[6.x] Give each Stache traversal its own filter

src/Stache/Traverser.php

@@ -37,8 +37,10 @@ public function traverse($store)
 
     public function filter($filter)
     {
-        $this->filter = $filter;
+        $clone = clone $this;
 
-        return $this;
+        $clone->filter = $filter;
+
+        return $clone;
     }
 }

tests/Stache/TraverserTest.php

@@ -8,8 +8,11 @@
 use PHPUnit\Framework\Assert as PHPUnit;
 use PHPUnit\Framework\Attributes\Test;
 use Statamic\Facades\Path;
+use Statamic\Facades\Stache as StacheFacade;
 use Statamic\Stache\Stache;
 use Statamic\Stache\Stores\BasicStore;
+use Statamic\Stache\Stores\CollectionsStore;
+use Statamic\Stache\Stores\EntriesStore;
 use Statamic\Stache\Traverser;
 use Symfony\Component\Finder\SplFileInfo;
 use Tests\TestCase;
@@ -124,4 +127,46 @@ public function makeItemFromFile($path, $contents)
             $dir.'/three.txt' => 1234567893,
         ], $files->all());
     }
+
+    #[Test]
+    public function filtering_does_not_change_the_filter_of_the_original_instance()
+    {
+        touch($this->tempDir.'/one.txt');
+        touch($this->tempDir.'/two.yaml');
+
+        $store = Mockery::mock();
+        $store->shouldReceive('directory')->andReturn($this->tempDir);
+
+        $txt = $this->traverser->filter(fn ($file) => $file->getExtension() === 'txt');
+        $yaml = $this->traverser->filter(fn ($file) => $file->getExtension() === 'yaml');
+
+        $dir = Path::tidy($this->tempDir);
+        $this->assertSame([$dir.'/one.txt'], $txt->traverse($store)->keys()->all());
+        $this->assertSame([$dir.'/two.yaml'], $yaml->traverse($store)->keys()->all());
+        $this->assertCount(2, $this->traverser->traverse($store));
+    }
+
+    #[Test]
+    public function a_traversal_started_by_a_filter_does_not_replace_the_running_traversals_filter()
+    {
+        $this->setSites([
+            'en' => ['url' => '/', 'locale' => 'en_US'],
+            'fr' => ['url' => '/fr/', 'locale' => 'fr_FR'],
+        ]);
+
+        mkdir($this->tempDir.'/blog/en', 0777, true);
+        file_put_contents($this->tempDir.'/blog.yaml', "sites:\n  - en\n  - fr\n");
+
+        foreach (['alpha', 'bravo', 'charlie'] as $slug) {
+            file_put_contents($this->tempDir."/blog/en/{$slug}.md", "---\nid: {$slug}\ntitle: {$slug}\n---\n");
+        }
+
+        // On multisite, the entries store's filter resolves the collection, and on
+        // a cold cache that builds the collections store from disk while the
+        // entries traversal is still looping over its files.
+        StacheFacade::registerStore((new CollectionsStore)->directory($this->tempDir));
+        StacheFacade::registerStore((new EntriesStore)->directory($this->tempDir));
+
+        $this->assertCount(3, StacheFacade::store('entries')->store('blog')->paths());
+    }
 }