[6.x] Allow Live Preview while creating entries

resources/js/components/entries/PublishForm.vue

@@ -476,7 +476,7 @@ export default {
         },
 
         showLivePreviewButton() {
-            return !this.isPreviewing && !this.readOnly && !this.isCreating && this.isBase && this.livePreviewUrl;
+            return !this.isPreviewing && !this.readOnly && this.isBase && this.livePreviewUrl;
         },
 
         showVisitUrlButton() {

src/Stache/Repositories/EntryRepository.php

@@ -188,8 +188,13 @@ public static function bindings(): array
 
     public function substitute($item)
     {
-        Blink::store('entry-uris')->forget($item->id());
-        $this->substitutionsById[$item->id()] = $item;
+        // An entry being previewed before its first save has no id yet,
+        // so it can only be found by its URI.
+        if ($id = $item->id()) {
+            Blink::store('entry-uris')->forget($id);
+            $this->substitutionsById[$id] = $item;
+        }
+
         $this->substitutionsByUri[$item->locale().'@'.$item->uri()] = $item;
     }
 

tests/Feature/Entries/SubstitutesEntryForLivePreviewTest.php

@@ -6,6 +6,7 @@
 use Facades\Tests\Factories\EntryFactory;
 use Illuminate\Support\Facades\Route;
 use PHPUnit\Framework\Attributes\Test;
+use Statamic\Facades\Collection;
 use Statamic\Facades\Entry;
 use Statamic\Facades\Token;
 use Statamic\View\View;
@@ -70,6 +71,25 @@ public function it_substitutes()
             ->assertHeader('X-Statamic-Live-Preview', true);
     }
 
+    #[Test]
+    public function it_substitutes_an_entry_that_has_not_been_saved_yet()
+    {
+        Collection::make('test')->routes('/test/{slug}')->template('entry')->save();
+        $this->viewShouldReturnRaw('layout', '{{ template_content }}');
+        $this->viewShouldReturnRaw('entry', '{{ title }} {{ foo }}');
+
+        $substitute = EntryFactory::collection('test')->slug('delta')->data(['title' => 'New title', 'foo' => 'New foo'])->make();
+        LivePreview::tokenize('test-token', $substitute);
+
+        $this->assertNull($substitute->id());
+
+        $this->get('/test/delta?token=test-token')
+            ->assertOk()
+            ->assertSee('New title')
+            ->assertSee('New foo')
+            ->assertHeader('X-Statamic-Live-Preview', true);
+    }
+
     #[Test]
     public function it_doesnt_substitute()
     {