicate URLs that differ by a trailing slash
     return urls.filter((url, i) => {

packages/core/test/snapshot-multiple.test.js

@@ -195,6 +195,14 @@ describe('Snapshot multiple', () => {
         'The sitemap must be an XML document, but the content-type was "text/html"'
       );
     });
+
+    it('throws when a sitemap is empty', async () => {
+      sitemap = [];
+
+      await expectAsync(percy.snapshot({
+        sitemap: 'http://localhost:8000/sitemap.xml'
+      })).toBeRejectedWithError('No snapshots found');
+    });
   });
 
   describe('server syntax', () => {